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Ecological research on Borrelia burgdorferi sensu lato: Terminology and some methodological pitfalls
Abstract
This book contains 12 chapters. The first chapter outlines the historical and clinical aspects of Lyme borreliosis including descriptions of the disease in humans and domestic animals, and of diagnosis and treatment. The second chapter deals with ecological methods and terminology and chapters 3-5 describe the biology of the spirochaetes and their behaviour in vectors and vertebrates. The next 4 chapters (6-9) concern the ecology of Borrelia burgdorferi in Europe, Russia, South East Asia and North America, and the last 3 chapters (10-12) deal with the application of the biological and ecological attributes of the pathogens to disease epidemiology, vaccine development and ecological management of Lyme borreliosis.
... Following (Martin et al., 2016), we define reservoir competence as "the propensity of an individual host to generate new infection in other susceptible hosts." Adapted to the vector-borne system in Bbsl, this means that the bacteria have to (1) be transmitted to the reservoir host via a tick bite, (2) survive and multiply within the reservoir, and (3) subsequently be acquired in a live and infectious form by a new tick vector, enabling transmission to further hosts (Kahl et al., 2002). These three key components of reservoir competence can and should be tested experimentally as a prerequisite to field studies testing the ecological relevance of a reservoir host-Bbsl association. ...
... These three key components of reservoir competence can and should be tested experimentally as a prerequisite to field studies testing the ecological relevance of a reservoir host-Bbsl association. Just because transmission is experimentally-proven in the laboratory, it does not mean that the association occurs in nature (Eisen, 2019;Gern and Humair, 2002;Kahl et al., 2002). ...
... We identified 96 studies in the literature of 465 total consulted papers (404 after exclusion criteria were applied) that sought to experimentally establish the association of a member of Bbsl with one or several host species. This allowed us to identify seven different methods (lines of evidence) used in the literature to support key Components 1-3 of reservoir competence from (Kahl et al., 2002). In Fig. 1, we present Components 1-3 (C1-C3) as three questions that can be asked about a potential host of Bbsl (Kahl et al., 2002;Martin et al., 2016): C1) Can live bacteria be transmitted to the host by a vector tick?, C2) Can bacteria survive and multiply in the host? ...
Borrelia burgdorferi sensu lato (Bbsl) is a bacterial species complex that includes the etiological agents of the most frequently reported vector-borne disease in the Northern hemisphere, Lyme borreliosis. It currently comprises > 20 named and proposed genospecies that use vertebrate hosts and tick vectors for transmission in the Americas and Eurasia. Host (and vector) associations influence geographic distribution and speciation in Bbsl, which is of particular relevance to human health. To target gaps in knowledge for future efforts to understand broad patterns of the Bbsl-tick-host system and how they relate to human health, the present review aims to give a comprehensive summary of the literature on host association in Bbsl. Of 465 papers consulted (404 after exclusion criteria were applied), 96 sought to experimentally establish reservoir competence of 143 vertebrate host species for Bbsl. We recognize xenodiagnosis as the strongest method used, however it is infrequent (20% of studies) probably due to difficulties in maintaining tick vectors and/or wild host species in the lab. Some well-established associations were not experimentally confirmed according to our definition (ex: Borrelia garinii, Ixodes uriae and sea birds). We conclude that our current knowledge on host association in Bbsl is mostly derived from a subset of host, vector and bacterial species involved, providing an incomplete knowledge of the physiology, ecology and evolutionary history of these interactions. More studies are needed on all host, vector and bacterial species globally involved with a focus on non-rodent hosts and Asian Bbsl complex species, especially with experimental research that uses xenodiagnosis and genomics to analyze existing host associations in different ecosystems.
... annulata), which is only transmitted transstadially in vector ticks (Mehlhorn and Schein, 1984), whereas Crimean-Congo hemorrhagic fever (CCHF) virus can be transmitted via all aforementioned routes (Turell, 2007). However, at least one of these routes along with the horizontal transmission must be present in a tick for it to be considered a competent vector (Kahl et al., 2002;Pfaffle et al., 2013). In addition, if a tick species can transmit a pathogen both transovarially (with high transmission rate) and transstadially, this species is not only a vector but also a reservoir for that pathogen. ...
... Transovarial transmission-competent tick species are accepted as both competent vectors and reservoirs if their life stages can suck blood from suitable vertebrate hosts and can successfully transmit the pathogens to their next stages (Kahl et al., 2002;Parola and Raoult, 2001). Hypothetically, tick species that can transmit pathogens transovarially are important vectors for relevant pathogens. ...
... Although a tick species can transmit a certain pathogen transovarially and/or transstadially in experimental studies, the same tick may not play an important role in the transmission of that pathogen due to the life stages of the tick not naturally feeding on appropriate reservoirs or susceptible hosts. Therefore, such a tick would not be considered a natural vector of the pathogen (Kahl et al., 2002). One of the best examples is that Hy. rufipes which is not considered a natural vector of Th. annulata because their immature forms do not naturally prefer to feed on cattle. ...
This study aimed to investigate the presence of the natural transovarial transmission of tick-borne pathogens in unfed larvae obtained from engorged female ticks from domestic animals in Turkey. Larvae (n = 4530, 151 pools) obtained from 75 engorged female ticks and female carcasses were screened for the presence of certain tick-borne pathogens by PCR. The presence of transovarial transmission of Babesia occultans was detected in Hyalomma marginatum and Hy. excavatum, while Ba. ovis in Rhipicephalus bursa. Theileria annulata was detected only in Hy. excavatum and Rh. turanicus female carcasses, but not in their examined progenies. Additionally, Rickettsia aeschlimannii and Rickettsia raoultii were detected in Hy. marginatum and Dermacentor marginatus females, respectively, and all their examined larvae. Besides, Ri. slovaca was detected in a De. marginatus female carcass and its one of two examined larvae pools. The presence of mixed Ba. occultans and Ri. aeschlimannii infection was also determined in an Hy. marginatum female and its larvae. This is the first demonstration of transovarial transmission of Ba. occultans in naturally infected Hy. excavatum. These data suggested that Hy. excavatum may act as vector in the natural cycle of Ba. occultans.
... By definition, a hematophagous arthropod species that transmits a pathogen during blood-feeding is known as a vector. In this context, vector competence is the innate ability of an arthropod to acquire, maintain, and transmit microbial agents (Kahl et al., 2002;Nuttall, 2009). A competent vector of a tick-borne virus is capable of being infected from feeding on an infected host, even if viremia is transient or undetectable. ...
... The broader term "vectorial capacity" (see Table 1), comprises vector competence and any behavioral or environmental factors that may influence the spread of a pathogen by the vector, and thus denotes the relative importance that a tick species plays in the transmission of a pathogen. Vectorial capacity is a concept that considers both the ecological context of the vector (relative abundance, preferred hosts, climate tolerance) and its capacity to acquire and transmit the pathogen (Kahl et al., 2002;Rogers and Randolph, 2006;Estrada-Peña et al., 2013a). Ticks are especially well suited as pathogen vectors, first because of their hematophagous behavior (including the relatively long duration of bloodfeeding), and second because of the wide variety of vertebrates they can utilize as hosts. ...
... For tick-transmitted pathogens, a "reservoir" is commonly considered to be a vertebrate that supports the circulation of a pathogen in its blood for a period of time sufficient to allow feeding ticks to acquire the pathogen (Kahl et al., 2002). However, if the infected vertebrate becomes immune to the pathogen and is no longer a source of infection, this reservoir status may be short-lived. ...
This manuscript is part of a series of reviews that aim to cover published research on Crimean-Congo hemorrhagic fever (CCHF) and its etiological agent, CCHF virus (CCHFV). The virus is maintained and transmitted in a vertical and horizontal transmission cycle involving a variety of wild and domestic vertebrate species that act as amplification hosts, without showing signs of illness. These vertebrates have traditionally been considered reservoirs of CCHFV, but in fact they develop only a transient viremia, while the virus can persist in ticks for their entire lifespan, and can also be transmitted vertically to the next generation. As a result, ticks are now considered to be both the vector and the reservoir for the virus. CCHFV has been detected in a wide range of tick species, but only a few have been proven to be vectors and reservoirs, mainly because most published studies have been performed under a broad variety of conditions, precluding definitive characterization. This article reviews the published literature, summarizes current knowledge of the role of ticks in CCHFV maintenance and transmission and provides guidance for how to fill the knowledge gaps. Special focus is given to existing data on tick species in which vertical passage has been demonstrated under natural or experimental conditions. At the same time, we identify earlier reports that used unreliable methods and perceptions to ascribe a vector role to some species of ticks, and have contributed to confusion regarding viral transmission. We also examine epidemiological pathways of CCHFV circulation and discuss priority areas for future research.
... A reservoir host is defined by its capacity to infect ticks feeding on it (Kahl et al., 2002). One method that helps to identify reservoirs in nature is the comparison of infection rate of questing larvae and nymphs with larvae fed on the suspected host in the same habitat. ...
... Mean density (no. collected ticks/examined birds (Kahl et al., 2002)) was 2.45 ticks per bird (81/33) and infestation intensity (no. collected ticks/infested birds (Kahl et al., 2002)) reached 5.06 ticks (81/16) (Table 1). ...
... collected ticks/examined birds (Kahl et al., 2002)) was 2.45 ticks per bird (81/33) and infestation intensity (no. collected ticks/infested birds (Kahl et al., 2002)) reached 5.06 ticks (81/16) (Table 1). Maximum number of ticks collected on a single individual was 17. ...
From 2007 to 2010, 4558 migrating and breeding birds of 71 species were caught and examined for ticks in Switzerland. A total of 1205 specimens were collected; all were Ixodes ricinus ticks except one Ixodes frontalis female, which was found on a common chaffinch (Fringilla coelebs) for the first time in Switzerland. Each tick was analysed individually for the presence of Borrelia spp., Rickettsia spp., Anaplasma phagocytophilum and tick-borne encephalitis virus (TBEV). Altogether, 11.4% of birds (22 species) were infested by ticks and 39.8% of them (15 species) were carrying infected ticks. Bird species belonging to the genus Turdus were the most frequently infested with ticks and they were also carrying the most frequently infected ticks. Each tick-borne pathogen for which we tested was identified within the sample of bird-feeding ticks: Borrelia spp. (19.5%) and Rickettsia helvetica (10.5%) were predominantly detected whereas A. phagocytophilum (2%), Rickettsia monacensis (0.4%) and TBEV (0.2%) were only sporadically detected. Among Borrelia infections, B. garinii and B. valaisiana were largely predominant followed by B. afzelii, B. bavariensis, B. miyamotoi and B. burgdorferi ss. Interestingly, Candidatus Neoehrlichia mikurensis was identified in a few ticks (3.3%), mainly from chaffinches.
Our study emphasizes the role of birds in the natural cycle of tick-borne pathogens that are of human medical and veterinary relevance in Europe. According to infection detected in larvae feeding on birds we implicate the common blackbird (Turdus merula) and the tree pipit (Anthus trivialis) as reservoir hosts for Borrelia spp., Rickettsia spp. and A. phagocytophilum.
... At each blood meal, ticks thus can become integrated into the epidemiological chain of pathogen transmission, by means of the so-called transstadial (stage-to-stage, also called horizontal) or transovarial (female-to-egg, also called vertical) passages. For a tick-transmitted pathogen to persist in the environment, it must be acquired from an infected host, passed into the next active stage of the tick, and then successfully transmitted into a new host ( Kahl et al., 2002). This complicates the dynamics of a pathogen in the field, which depend upon both the survival and activity rates of the tick and the composition of the community of hosts (Estrada-Peña et al., 2013b). ...
... These laboratory tests would confirm the hypotheses built upon field studies. To qualify as a true vector of a pathogen, the tick must (i) feed on infectious vertebrates (ii) acquire the pathogen during the blood meal (iii) maintain the pathogen through one or more trans-stadial molts and (iv) transmit the pathogen to previously unexposed hosts while feeding again ( Kahl et al., 2002). Assigning vector status to a tick, based solely on the detection of nucleic acids, or reservoir status to a host species, based solely on serologic studies, is not acceptable. ...
... The interactions between the elements of any tick-hostpathogen system are thus key features to understand pathogen prevalence in questing ticks. The evaluation of such interactions is a necessary preliminary step in risk assessment, and it is therefore necessary to summarize the framework of relevant terminology proposed by Kahl et al. (2002) that was constructed to address major pitfalls in the research of the relationships among ticks, hosts and pathogens. We have included such a framework in Fig. 2. ...
... The interactions between the elements of any tick–host– pathogen system are thus key features to understand pathogen prevalence in questing ticks. The evaluation of such interactions is a necessary preliminary step in risk assessment, and it is therefore necessary to summarize the framework of relevant terminology proposed by Kahl et al. (2002) that was constructed to address major pitfalls in the research of the relationships among ticks, hosts and pathogens. We have included such a framework inFig. ...
... The detection of a pathogen in a tick is therefore insufficient to determine if it is a carrier or a vector. The chart has been developed from concepts by Kahl et al. (2002), and is partially modified from Estrada-Peña et al. (2013a). ...
... At each blood meal, ticks thus can become integrated into the epidemiological chain of pathogen transmission, by means of the so-called transstadial (stage-to-stage, also called horizontal) or transovarial (female-to-egg, also called vertical) passages. For a tick-transmitted pathogen to persist in the environment, it must be acquired from an infected host, passed into the next active stage of the tick, and then successfully transmitted into a new host ( Kahl et al., 2002). This complicates the dynamics of a pathogen in the field, which depend upon both the survival and activity rates of the tick and the composition of the community of hosts ( Estrada-Peña et al., 2013b). ...
A number of tick-borne diseases of humans have increased in incidence and geographic range over the past few decades, and there is concern that they will pose an even greater threat to public health in future. Although global warming is often cited as the underlying mechanism favoring the spread of tick-borne diseases, climate is just one of many factors that determine which tick species are found in a given geographic region, their population density, the likelihood that they will be infected with microbes pathogenic for humans and the frequency of tick–human contact. This article provides basic information needed for microbiologists to understand the many factors that affect the geographic range and population density of ticks and the risk of human exposure to infected ticks. It first briefly summarizes the life cycle and basic ecology of ticks and how ticks and vertebrate hosts interact, then reviews current understanding of the role of climate, sociodemographic factors, agricultural development and changes in human behavior that affect the incidence of tick-borne diseases. These concepts are then illustrated in specific discussions of tick-borne encephalitis and Crimean-Congo hemorrhagic fever.
... The interactions between the elements of any tick-hostpathogen system are thus key features to understand pathogen prevalence in questing ticks. The evaluation of such interactions is a necessary preliminary step in risk assessment, and it is therefore necessary to summarize the framework of relevant terminology proposed by Kahl et al. (2002) that was constructed to address major pitfalls in the research of the relationships among ticks, hosts and pathogens. We have included such a framework in Fig. 2. ...
... Reservoir capacity is dependent upon the infectivity of the host for feeding ticks and the duration of the infective period ( Mather et al., 1989;Mannelli et al., 2003;Randolph and Craine, 1995;Kahl et al., 2002), which is highly variable for the different ticktransmitted pathogens, from a few days to months. By feeding on reservoir hosts, ticks are exposed to pathogens (Fig. 2D) and they may become either non-carrier or carrier ticks. ...
... The detection of a pathogen in a tick is therefore insufficient to determine if it is a carrier or a vector. The chart has been developed from concepts by Kahl et al. (2002), and is partially modified from Estrada-Peña et al. (2013a). ...
A number of tick-borne diseases of humans have increased in incidence and geographic range over the past few decades, and there is concern that they will pose an even greater threat to public health in future. Although global warming is often cited as the underlying mechanism favoring the spread of tick-borne diseases, climate is just one of many factors that determine which tick species are found in a given geographic region, their population density, the likelihood that they will be infected with microbes pathogenic for humans and the frequency of tick-human contact. This article provides basic information needed for microbiologists to understand the many factors that affect the geographic range and population density of ticks and the risk of human exposure to infected ticks. It first briefly summarizes the life cycle and basic ecology of ticks and how ticks and vertebrate hosts interact, then reviews current understanding of the role of climate, sociodemographic factors, agricultural development and changes in human behavior that affect the incidence of tick-borne diseases. These concepts are then illustrated in specific discussions of tick-borne encephalitis and Crimean-Congo hemorrhagic fever.
... The other papers were excluded based on our exclusion criteria (Appendix S1). We calculated the mean tick burden per vertebrate species, the mean infection prevalence of A. phagocytophilum in the vertebrate species, and the mean infection prevalence of A. phagocytophilum in feeding ticks, as defined by Kahl et al. (2002) (see Appendix S1 for these calculations). ...
... We used an approach similar to Hofmeester et al. (2016) to quantify the relative importance of a vertebrate host species for producing engorged I. ricinus infected with A. phagocytophilum. This relative importance is defined as the proportional contribution of a particular host species to the total number of engorged I. ricinus infected with A. phagocytophilum in a certain area in relation to that of other host species (extension of the definition for relative reservoir capacity by Kahl et al., 2002). The relative importance of a host species (among all n species) for producing engorged I. ricinus ticks infected with the different ecotypes of A. phagocytophilum was calculated using Formula 1 (adjusted from Hofmeester et al., 2016). ...
Anaplasma phagocytophilum is a tick‐borne pathogen that has been detected in many tick and vertebrate species. It is among the most widespread tick‐borne pathogens in animals in Europe. The bacterium can be genetically divided into four ecotypes, which are linked to distinct but overlapping host species. However, knowledge about the transmission dynamics of the enzootic cycles of the different ecotypes is limited. Here, we quantified the link between the ecotypes of A. phagocytophilum, the different life stages of the tick Ixodes ricinus, and vertebrate host groups through a meta‐analysis. We extracted data on the mean I. ricinus burden and the A. phagocytophilum infection prevalence in both hosts and feeding I. ricinus from 197 papers on 77 wildlife species. With this information, we modeled the relative importance of different host taxonomic groups for the circulation of the different ecotypes of A. phagocytophilum in a theoretical assemblage of hosts with varying presence of red deer (Cervus elaphus) and densities of small mammals. We showed that the composition of the vertebrate community affects the relative abundance of different ecotypes of A. phagocytophilum in the different life stages of I. ricinus. The presence of red deer is likely to increase the infection prevalence of Ecotype 1 in ticks, while small mammal densities drive the prevalence in ticks of mainly Ecotype 3, and to a lesser extent Ecotype 1. In Europe, vertebrate communities are changing, with an increase in red deer abundance and changes in the population dynamics of small mammals. Our results suggest that these changes could imply an increase in the circulation of A. phagocytophilum and thus an increase in the risk for public and veterinary health.
... For ticks to transmit diseases, they must be acquired from an infected host, passed into the next active stage, then successfully transmitted into a new host (Kahl et al., 2002;. At each blood meal, ticks can become integrated into the epidemiological chain of pathogen transmission by transstadial (stage to stage or horizontal transmission) or transovarial (female to egg, or vertical transmission) passage (Kahl et al., 2002;Estrada-Peña & De la Fuente, 2014). ...
... For ticks to transmit diseases, they must be acquired from an infected host, passed into the next active stage, then successfully transmitted into a new host (Kahl et al., 2002;. At each blood meal, ticks can become integrated into the epidemiological chain of pathogen transmission by transstadial (stage to stage or horizontal transmission) or transovarial (female to egg, or vertical transmission) passage (Kahl et al., 2002;Estrada-Peña & De la Fuente, 2014). Walker et al. (2003) define transovarial transmission as that which occurs when a microorganism is transmitted from one vertebrate host to another by infecting a female vector, then passing it through the eggs to the larvae. ...
Ticks are the most important external parasites of cattle and are known to transmit more pathogens than any other group of arthropods worldwide. About 80% of the world cattle population is at risk of ticks and tick-borne diseases, causing a global annual loss of $US22-30 billion. In Africa, the impact of ticks is ranked high, and they transmit diseases such as cowdriosis, anaplasmosis, bovine babesiosis and theileriosis. A range expansion of ixodid ticks has been observed in Africa, in particular for the genera Amblyomma and Rhipicephalus, which contribute greatly to cattle loss owing to morbidity and mortality. Distributional changes in ticks can lead to the emergence or re-emergence of infectious and parasitic diseases. Climate change is frequently invoked as the primary cause of tick distribution, but it is not the only factor. Human lifestyle changes, including transportation of livestock within countries, have promoted the introduction of new tick species and the diseases they transmit. One such example is the spread of the Asian cattle tick Rhipicephalus (Boophilus) microplus to West Africa. Rhipicephalus (Boophilus) microplus was recorded for the first time in Namibia and was probably introduced into Namibia from South Africa. Likewise, Amblyomma variegatum, the vector of heartwater disease, has the largest distribution in Africa. Its spread is outside its native range and it is considered the second most invasive tick species after R. (B.) microplus on the continent. Rhipicephalus (Boophilus) microplus is a one-host tick that is reported to be resistant to conventional acaricides and this contributes largely to its spread into non-endemic areas.
... Un grand nombre d'espèces de tiques parasitent les reptiles et plus spécialement les lézards (Bernard & Durden, 2000). Ces derniers, lorsqu'ils sont parasités par des tiques (Ixodes), sont considérés comme réservoirs compétents de Borrelia (Matuschka et al., 1999, Keirans et al., 1996, Hayashi & Hasegawa, 1984, Lane & Loye, 1989, Kahl et al., 2002, Manweiler et al., 1991, Eisen & Eisen, 2001) et dans quelques exceptions comme réservoir incompétents (Dsouli et al. ...
... ). Il peut s'agir d'oiseaux(Matuschka et al., 1991) de mammifères(Matuschka et al., 1991, Eisen et al., 2004 ou de reptiles(Keirans et al., 1996, Olsen et al., 1993, Kahl et al., 2002. Ces agents pathogènes sont inoculés par des ectoparasites hématophages et peuvent être soit des insectes soit des acariens. ...
Feeding ecology of the common genet
(Genetta genetta) in a forest
ecosystem of El Kala National Park
(North-East Algeria).
The study of the diet of the common genet
(Genetta genetta L. 1758) was performed
conducted in a forest ecosystem of El Kala
National Park (North-East Algeria). Using the
coprologic method we identified at least 723 preys
belonging to 5 food categories (mammals, birds,
arthropods, reptiles / amphibians and plants). The
statistical analysis allowed us to identify an equal
balance of arthropods and mammals, followed by
the plants, birds, and the class of Reptiles /
amphibians. The seasonal analysis of different
stand structure prey-item parameters gives to
common genet a "generalist" status with broad
spectrum food.
... North Kahl et al., 2002; Mannelli et al., 2011; Stanek and Reiter, 2011; Margos et al., 2014). Populations of these Borrelia spirochetes are maintained in the wild by a variety of vertebrate hosts and are spread from host to host mainly by ticks of the genus Ixodes. ...
... A wide range of vertebrates host I. pacificus ticks, but these host species vary in their reservoir competence. As defined by Kahl et al. (2002), a vertebrate reservoir host must be able to: (i) host vector ticks, (ii) acquire B. burgdorferi from infected ticks, (iii) allow the bacteria to multiply and persist in its body, and (iv) transmit spirochetes back to feeding vector ticks. Non-reservoir hosts are ecological barriers to Borrelia spirochetes. ...
The Western Fence Lizard (Sceloporus occidentalis) is a major host of juvenile stages of the Western Black-legged Tick (Ixodes pacificus), which is the vector for the Lyme disease causative spirochete bacterium Borrelia burgdorferi in the western United States. Because S. occidentalis is reservoir incompetent and capable of eliminating spirochetes from infected ticks, it has been implicated as a major factor in the ecology of Lyme disease in the West. Although complement proteins in lizard blood have been established as the borreliacidal factor, no studies have examined intraspecific variability in host lizard borreliacidal capacity. In Chapter 1 of this thesis, we introduce the complexity of the Borrelia burgdorferi transmission cycle and it’s implications for transmission risk. In Chapter 2 we tested the hypothesis that host lizard physiological condition impacts their borreliacidal capacity. Blood plasma of lizards in varying physiological conditions was challenged against cultured B. burgdorferi, and the complement-mediated inactivation of spirochetes was quantified. Adult lizards had higher bactericidal activity than first-year juveniles, suggesting that complement-mediated inactivation develops with maturity and/or exposure to spirochete antigens. Also, bactericidal activity was positively associated with lizard tick load and body condition. Adult lizard sex did not significantly affect spirochete mortality. Lizards from an inland site with little exposure to ticks had higher bactericidal activity than lizards from a coastal population that is heavily parasitized by ticks.
... Un grand nombre d'espèces de tiques parasitent les reptiles et plus spécialement les lézards (Bernard & Durden, 2000). Ces derniers, lorsqu'ils sont parasités par des tiques (Ixodes), sont considérés comme réservoirs compétents de Borrelia (Matuschka et al., 1999, Keirans et al., 1996, Hayashi & Hasegawa, 1984, Lane & Loye, 1989, Kahl et al., 2002, Manweiler et al., 1991, Eisen & Eisen, 2001) et dans quelques exceptions comme réservoir incompétents (Dsouli et al. ...
... ). Il peut s'agir d'oiseaux(Matuschka et al., 1991) de mammifères(Matuschka et al., 1991, Eisen et al., 2004 ou de reptiles(Keirans et al., 1996, Olsen et al., 1993, Kahl et al., 2002. Ces agents pathogènes sont inoculés par des ectoparasites hématophages et peuvent être soit des insectes soit des acariens. ...
The site of Bou Nemrou, in the Western
Tafilalt (eastern Anti-Atlas, Morocco) is one
of the very few Konservat-Lagerstätten
known so far in the world to have yielded
numerous remains of Late Ordovician softbodied
fossils associated with an abundant
and diverse marine benthic fauna. This
locality has also yielded several levels
(starfish beds) extremely rich in exquisitely
preserved echinoderms. Their remarkable
preservation possibly results from the rapid,
in situ burial of large, particularly dense,
living communities (echinoderm meadows)
by storm deposits. The Bou Nemrou starfish
beds are dominated by eocrinoids and
stylophorans, associated with crinoids,
cyclocystoids, edrioasteroids, and
ophiuroids. This composition is typical of the
cool assemblages of the Mediterranean
Province. The Bou Nemrou starfish beds
may result from the opportunistic
colonisation of the sea-floor by dense
populations of echinoderms, during short
phases of environmental disturbance.
... It is possible that the humans had bacteremia of B. burgdorferi sensu stricto and this pathogen passed to the ticks during the feeding process or the ticks might have been infected in previous life stages, as well. As noted by Kahl et al. (2002): ''to be considered a vector, a tick species must: (1) feed on infectious vertebrates; (2) be able to acquire the pathogen during the blood meal; (3) maintain it through one ore more life stages (transstadial passage); and (4) pass it on to other host when feeding again. Otherwise it is a non-vector tick'' [45]. ...
... As noted by Kahl et al. (2002): ''to be considered a vector, a tick species must: (1) feed on infectious vertebrates; (2) be able to acquire the pathogen during the blood meal; (3) maintain it through one ore more life stages (transstadial passage); and (4) pass it on to other host when feeding again. Otherwise it is a non-vector tick'' [45]. Therefore, more detailed experimental studies are required to determine the vector competence of these tick species. ...
Background:
The importance of tick-borne diseases is increasing all over the world, including Turkey. The tick-borne disease outbreaks reported in recent years and the abundance of tick species and the existence of suitable habitats increase the importance of studies related to the epidemiology of ticks and tick-borne pathogens in Turkey. The aim of this study was to investigate the presence of and to determine the infection rates of some tick-borne pathogens, including Babesia spp., Borrelia burgdorferi sensu lato and spotted fever group rickettsiae in the ticks removed from humans in different parts of Ankara.
Methodology/principal findings:
A total of 169 ticks belonging to the genus Haemaphysalis, Hyalomma, Ixodes and Rhipicephalus were collected by removing from humans in different parts of Ankara. Ticks were molecularly screened for Babesia spp., Borrelia burgdorferi sensu lato and spotted fever group rickettsiae by PCR and sequencing analysis. We detected 4 Babesia spp.; B. crassa, B. major, B. occultans and B. rossi, one Borrelia spp.; B. burgdorferi sensu stricto and 3 spotted fever group rickettsiae; R. aeschlimannii, R. slovaca and R. hoogstraalii in the tick specimens analyzed. This is the report showing the presence of B. rossi in a region that is out of Africa and in the host species Ha. parva. In addition, B. crassa, for which limited information is available on its distribution and vector species, and B. occultans, for which no conclusive information is available on its presence in Turkey, were identified in Ha. parva and H. marginatum, respectively. Two human pathogenic rickettsia species (R. aeschlimannii and R. slovaca) were detected with a high prevalence in ticks. Additionally, B. burgdorferi sensu stricto was detected in unusual tick species (H. marginatum, H. excavatum, Hyalomma spp. (nymph) and Ha. parva).
Conclusions/significance:
This study investigates both the distribution of several tick-borne pathogens affecting humans and animals, and the presence of new tick-borne pathogens in Turkey. More epidemiological studies are warranted for B. rossi, which is very pathogenic for dogs, because the presented results suggest that B. rossi might have a wide distribution in Turkey. Furthermore, we recommend that tick-borne pathogens, especially R. aeschlimannii, R. slovaca, and B. burgdorferi sensu stricto, should be taken into consideration in patients who had a tick bite in Turkey.
... It must be pointed out that the finding of any tick-borne pathogens in ticks removed from hosts (2011) is no proof of vector competence. Without proven capability of transmission the vector function of a given tick species for a given pathogen is not substantiated (Kahl et al. 2002). Transmission studies with I. trianguliceps are only available for Babesia microti, which were carried out for the first time by Young (1970) in the United Kingdom. ...
The Eurasian shrew and vole tick Ixodes trianguliceps Birula lives in the nests and burrows of its small mammalian hosts and is-along with larvae and nymphs of Ixodes ricinus or Ixodes persulcatus-one of the most commonly collected tick species from these hosts in its Eurasian range. Ixodes trianguliceps is a proven vector of Babesia microti. In this study, up-to-date maps depicting the geographical distribution and the climate preference of I. trianguliceps are presented. A dataset was compiled, resulting in 1161 georeferenced locations in Eurasia. This data set covers the entire range of I. trianguliceps for the first time. The distribution area between 8[Formula: see text] W-105[Formula: see text] E and 40-69[Formula: see text] N extends from Northern Spain to Western Siberia. To investigate the climate adaptation of I. trianguliceps, the georeferenced locations were superimposed on a high-resolution map of the Köppen-Geiger climate classification. The Köppen profile for I. trianguliceps, i.e., a frequency distribution of the tick occurrence under different climates, shows two peaks related to the following climates: warm temperate with precipitation all year round (Cfb), and boreal with warm or cold summers and precipitation all year round (Dfb, Dfc). Almost 97% of all known I. trianguliceps locations are related to these climates. Thus, I. trianguliceps prefers climates with warm or cold summers without dry periods. Cold winters do not limit the distribution of this nidicolous tick species, which has been recorded in the European Alps and the Caucasus Mountains up to altitudes of 2400 m. Conversely, I. trianguliceps does not occur in the Mediterranean area with its hot and dry summers.
... Lastly, venereal or sexual transmission occurs during the mating of ticks. For a tick to be considered a competent vector, horizontal transmission and at least one of these other transmission routes must be present (Kahl et al. 2002;Pfaffle et al. 2013;Schnittger et al. 2022). ...
Transovarial transmission (TOT) is an efficient vertical transmission of pathogens that is observed in many arthropod vectors. This method seems to be an evolutionarily unique development observed only in Babesia sensu stricto (clade VI) and Rickettsia spp., whereas transstadial transmission is the common/default way of transmission. Transovarial transmission does not necessarily contribute to the amplification of tick-borne pathogens but does contribute to the maintenance of disease in the environment. This review aims to provide an updated summary of previous reports on TOT of tick-borne pathogens.
... It is important to note that this study does not intend to attain vectorial status of any tick species in which the presence of a TBP was found, because the detection of a pathogen in feeding/engorged ticks does not definitively indicate that the pathogen originated from tick infection or its blood-meal (Kahl et al., 2002). Therefore, the current study has mainly focused on the characterization of TBPs circulating within the pathogen-vector-host triangle, and intended to provide novel epidemiological data and to contribute towards the related literature. ...
Grazing domestic ruminants serve as important reservoirs and/or amplificatory hosts in the ecology of tick-borne pathogens (TBPs) and tick vectors in the natural foci; however, many enzootic life cycles including ruminants and ticks are still unknown. This study investigated a wide range of TBPs circulating among ticks and grazing ruminants in the natural foci of Anatolia, Turkey. Tick specimens (n = 1815) were collected from cattle, sheep, and goats in three ecologically distinct areas (wooded, transitional, and semi-arid zones) of Anatolia and identified by species: Dermacentor marginatus, Dermacentor reticulatus, Hyalomma anatolicum, Hyalomma excavatum, Hyalomma marginatum, Hyalomma scupense, Haemaphysalis inermis, Haemaphysalis parva, Haemaphysalis punctata, Haemaphysalis sulcata, Ixodes ricinus, Rhipicephalus bursa, and Rhipicephalus turanicus. PCR-sequencing analyses revealed TBPs of great diversity, with 32 different agents identified in the ticks: six Babesia spp. (Babesia occultans, Babesia crassa, Babesia microti, Babesia rossi, Babesia sp. tavsan1, and Babesia sp. Ucbas); four Theileria spp., including one putative novel species (Theileria annulata, Theileria orientalis, Theileria ovis, and Theileria sp.); one Hepatozoon sp.; four Anaplasma spp., including one novel genotype (Anaplasma phagocytophilum, Anaplasma marginale, Anaplasma ovis, and Anaplasma sp.); six unnamed Ehrlichia spp. genotypes; Neoehrlichia mikurensis; nine spotted fever group rickettsiae, including one putative novel species (Rickettsia aeschlimannii, Rickettsia slovaca, Rickettsia hoogstraalii, Rickettsia monacensis with strain IRS3, Rickettsia mongolitimonae, Rickettsia raoultii, Candidatus Rickettsia goldwasserii, Candidatus Rickettsia barbariae, and Rickettsia sp.); and Borrelia valaisiana. Detailed phylogenetic analyses showed that some of the detected pathogens represent more than one haplotype, potentially relating to the tick species or the host. Additionally, the presence of Neoehrlichia mikurensis, an emerging pathogen for humans, was reported for the first time in Turkey, expanding its geographical distribution. Consequently, this study describes some previously unknown tick-borne protozoan and bacterial species/genotypes and provides informative epidemiological data on TBPs, which are related to animal and human health, serving the one health concept.
... Although I. ricinus feeds on a broad range of vertebrate species, including rodents, birds, insectivores, reptiles, and deer, only a few species are known to act as a reservoir host for B. burgdorferi s.l., i.e., host species that participate significantly in the natural circulation of the bacteria (Gern et al. 1994(Gern et al. , 1997(Gern et al. , 1998Kahl et al. 2002;Estrada-Peña et al. 2017;Wolcott et al. 2021 (Gern et al. 1998;Kurtenbach et al. 1998Kurtenbach et al. , 2002bDsouli et al. 2006;Lindgren and Jaenson 2006;Ekner et al. 2011;Norte et al. 2013;Heylen et al. 2014aHeylen et al. , b, 2017Norte et al. 2020a). During attachment and feeding of a vector tick on a (reservoir) host, spirochetes can be transmitted from an infected tick to a host or vice versa known as systemic transmission which is the main route how ticks acquire borreliae from an infected host ( Figure 3, Kurtenbach et al. 2002b;Mannelli et al. 2011). ...
Beside mosquitoes, ticks are well-known vectors of different human pathogens. In the Northern Hemisphere, Lyme borreliosis (Eurasia, LB) or Lyme disease (North America, LD) is the most commonly occurring vector-borne infectious disease caused by bacteria of the genus Borrelia which are transmitted by hard ticks of the genus Ixodes . The reported incidence of LB in Europe is about 22.6 cases per 100,000 inhabitants annually with a broad range depending on the geographical area analyzed. However, the epidemiological data are largely incomplete, because LB is not notifiable in all European countries. Furthermore, not only differ reporting procedures between countries, there is also variation in case definitions and diagnostic procedures. Lyme borreliosis is caused by several species of the Borrelia (B.) burgdorferi sensu lato (s.l.) complex which are maintained in complex networks including ixodid ticks and different reservoir hosts. Vector and host influence each other and are affected by multiple factors including climate that have a major impact on their habitats and ecology. To classify factors that influence the risk of transmission of B. burgdorferi s.l. to their different vertebrate hosts as well as to humans, we briefly summarize the current knowledge about the pathogens including their astonishing ability to overcome various host immune responses, regarding the main vector in Europe Ixodes ricinus , and the disease caused by borreliae. The research shows, that a higher standardization of case definition, diagnostic procedures, and standardized, long-term surveillance systems across Europe is necessary to improve clinical and epidemiological data.
... We calculated the tick burden of female ticks using: where T F i is the female tick burden on host species i , P F i is the infestation prevalence of females in host species iand I F i is the infestation intensity of females in host species i . Following Kahl et al. [31] we defined the mean infestation prevalence as the proportion of hosts with feeding ticks on the body parts described above, and the mean infestation intensity as the number of ticks feeding on those body parts, for those hosts that had feeding ticks. ...
Background
Several ungulate species are feeding and propagation hosts for the tick Ixodes ricinus as well as hosts to a wide range of zoonotic pathogens. Here, we focus on Anaplasma phagocytophilum and Borrelia burgdorferi ( s.l. ), two important pathogens for which ungulates are amplifying and dilution hosts, respectively. Ungulate management is one of the main tools to mitigate human health risks associated with these tick-borne pathogens. Across Europe, different species of ungulates are expanding their ranges and increasing in numbers. It is currently unclear if and how the relative contribution to the life-cycle of I. ricinus and the transmission cycles of tick-borne pathogens differ among these species. In this study, we aimed to identify these relative contributions for five European ungulate species.
Methods
We quantified the tick load and collected ticks and spleen samples from hunted fallow deer ( Dama dama , n = 131), moose ( Alces alces , n = 15), red deer ( Cervus elaphus , n = 61), roe deer ( Capreolus capreolus , n = 30) and wild boar ( Sus scrofa , n = 87) in south-central Sweden. We investigated the presence of tick-borne pathogens in ticks and spleen samples using real-time PCR. We determined if ungulate species differed in tick load (prevalence and intensity) and in infection prevalence in their tissue as well as in the ticks feeding on them.
Results
Wild boar hosted fewer adult female ticks than any of the deer species, indicating that deer are more important as propagation hosts. Among the deer species, moose had the lowest number of female ticks, while there was no difference among the other deer species. Given the low number of infected nymphs, the relative contribution of all ungulate species to the transmission of B. burgdorferi ( s.l. ) was low. Fallow deer, red deer and roe deer contributed more to the transmission of A. phagocytophilum than wild boar.
Conclusions
The ungulate species clearly differed in their role as a propagation host and in the transmission of B. burgdorferi and A. phagocytophilum . This study provides crucial information for ungulate management as a tool to mitigate zoonotic disease risk and argues for adapting management approaches to the local ungulate species composition and the pathogen(s) of concern.
Graphic abstract
... However, the finding of any tick-borne pathogens in questing ticks is no proof of vector competence but at least confirms the state of a carrier. Without proven capability of transmission the vector function of a given tick species for a given pathogen is not substantiated (Kahl et al. 2002). Mere determination of the carrier status of fieldcollected questing ticks is only a very first step to indicate vector competence. ...
The two ixodid tick species Dermacentor reticulatus (Fabricius) and Dermacentor silvarum Olenev occur at the northern distribution limit of the genus Dermacentor in Eurasia, within the belt of \(34{-}60^\circ ~ \hbox {N}\) latitude. Whilst the distribution area of D. reticulatus extends from the Atlantic coast of Portugal to Western Siberia, that of D. silvarum extends from Western Siberia to the Pacific coast. In Western Siberia, the distribution areas of the two Dermacentor species overlap. Although the two tick species are important vectors of disease, detailed information concerning the entire distribution area, climate adaptation, and proven vector competence is still missing. A dataset was compiled, resulting in 2188 georeferenced D. reticulatus and 522 D. silvarum locations. Up-to-date maps depicting the geographical distribution and climate adaptation of the two Dermacentor species are presented. To investigate the climate adaptation of the two tick species, the georeferenced locations were superimposed on a high-resolution map of the Köppen–Geiger climate classification. The frequency distribution of D. reticulatus under different climates shows two major peaks related to the following climates: warm temperate with precipitation all year round (57%) and boreal with precipitation all year round (40%). The frequency distribution of D. silvarum shows also two major peaks related to boreal climates with precipitation all year round (30%) and boreal winter dry climates (60%). Dermacentor silvarum seems to be rather flexible concerning summer temperatures, which can range from cool to hot. In climates with cool summers D. reticulatus does not occur, it prefers warm and to a lesser extent hot summers. Lists are given in this paper for cases of proven vector competence for various agents of both Dermacentor species. For the first time, the entire distribution areas of D. reticulatus and D. silvarum were mapped using georeferenced data. Their climate adaptations were quantified by Köppen profiles.
... The immatures of some tick species can also become infected while co-feeding, via non-viremic transmission (Randolph et al., 1996). To classify a tick species as a vector of a pathogen, that tick must be able to provide at least one of the above-mentioned transmission routes (along with some other essential ecological factors, such as host preferences etc.), otherwise it is not a vector (Kahl et al., 2002). Therefore, investigating the presence of TBPs in host-seeking ticks, rather than semi-fed ticks obtained from hosts, has the potential to provide more profitable and effective ecological information. ...
This Turkey-based study investigated the presence of various tick-borne microorganisms in a broad-range of host-seeking ticks (n = 1019) that exhibit both hunter and ambusher characteristics. All collected ticks were analyzed individually via PCR-sequencing, resulting in the identification of 18 different microorganisms: six Babesia spp., including one putative novel species (Ba. occultans, Ba. crassa, Ba. rossi, Babesia sp. tavsan1, Babesia sp. tavsan2, and Babesia sp. nov.); six SFG rickettsiae (Ri. aeschlimannii, Ri. s. mongolitimonae, Ri. slovaca, Ri. raoultii, Ri. monacensis, and Ri. hoogstraalii); two Borrelia burgdorferi sensu lato spp. (Bo. afzelii and Bo. lusitaniae); two unnamed Hepatozoon spp.; Theileria annulata; and Hemolivia mauritanica. This provided evidence for the natural transstadial survival of these tick-borne microorganisms in adult ticks (in addition a nymph) of Turkey. Surprisingly, this study determined the presence of five different microorganisms (Ba. crassa, Ba. rossi, Babesia sp. Ucbas, Hepatozoon sp., and Ri. hoogstraalii) in host-seeking Haemaphysalis parva adults, for which poor data exist on its vectorial competence. Therefore, this study provides important data indicating the potential vectorial capacity of Ha. parva. This study also revealed the presence of the close ecological and evolutionary relationships between two important vector ticks, Hyalomma marginatum and Hy. aegyptium and determined genetic variations (distinct phylogenetic divergences inside the main clades) in some pathogenic SFG rickettsiae that are found in these ticks. Additionally, the presence of two Babesia species described very recently in hares with unknown vectors, namely Babesia sp. tavsan1 and Babesia sp. tavsan2, were detected for the first time in ticks. Finally, two unnamed Hepatozoon spp. were detected in Haemaphysalis ticks and their phylogenetic positions were demonstrated. Consequently, this study provides important data on the diversity of tick-borne microorganisms in host-seeking ticks and on potentially novel microorganisms (Babesia and Hepatozoon species) and their possible vectors (Ha. parva, Ha. sulcata, Hy. aegyptium, Hy. marginatum, and Rh. turanicus).
... A positive result based on PCR, therefore, does not necessarily mean that the tick species is a vector of the pathogen (Estrada-Peña et al. 2013). To be considered a vector, a tick species must: feed on infectious vertebrates; be able to acquire the pathogen during the blood meal; maintain and multiply it through one or more life stages (transstadial and/or transovarial passage); and pass it on to other host when feeding again (Kahl et al. 2002). Molecular methods are powerful methods but only additional to classical ones based on morphological, serological and clinical studies, as well as studies based on circumstantial (e.g. ...
The objective of the present study was to detect the chosen nucleotide DNA or RNA sequences of the pathogens in ticks of domestic and wild animals of Kerala, South India based on molecular techniques. Among 602 ticks collected, 413 were from bovines (cattle and buffalo), 26 from goats, 101 from dogs and 62 from wild animals. Amblyomma integrum, Am. gervaisi, Dermacentor auratus, Haemaphysalis bispinosa, Ha. intermedia, Ha. shimoga, Ha. spinigera, Rhipicephalus annulatus, Rh. microplus, Rh. haemaphysaloides and Rh. sanguineus s.l. were identified from various domestic and wild animals of Kerala. The cDNA synthesized from the RNA isolated from fully or partially engorged adult female/nymphal ticks was used as template for the specific polymerase chain reactions (PCR). Out of 602 ticks examined, nucleotide sequences of pathogens were detected in 28 ticks (4.65%). The nucleotide sequences of tick-borne pathogens like Theileria orientalis, Babesia vogeli, Hepatozoon canis, Anaplasma marginale, An. bovis, Rickettsia sp. closely related to Ri. raoultii, Ri. massiliae, Ri. africae and Ri. slovaca were detected. The identification of the previously unreported nucleotide sequences of rickettsial pathogens from India is of particular interest due to their zoonotic significance. The phylogenetic analysis of the major piroplasm surface protein (MPSP) gene of T. orientalis amplified from Rh. annulatus ticks revealed that they were genetically close to type 7, which belong to the highly pathogenic Ikeda group.
... This is a function of both the number of larvae fed and the prevalence of B. burgdorferi s.l. in hosts during the previous year. The most common way to estimate the contribution of a given host species or group to the disease hazard is to use the estimated population size of each species/group multiplied by the mean estimated tick load [35,36]. The latter is the total tick load found on infested and non-infested birds divided by the total number of birds sampled. ...
Many vector-borne diseases are transmitted through complex pathogen-vector-host networks, which makes it challenging to identify the role of specific host groups in disease emergence. Lyme borreliosis in humans is now the most common vector-borne zoonosis in the Northern Hemisphere. The disease is caused by multiple genospecies of Borrelia burgdorferi sensu lato bacteria transmitted by ixodid (hard) ticks, and the major host groups transmit Borrelia genospecies with different pathogenicity, causing variable clinical symptoms in humans. The health impact of a given host group is a function of the number of ticks it infects as well as the pathogenicity of the genospecies it carries. Borrelia afzelii, with mainly small mammals as reservoirs, is the most common pathogen causing Lyme borreliosis, and it is often responsible for the largest proportion of infected host-seeking tick nymphs in Europe. The bird-borne Borrelia garinii, though less prevalent in nymphal ticks, is more likely to cause Lyme neuroborreliosis, but whether B. garinii causes disseminated disease more frequently has not been documented. Based on extensive data of annual disease incidence across Norway from 1995 to 2017, we show here that 69% of disseminated Lyme borreliosis cases were neuroborreliosis, which is three times higher than predicted from the infection prevalence of B. garinii in host-seeking ticks (21%). The population estimate of migratory birds, mainly of thrushes, explained part of the annual variation in cases of neuroborreliosis, with a one-year time lag. We highlight the important role of the genospecies' pathogenicity and the host associations for understanding the epidemiology of disseminated Lyme borreliosis.
... In certain TBEV-endemic areas where I. persulcatus and I. ricinus are absent or few in number, other ixodid tick species may act as a TBEV vectors, including proven vector -Haemaphysalis concinna Koch, 1844 (Hoogstraal, 1966;Kozuch and Nosek, 1980;Voshchakina, 1954), and possible vectors -Ixodes pavlovskyi Pom., 1946(Rar et al., 2017Romanenko and Kondrat'eva, 2011), Ixodes ovatus Neumann, 1899 (Takeda et al., 1998), Haemaphysalis longicornis Neumann, 1901, Haemaphysalis flava Neumann, 1897, and Ixodes nipponensis Kitaoka & Saito, 1967(Yun et al., 2012. However, without proven transmission capability, the vector competence of these species of ticks is still under discussion (Kahl et al., 2002). ...
The most significant processes of arbovirus evolution can be expected to occur in the territories where ticks of different species cohabitate and at the boundaries of viruses’ areas, where the probability of the appearance of new virus variants is high due to the possible shift in the main vectors and/or vertebrate hosts. One of the most interesting regions in this regard is the Republic of Tuva. Since most of its territory is covered by mountain ranges and intermountain basins, we were able to study the distribution of vectors and viruses in geographically isolated areas at different altitudes and in various landscapes. From 2008 to 2017, we conducted six expeditions to Tuva and collected 3,077 adult ticks and 24 nymphs. The distribution of tick species was confined to specific landscapes, as follow: Dermacentor nuttalli occurred in steppes, D. silvarum inhabited forest-steppe areas, and Ixodes persulcatus inhabited mixed forests. All three species of ticks were collected on plains and mountain slopes. The range of D. silvarum was shown to be lower than 1300 m above sea level (a.s.l.). Only D. nuttalli and I. persulcatus were collected at higher altitudes. According to our observations, single nymphs of D. nuttalli appear on animals one month before larvae appear. This finding confirms the hypothesis that the immature forms of D. nuttalli are able to overwinter under favourable conditions. We isolated 9 strains and 3 isolates of tick-borne encephalitis virus (TBEV) from I. persulcatus, one strain from D. nuttalli and one strain from D. silvarum. The TBEV strain from D. nuttalli was isolated from the territory inhabited only by Dermacentor ticks. All isolated strains belong to the Siberian subtype of TBEV. TBEV was detected in ticks from all the investigated altitudes. There were no statistically significant differences in the virus prevalence between the Dermacentor and Ixodes ticks. The results of our work provide additional support for the hypothesis of the existence of TBEV foci in areas with an absolute dominance of D. nuttalli.
... In addition, even if transmission occurs, an infection in the vertebrate host does not always develop ( Pfäffle et al. 2015). Therefore, caution is advised when interpreting published data that rely only on DNA detection of microorganisms in ticks ( Kahl et al. 2002). A variety of known or suspected human pathogens have been reported from continental Southeast Asia, as shown in Table 5. ...
Knowledge of the tick fauna of continental Southeast Asia is either patchy or, in some cases, for example Cambodia and Myanmar, poor. Nevertheless, 97 species have been recorded from this region, making it one of the most diverse for ticks worldwide. Throughout Southeast Asia, work on tick-borne diseases of stock and companion animals, as well as of humans, is in its infancy, and the medical, veterinary and socio-economic importance of these diseases is largely unknown. Here we review current knowledge of Southeast Asian ticks and tick-borne diseases, with the aim of stimulating further research on this subject.
... Without proven transmission capability, the vector function of a given tick species for a given pathogen is not substantiated (Kahl et al., 2002). For some pathogens experimental transmission studies were conducted with H. concinna. ...
The ixodid tick Haemaphysalis concinna Koch, 1844 is a proven vector of tick-borne encephalitis (TBE) virus and Francisella tularensis, the causative agent of tularaemia. In the present study, up-to-date maps depicting the geographical distribution and climate adaptation of H. concinna are presented. A dataset was compiled, resulting in 656 georeferenced locations in Eurasia. The distribution of H. concinna ranges from the Spanish Atlantic coast to Kamchatka, Russia, within the belt of 28-64° N latitude. H. concinna is the second most abundant tick species after Ixodes ricinus collected from birds, and third most abundant tick species flagged from vegetation in Central Europe. To investigate the climate adaptation of H. concinna, the georeferenced locations were superimposed on a high-resolution map of the Köppen-Geiger climate classification. A frequency distribution of the H. concinna occurrence under different climates shows three peaks related to the following climates: warm temperate with precipitation all year round, boreal with precipitation all year round and boreal, winter dry. Almost 87.3 % of all H. concinna locations collected are related to these climates. Thus, H. concinna prefers climates with a warm and moist summer. The remaining tick locations were characterized as cold steppes (6.2%), cold deserts (0.8%), Mediterranean climates (2.7%) or warm temperate climates with dry winter (2.9%). In those latter climates H. concinna occurs only sporadically, provided the microclimate is favourable. Beyond proven vector competence pathogen findings in questing H. concinna are compiled from the literature.
... However, studies reporting RF borreliae DNA in tick should be interpreted with caution given the fact that DNA traces found in a tick are not necessarily synonymous with vector competence. The proof of concept for vector specificity lies in the vector competence assays (Kahl et al., 2002). ...
Relapsing fever still remains a neglected disease and little is known on its reservoir, tick vector and physiopathology in the vertebrate host. The disease occurs in temperate as well as tropical countries. Relapsing fever borreliae are spirochaetes, members of the Borreliaceae family which also contain Lyme disease spirochaetes. They are mainly transmitted by Ornithodoros soft ticks, but some species are vectored by ixodid ticks. Traditionally a Borrelia species is associated with a specific vector in a particular geographical area. However, new species are regularly described, and taxonomical uncertainties deserve further investigations to better understand Borrelia vector/host adaptation. The medical importance of Borrelia miyamotoi, transmitted by Ixodes spp., has recently spawned new interest in this bacterial group. In this review, recent data on tick-host-pathogen interactions for tick-borne relapsing fevers is presented, with special focus on B. miyamotoi.
... However, the vector competence of the tick species identified in our study has not been experimentally assessed. Consequently, we cannot assure a classic vector role for any of them and can only call them Cb-carrier ticks (Kahl et al., 2002). On the other hand, the ability of a tick to transmit this bacterium in nature −the vector capacity-depends on several other factors, such as tick population density, host preference, biting rate and perhaps other ecological constraints. ...
Ruminant livestock is the main reservoir of Coxiella burnetii (Cb), but little is known about the role of wildlife and ticks in its epidemiology. The Iberian ibex (Capra pyrenaica, Schinz 1838) population of "Ports de Tortosa i Beseit" (NE Spain) suffers intense tick infestations and low reproduction rates. This study aims to (1) assess the relationship between infection in ibexes (detection of serum antibodies and/or of Cb DNA in tissues) and Cb DNA presence in ticks hosted by the same ibexes; and (2) identify Cb associated risk factors. Between 2011 and 2015, serum (n = 130), spleen (n = 72), lymph node (n = 89) and tick (n = 669) samples from 134 hunter-harvested ibexes were collected. Antibody detection was performed by ELISA and Cb DNA presence was assessed by PCR. Potential risk factors were assessed with regression tree models. Although 30% of the ibexes (39/130; 95%CI, [10%-29.8%]) had antibodies, Cb DNA was detected in only 9.8% of the ibexes (11/112; 95%CI [7.6%-27.25%]). The prevalence of Cb-carrier ticks averaged 10% and exceeded 20% for the genus Haemaphysalis. However, lacking correlation between infection in ibexes and their ticks does not support tick-to-ibex transmission or vice versa. Tree modelling points to host, population and environmental factors as drivers of Cb infection in ticks and suggests connections with the domestic cycle. The percentage of Cb-carrier ticks detected is noteworthy. Along with heavy tick infestations, it suggests vector potential for these tick species, especially for the genera Rhipicephalus and Haemaphysalis. Since vector competence has not been assessed in these tick species, a classic vector role cannot be proposed nor discarded, but promoter factors of vector capacity occur. In addition, the risk of tick-borne infection through tick excreta should not be neglected. While the airborne route is the preeminent route for Cb infection, ticks' contribution to Cb epidemiology deserves further attention.
... The detection of the pathogen nucleic acid in a feeding tick indicates that it possesses the carrier status (Estrada-Pena et al., 2013). In order to conclude that a tick is a vector, more detailed experimental studies are required to determine the vector competence of this tick species (Kahl et al., 2002). On the other hand, human CCHF case has not yet been reported from Buğra (MoH, 2016). ...
In Turkey, Crimean-Congo hemorrhagic fever (CCHF) outbreaks started in northern regions in 2002. Human cases still continue to increase and the disease spreads in many other provinces of Turkey. The ecological role of the vector tick species occurring in Turkey is not certain exactly. Therefore, we planned a broad range tick study in three different ecological and geographical areas extending from the West Black Sea regions down to the Central Anatolia. The aim of this study was to determine and characterize CCHFV molecularly in feeding-ticks collected from various wild and domestic animals and from humans as well as in questing and unfed ticks. In this study, 4283 tick samples derived from 21 tick species were collected from 76 villages and 10 central districts in total. All tick pools were screened for the presence of CCHFV RNA by two nested RT-PCRs. PCR assays were positive for 27 (3.6%) of 736 pools. CCHFV was detected in Hyalomma marginatum, Dermacentor marginatus, Rhipicephalus bursa, Rhipicephalus turanicus, Hyalomma excavatum and Haemaphysalis parva pools. As a result of the phylogenetic analysis, it was determined that the obtained CCHFV sequences are clustered into Europe 1 clade. CCHFV was detected among ticks obtained from cattle, goats, wild boar, hare, and the ground. The presence of CCHFV in ticks obtained from various domestic and wild hosts and the nature, and thereby the distribution patterns of the virus in different ecological areas were presented in this study. Furthermore, CCHFV was also detected in unusual tick species. Consequently, these results indicate that tick surveillance studies in large-scale and wide varieties contribute to the ecology and epidemiology of CCHF in that region, and can be used as an early-warning system.
... Another approach is to assay attached I. scapularis larvae for the bacterium. As vertical transmission of B. burgdorferi is rare or nonexistent in I. scapularis (Piesman et al. 1986, Patrican 1997, Kahl et al. 2002, Rollend et al. 2013, larvae are largely assumed to be uninfected upon hatching. The transmission cycle of B. burgdorferi begins when larval ticks acquire the pathogen by ingesting blood from an infected host. ...
Measuring rates of acquisition of the Lyme disease pathogen, Borrelia burgdorferi sensu lato Johnson, Schmid, Hyde, Steigerwalt & Brenner, by the larval stage of Ixodes scapularis Say is a useful tool for xenodiagnoses of B. burgdorferi in vertebrate hosts. In the nymphal and adult stages of I. scapularis, the duration of attachment to hosts has been shown to predict both body engorgement during blood feeding and the timing of infection with B. burgdorferi. However, these relationships have not been established for the larval stage of I. scapularis. We sought to establish the relationship between body size during engorgement of larval I. scapularis placed on B. burgdorferi-infected, white-footed mice (Peromyscus leucopus Rafinesque) and the presence or absence of infection in larvae sampled from hosts over time. Body size, time, and their interaction were the best predictors of larval infection with B. burgdorferi. We found that infected larvae showed significantly greater engorgement than uninfected larvae as early as 24 h after placement on a host. These findings may suggest that infection with B. burgdorferi affects the larval feeding process. Alternatively, larvae that engorge more rapidly on hosts may acquire infections faster. Knowledge of these relationships can be applied to improve effective xenodiagnosis of B. burgdorferi in white-footed mice. Further, these findings shed light on vector-pathogen-host interactions during an understudied part of the Lyme disease transmission cycle.
... Additionally, Table 3 provides a summary on frequent pathogen findings in adult questing D. reticulatus ticks without proven vector function and Table 4 summarises the results of three experimental transmission studies, again representative for D. reticulatus. Without proven transmission capability vector function of a given tick species for a given pathogen is not (Kahl et al., 2002). Mere demonstration of the carrier status of field-collected ticks is only the very first step to prove vector competence. ...
The ornate dog tick Dermacentor reticulatus is vector of several blood parasites, including Babesia canis, a causative agent of babesiosis. The geographical range of D. reticulatus in Europe is discontinuous with a gap separating eastern and western macroregions. New foci observed in several locations in western and central Europe were considered an expansion of the western population, including foci in western Poland. In the present paper we used molecular markers to identify the origins of these foci, and we compared their genetic polymorphism to D. reticulatus collected in sites situated within the eastern population. The overall polymorphism in mt 16S rDNA was low, and all sites from the western population shared the same haplotype suggesting the expansion in this area. In the marker 5.8S- ITS2 rDNA we found no differences in polymorphism between sites from eastern Poland (eastern population), and newly emerged foci in western Poland considered a putative expansion zone of the western population. However, the sites from western Poland differed considerably from nearby German site. Our results show that foci in western Poland could not have originated from D. reticulatus from the western population, as previously thought. We found that the state border following river hinders considerably gene flow between adjacent sites what suggest that natural dispersal of D. reticulatus by wildlife is unlikely, and the emergence of new foci should rather be contributed to human-associated dispersal. We propose that livestock, and pets travelling with their owners are the most probable source of new foci, and they can easily transfer ticks within a country but not between countries.
... Reservoir hosts are proven natural hosts of vector ticks, and ticks may become infected while feeding on these animals ( Kahl et al. 2002). Distinct genospecies of B. burgdorferi s.l. are associated with different reservoir hosts ( Hanincová et al. 2003a, 2003b, Humair et al. 1995, Kurtenbach et al. 1998a, 1998b). ...
Borrelia burgdorferi sensu lato (s.l.) is the most abundant tick-borne pathogen of the northern hemisphere, and the causative agent of Lyme borreliosis (LB). LB occurs all over Europe, where conditions are suitable for tick survival and competent reservoir hosts species are abundant. The geographical distribution of B. burgdorferi s.l. genospecies in Europe can differ even over relatively small areas as well as over time period. Several host species contribute in the epidemiology of LB such as rodents, lizards and wild or domestic herbivores and carnivores. Lacertid lizards and medium-sized mammals such us squirrels, hedgehogs and mustelid species can live in close proximity to human dwellings and can have important role in the urban and natural cycle of the B. burgdorferi sensu lato spirochaetes. These vertebrate species can harbour Ixodes ricinus or Ixodes hexagonus the main vector species of B. burgdorferi and some of them could live also in highly urbanised habitats. We also present the collected data about presence of Lyme spirochaetes in tissue and ticks removed from these hosts. In this chapter we would like to focus on the role of these often neglected host species through available data about geographical distribution, ecology and epidemiological studies, and highlight the public health relevance of these hosts in rural and urban environment.
Borrelia burgdorferi sensu lato (s.l.) is the most abundant tick-borne pathogen of the northern hemisphere, and the causative agent of Lyme borreliosis (LB). LB occurs all over Europe, where conditions are suitable for tick survival and competent reservoir hosts species are abundant. The geographical distribution of B. burgdorferi s.l. genospecies in Europe can differ even over relatively small areas as well as over time period. Several host species contribute in the epidemiology of LB such as rodents, lizards and wild or domestic herbivores and carnivores. Lacertid lizards and medium-sized mammals such us squirrels, hedgehogs and mustelid species can live in close proximity to human dwellings and can have important role in the urban and natural cycle of the B. burgdorferi sensu lato spirochaetes. These vertebrate species can harbour Ixodes ricinus or Ixodes hexagonus the main vector species of B. burgdorferi and some of them could live also in highly urbanised habitats. We also present the collected data about presence of Lyme spirochaetes in tissue and ticks removed from these hosts. In this chapter we would like to focus on the role of these often neglected host species through available data about geographical distribution, ecology and epidemiological studies, and highlight the public health relevance of these hosts in rural and urban environment.
... Compared with abundance of host-seeking nymphs alone, the abundance of host-seeking infected nymphs is a better predictor of Lyme disease incidence (Pepin et al. 2012). The abundance of infected host-seeking nymphs has been expressed in different ways, including the number of infected host-seeking nymphs collected per unit area sampled (in which case it also can be referred to as the density of infected host-seeking nymphs), the number of infected host-seeking nymphs collected per unit of active sampling time, and the average distance of sampling resulting in the encounter with one infected nymph (Kahl et al. 2002, Estrada-Peña et al. 2013. As efforts to estimate the abundance or density of infected host-seeking nymphs within a given sampling area typically are based on a limited number of sampling occasions, they will contact only a portion of the total population of nymphs present within that area even if the entire area is sampled (Daniels et al. 2000). ...
The nymphal stage of the blacklegged tick, Ixodes scapularis Say, is considered the primary vector to humans in the eastern United States of the Lyme disease spirochete Borrelia burgdorferi sensu stricto. The abundance of infected host-seeking nymphs is commonly used to estimate the fundamental risk of human exposure to B. burgdorferi, for the purpose of environmental risk assessment and as an outcome measure when evaluating environmentally based tick or pathogen control methods. However, as this tick-based risk measure does not consider the likelihoods of either human encounters with infected ticks or tick bites resulting in pathogen transmission, its linkage to the occurrence of Lyme disease cases is worth evaluating. In this Forum article, we describe different tick-based risk measures, discuss their strengths and weaknesses, and review the evidence for their capacity to predict the occurrence of Lyme disease cases. We conclude that: 1) the linkage between abundance of host-seeking B. burgdorferi-infected nymphs and Lyme disease occurrence is strong at community or county scales but weak at the fine spatial scale of residential properties where most human exposures to infected nymphs occur in Northeast, 2) the combined use of risk measures based on infected nymphs collected from the environment and ticks collected from humans is preferable to either one of these risk measures used singly when assessing the efficacy of environmentally based tick or pathogen control methods aiming to reduce the risk of human exposure to B. burgdorferi, 3) there is a need for improved risk assessment methodology for residential properties that accounts for both the abundance of infected nymphs and the likelihood of human-tick contact, and 4) we need to better understand how specific human activities conducted in defined residential microhabitats relate to risk for nymphal exposures and bites.
... This evaluation is acknowledged to be an assessment of " risk " by the tick, something that has an immediate spatial meaning. However, risk from ticks and the pathogens they transmit is the result of a complex equation derived from the climate itself, the availability and abundance of some key hosts (maintenance hosts, carrier hosts, and reservoir hosts, according to the terminology by Kahl et al., 2002), the physical features of the habitat (Estrada-PeñaPe˜Peña, 2003), and the social factors operating at the ecosystem level (Randolph, 2009; Semenza et al., 2010). Researchers working on the estimation of risk from medically relevant arthropods may be unaware of the explosion of work addressing important but mostly methodological issues, like sensitivity of models to the number of occurrence records, the ratio of presences to absences (Valverde and Lobo, 2006), the grain of the environmental layers (), and other technical points (Peterson et al., 2008). ...
There is a growing interest in inferring the associations of health-threatening arthropods to capture the climate niche to which they associate, projecting such inference on a territory. This is intended to predict the range of distribution of the tick and to understand their responses to climate scenarios, using the so-called correlative models. However, some methodological gaps might prevent to obtain an adequate background against which test hypotheses. We explore, describe and illustrate these procedural inaccuracies with examples focused on the tick Ixodes ricinus, and how these may affect the modelling outcomes. We aim to provide a background of rules against which develop reliable models for these parasites. The use of partial sets of occurrences of the tick might produce unreliable associations with climate because the algorithms cannot capture the complete niche to which the tick is associated. Reliability measures of the model cannot detect these inaccuracies, and undesirable estimations of the niche will prevail in the chain of further calculations. The use of inadequate environmental variables (covariates) may lead to inflation of the results of the model through two statistical processes, called autocorrelation and colinearity. The high colinearity existing in climate products derived from interpolation of climate recording stations is demonstrated, and it is explicitly advised the training of climate models with satellite-derived information of climate, of which colinearity of the time series has been removed through a harmonic regression. The high uncertainty if inference on the climate niche is applied into different time slices, like projected climate scenarios is also pointed in the results.
... Additionally, Table 3 provides a summary on frequent pathogen findings in adult questing D. reticulatus ticks without proven vector function and Table 4 summarises the results of three experimental transmission studies, again representative for D. reticulatus. Without proven transmission capability vector function of a given tick species for a given pathogen is not (Kahl et al., 2002). Mere demonstration of the carrier status of field-collected ticks is only the very first step to prove vector competence. ...
The goal of this paper is to present up-to-date maps depicting the geographical distribution of Dermacentor species in Europe based on georeferenced sampling sites. Therefore, a dataset was compiled, resulting in 1,286 D. marginatus (Sulzer, 1776) and 1,209 D. reticulatus (Fabricius, 1794) locations. Special emphasis is given to the region of the European Alps depicting a presumable climate barrier of the mountains and to overlaps in the distribution of both species as well as on the situation in eastern European countries. For the latter newly described Dermacentor findings comprise 59 locations in Romania and 62 locations in Ukraine. The geographical distributions of both species in Europe range from Portugal to Ukraine (and continue to the east of Kazakhstan). Although it is well known that D. marginatus is adapted to a warmer and drier climate at more southern latitudes and D. reticulatus to a moderately moist climate at more northern latitudes, the distribution limits of both species were not well known. Here, the northern and southern distribution limits for both species in Europe, as determined from the georeferenced database, were specified for D. marginatus by the belt of 33 - 51∘ N latitude and for D. reticulatus by the belt of 41 - 57∘ N latitude. Thus, overlapping species distributions were found between 41∘ N and 51∘ N.
... To prove birds as reservoirs of tick-borne pathogens of the genus Rickettsia is not easy. A reservoir host is defined by its capacity to infect ticks feeding on it (Kahl et al. 2002). One method that helps to identify reservoirs in nature is the comparison of infection rates in questing larvae and nymphs with larvae fed on the suspected host in the same habitat. ...
Ixodid ticks (Acari: Ixodidae) are known as primary vectors of many pathogens causing diseases in humans and animals. Ixodes ricinus is a common ectoparasite in Europe and birds are often hosts of subadult stages of the tick. From 2012 to 2013, 347 birds belonging to 43 species were caught and examined for ticks in three sites of Slovakia. Ticks and blood samples from birds were analysed individually for the presence of Rickettsia spp. and Coxiella burnetii by PCR-based methods. Only I. ricinus was found to infest birds. In total 594 specimens of bird-attached ticks were collected (451 larvae, 142 nymphs, 1 female). Altogether 37.2 % (16/43) of bird species were infested by ticks and some birds carried more than one tick. The great tit, Parus major (83.8 %, 31/37) was the most infested species. In total, 6.6 and 2.7 % of bird-attached ticks were infected with Rickettsia spp. and C. burnetii, respectively. Rickettsia helvetica predominated (5.9 %), whereas R. monacensis (0.5 %) was only sporadically detected. Coxiella burnetii was detected in 0.9 %, Rickettsia spp. in 8.9 % and R. helvetica in 4.2 % of bird blood samples. The great tit was the bird species most infested with I. ricinus, carried R. helvetica and C. burnetti positive tick larvae and nymphs and was found to be rickettsaemic in its blood. Further studies are necessary to define the role of birds in the circulation of rickettsiae and C. burnetii in natural foci.
... This evaluation is acknowledged to be an assessment of " risk " by the tick, something that has an immediate spatial meaning. However, risk from ticks and the pathogens they transmit is the result of a complex equation derived from the climate itself, the availability and abundance of some key hosts (maintenance hosts, carrier hosts, and reservoir hosts, according to the terminology by Kahl et al., 2002), the physical features of the habitat (Estrada-Peña , 2003), and the social factors operating at the ecosystem level (Randolph, 2009; Semenza et al., 2010). ...
... Currently, a large number of new, emerging and re-emerging diseases are zoonotic and many of them are transmitted by arthropod vectors, including ticks. Under these conditions acknowledging host associations of ticks is useful in identifying the different bridging hosts ( Kahl et al., 2001), which may form a link between distinct enzootic cycles of infection in particular regions, as well as those hosts that pose a threat to human health by their mere vicinity to human habitations.The distribution maps may be biased due to pre-selection of sampling sites by collectors, or be representative of locations at which collectors reside or work. Also, regarding host associations, the results may be biased by the ease of tick sampling from domestic animals as well as by the immediate economic interest regarding livestock. ...
Tick Species (Acari: Ixodoidea) Distribution, Seasonality and Host Associations in Romania
By integrating the literature data with those derived from personal investigations, the authors present the distribution of the 27 tick species (25 ixodids and 2 argasids) identified up to now in Romania, as well as some aspects regarding their abundance, seasonality and host associations. Altogether, 1439 tick records (of which 256, covering 25 counties, belong to the authors themselves) were georeferenced using EpiMap (an ArcView®-compatible GIS) from CDC's EpiInfo™ software package (v. 3.5.1), on a level 2 LAU (Local Administrative Units) shapefile. The resultant distribution maps and the data on seasonality and host associations may prove to be a useful reference system for subsequent studies on different tick species' distribution, ecology and biology, as well as a predictive tool for human and veterinary medicine, bearing in mind the vectorial role that ticks play in some dangerous diseases for man and livestock.
The tick Ixodes ricinus is the most important vector species of infectious diseases in European France. Understanding its distribution, phenology, and host species use, along with the distribution and prevalence of associated pathogens at a national scale is essential for developing prevention strategies. The aim of this paper is to provide a systematic map and narrative review of the existing knowledge on the eco-epidemiology of I. ricinus in France. Using literature published up to 2020, the present paper provides a distribution map for the species and a summary of environmental factors explaining observed geographical differences in phenology and temporal differences in abundance. The diversity of vertebrate host species used by this tick, along with their degree of infestation when available, are presented and discussed with respect to their potential contribution to the population dynamics of I. ricinus and the circulation of tick-borne zoonotic pathogens. Prevalence data of detected pathogens are summarised in different maps. Results from 187 identified references show that the species is present in most departments, but scarce under Mediterranean climates and in coastal habitats. Its phenology is generally bimodal with climate-associated variations. Abundance seems positively influenced by forest cover and host abundance. Rodents and ruminants are the most studied species groups, but the diversity of sampling protocols (e.g., location, season, exhaustivity of inspection) precluded direct comparisons between groups. Data on pathogens are patchy, with most studies conducted near research laboratories. Among pathogens, Borrelia burgdorferi sensu lato is the most examined and seems most prevalent in northeastern and central France. The review highlights the gaps in our knowledge of tick-host-pathogen interactions, their ecologies and their distributions, and demonstrates the need to address these gaps in order to optimize tick and tick-borne diseases prevention and control.
Background
Understanding how study design and monitoring strategies shape inference within, and synthesis across, studies is critical across biological disciplines. Many biological and field studies are short term and limited in scope. Monitoring studies are critical for informing public health about potential vectors of concern, such as Ixodes scapularis (black-legged ticks). Black-legged ticks are a taxon of ecological and human health concern due to their status as primary vectors of Borrelia burgdorferi , the bacteria that transmits Lyme disease. However, variation in black-legged tick monitoring, and gaps in data, are currently considered major barriers to understanding population trends and in turn, predicting Lyme disease risk. To understand how variable methodology in black-legged tick studies may influence which population patterns researchers find, we conducted a data synthesis experiment.
Materials and Methods
We searched for publicly available black-legged tick abundance dataset that had at least 9 years of data, using keywords about ticks in internet search engines, literature databases, data repositories and public health websites. Our analysis included 289 datasets from seven surveys from locations in the US, ranging in length from 9 to 24 years. We used a moving window analysis, a non-random resampling approach, to investigate the temporal stability of black-legged tick population trajectories across the US. We then used t-tests to assess differences in stability time across different study parameters.
Results
All of our sampled datasets required 4 or more years to reach stability. We also found several study factors can have an impact on the likelihood of a study reaching stability and of data leading to misleading results if the study does not reach stability. Specifically, datasets collected via dragging reached stability significantly faster than data collected via opportunistic sampling. Datasets that sampled larva reached stability significantly later than those that sampled adults or nymphs. Additionally, datasets collected at the broadest spatial scale (county) reached stability fastest.
Conclusion
We used 289 datasets from seven long term black-legged tick studies to conduct a non-random data resampling experiment, revealing that sampling design does shape inferences in black-legged tick population trajectories and how many years it takes to find stable patterns. Specifically, our results show the importance of study length, sampling technique, life stage, and geographic scope in understanding black-legged tick populations, in the absence of standardized surveillance methods. Current public health efforts based on existing black-legged tick datasets must take monitoring study parameters into account, to better understand if and how to use monitoring data to inform decisioning. We also advocate that potential future forecasting initiatives consider these parameters when projecting future black-legged tick population trends.
Ticks are hematophagous arthropods that can transmit, while they are feeding on hosts, microorganisms that can cause diseases in humans or animals. The best known and most studied bacteria are Borrelia burgdorferi sensu lato (s.l.), the causative agent of Lyme borreliosis. Along with B. burgdorferi s.l., ticks can harbor many microorganisms. In this chapter, we review some ecological, epidemiological, and clinical aspects of the main microorganisms, apart from B. burgdorferi s.l., known to be transmitted by ixodes ticks in Europe and pathogenic for humans: B. miyamotoi, Anaplasma phagocytophilum, Candidatus Neoehrlichia mikurensis, Rickettsia monacensis, Rickettsia helvetica, Francisella tularensis, human babesiosis agents, and the ixodid-borne flaviviruses. finally, we discuss scientifically established facts about human co-infections.KeywordsTick-borne diseases
Ixodes
Anaplasma
Borrelia miyamotoi
Candidatus Neoehrlichia mikurensis
Rickettsia helvetica
Francisella tularensis
TBEFlaviviruses
Identifying the key vector and host species that drive the transmission of zoonotic pathogens is notoriously difficult but critical for disease control. We present a nested approach for quantifying the importance of host and vectors that integrates species' physiological competence with their ecological traits. We apply this framework to a medically important arbovirus, Ross River virus (RRV), in Brisbane, Australia. We find that vertebrate hosts with high physiological competence are not the most important for community transmission; interactions between hosts and vectors largely underpin the importance of host species. For vectors, physiological competence is highly important. Our results identify primary and secondary vectors of RRV and suggest two potential transmission cycles in Brisbane: an enzootic cycle involving birds and an urban cycle involving humans. The framework accounts for uncertainty from each fitted statistical model in estimates of species' contributions to transmission and has has direct application to other zoonotic pathogens.
Dans le cadre du plan national de prévention et de lutte contre la maladie de Lyme et les maladies transmissibles par les tiques (« Plan Lyme »)1, lancé en 2016, un projet de recherche bibliographique sur l’écologie, la surveillance et la lutte contre les tiques présentes en France métropolitaine et responsables de maladies infectieuses humaines zoonotiques dont la borréliose de Lyme, a été commandité à l’ANSES par la Direction Générale de la Santé. Ce projet a été confié à l’École nationale vétérinaire d’Alfort dans le cadre d’une Convention de Recherche et Développement (CRD). Pour le mener à bien, un post-doctorant a été recruté sur un contrat d’un an et un mois (du 14 octobre 2019 au 13 novembre 2020) au sein de l’UMR BIPAR (EnvA – ANSES – INRAE).
Full text available at: https://hal.archives-ouvertes.fr/anses-03263410/
Ticks are vectors and, more interesting, ectoparasites that cause significant economic loss to livestock and adversely affect livestock hosts in several ways. The study was taken out in the Bugudanahalli village of Tumkur district, Karnataka, from February to April. It was found that the tick load is increased because of the availability of favorable conditions (an agro-climatic region with an annual rainfall of 592.9 to 900mm), which led to embryonic development and increased larval activity for the infestation in cattle. The study was carried out to assess the infestation of ticks on different anatomical regions of these two breeds. The necessary data collected during the survey is recorded separately for each week to analyze the result statistically using datasheets. For the ticks per animal, the factors considered were tick genera, cattle breed, cattle anatomy region, the severity of ticks, etc. In the present study, 1324 ticks were collected from both the cattle breeds, and the two identified tick genera are Haemaphysalis and Rephicephalus (Boophilus). The severity of tick load in various anatomical regions of these two breeds varied significantly. Holstein Friesian is more infested when compared to Jersey breed due to its less resistance to the infestation of ticks. This study suggests the farmers and livestock owners in selecting the tick-resistant cattle; age-wise, breed-wise, and season-wise.
There are various arthropods (e.g. insects, chiggers, mites, ticks) that take one or more blood meals on terrestrial vertebrates in the course of their lifetime. Among them are ixodid ticks (Acari, Ixodidae), all of which are obligately hematophagous. Their parasitic lifestyle predestines them to act as transmitters or vectors of microparasites, often pathogenic to humans and/or domestic animals. The list of ixodid tick-borne pathogens is long, encompassing viruses, bacteria, protozoans, and nematodes. The present mini-review gives a brief overview of the most relevant biological attributes that make ixodid ticks very efficient vectors compared with other hematophagous arthropod taxa.
Matrix Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) has been demonstrated to be useful for tick identification at the species level. More recently, this tool has been successfully applied for the detection of bacterial pathogens directly in tick vectors. The present work has assessed the detection of Borrelia burgdorferi sensu lato in Ixodes ricinus tick vector by MALDI-TOF MS. To this aim, experimental infection model of I. ricinus ticks by B. afzelii was carried out and specimens collected in the field were also included in the study. Borrelia infectious status of I. ricinus ticks was molecularly controlled using half-idiosome to classify specimens. Among the 39 ticks engorged on infected mice, 14 were confirmed to be infected by B. afzelii. For field collection, 14.8% (n = 12/81) I. ricinus ticks were validated molecularly as infected by B. burgdorferi sl. To determine the body part allowing the detection of MS protein profile changes between non-infected and B. afzelii infected specimens, ticks were dissected in three compartments (i.e. 4 legs, capitulum and half-idiosome) prior to MS analysis. Highly reproducible MS spectra were obtained for I. ricinus ticks according to the compartment tested and their infectious status. However, no MS profile change was found when paired body part comparison between non-infected and B. afzelii infected specimens was made. Statistical analyses did not succeed to discover, per body part, specific MS peaks distinguishing Borrelia-infected from non-infected ticks whatever their origins, laboratory reared or field collected. Despite the unsuccessful of MALDI-TOF MS to classify tick specimens according to their B. afzelii infectious status, this proteomic tool remains a promising method for rapid, economic and accurate identification of tick species. Moreover, the singularity of MS spectra between legs and half-idiosome of I. ricinus could be used to reinforce this proteomic identification by submission of both these compartments to MS.
Background. In the northern hemisphere, ticks of the Ixodidae family are vectors of diseases such as Lyme borreliosis, Rocky Mountain spotted fever and tick-borne encephalitis. Most of these ticks are generalists and have a three-host life cycle for which they are dependent on three different hosts for their blood meal. Finding out which host species contribute most in maintaining ticks and the pathogens they transmit, is imperative in understanding the drivers behind the dynamics of a disease.
Methods. We performed a systematic review to identify the most important vertebrate host species for Ixodes ricinus and Borrelia burgdorferi s.l. as a well-studied model system for tick-borne diseases. We analyzed data from 66 publications and quantified the relative contribution for 15 host species.
Review results. We found a positive correlation between host body mass and tick burdens for the different stages of I. ricinus. We show that nymphal burdens of host species are positively correlated with infection prevalence with B. burgdorferi s.l., which is again positively correlated with the realized reservoir competence of a host species for B. burgdorferi s.l. Our quantification method suggests that only a few host species, which are amongst the most widespread species in the environment (rodents, thrushes and deer), feed the majority of I. ricinus individuals and that rodents infect the majority of I. ricinus larvae with B. burgdorferi s.l.
Discussion. We argue that small mammal-transmitted Borrelia spp. are maintained due to the high density of their reservoir hosts, while bird-transmitted Borrelia spp. are maintained due to the high infection prevalence of their reservoir hosts. Our findings suggest that Ixodes ricinus and Borrelia burgdorferi s.l. populations are maintained by a few widespread host species. The increase in distribution and abundance of these species, could be the cause for the increase in Lyme borreliosis incidence in Europe in recent decades.
Ticks are prominent parasites and competent vectors of pathogens that affect both humans and animals. This review outlines and illustrates the main features of the morphology of ticks of the families Ixodidae and Argasidae, and summarises the basic components of their life cycles. It focuses mainly on development processes and mortality among tick populations so as to provide an overview of how they are regulated in nature and how pathogens can be transmitted under such a framework. The effects of the weather on these life cycles are reviewed. The author also examines how landscape structure and biotic factors, such as the presence and abundance of hosts, may shape the density of tick populations. The uncertainty inherent in dealing with the transmission of pathogens by ticks is highlighted; this results from the sometimes complex relationships among the vectors, the climate and the presence and density of host populations. The need to obtain reliable field estimations of such relationships before drawing conclusions about the effects of the isolated components of the system is stressed. A section is devoted to addressing the expected (and not yet totally understood) effects of trends in climate on the spread of ticks, and how these can be analysed and tracked.
Lyme borreliosis, a multisystem disorder, is caused by spirochaetes of the Borrelia (B.) burgdorferi sensu lato complex, which are transmitted by ticks. In the last years the disease has become a global public health problem and a prototype of an emerging infection. This review presents a large body of information on cellular and molecular biology of B. burgdorferi , interaction with the human host, immune response and disease pathogenesis.
Ticks (Acari: Ixodoidea) are worldwide prominent pests as haematophagous parasites on humans and do-mestic animals. This paper emphasizing the central European situation, outlines the biology and the medical significan-ce of four tick species which have often succeeded to colonize suburban environments, and describes the ecological cir-cumstances of their occurrence. Tick species found in towns in central Europe are Argas reflexus (Argasidae), and Ixodes ricinus and I. hexagonus (Ixodidae). Rhipicephalus sanguineus, is occasionally transported unrecognized on pet dogs from southern countries to central Europe. A. reflexus was originally a Mediterranean species. Under central European conditions it lives exclusively in human buildings with nearby nesting feral pigeons. If the natural host is not available, hu-mans are bitten. I. ricinus is the main European vector of Borrelia burgdorferi s.l. and the tick-borne encephalitis (TBE) virus. This tick penetrates into towns by colonizing new and old "green islands" in the urban environment, where the microclimatic humidity requirements are met, especially in the permanent leaf-litter of forest stands. Transportation of ticks into towns takes place on mobile vertebrate hosts, probably mainly on birds. I. ricinus adults are exclusively found on mammals. The rarity of these animals in towns, suburban hedgehogs seem to be most important for adult tick fee-ding. Suburban I. ricinus populations are frequently infected with B. burgdorferi and sometimes also with TBE-virus. I. hexagonus parasitizes members of the Carnivora and hedgehogs and is common in suburban locations in central Eu-rope. It spends its non-parasitic phases in the burrows/nests of its hosts. Bites in humans are rare, and it is a proven vector of both B. burgdorferi and TBE virus, and might support the establishment of these agents in the urban environment.
Research conducted on natural enemies of ticks, namely predators, parasitoids and pathogens, is reviewed. Predators include ants, birds, rodents, lizards, shrews, spiders and domestic chickens. All the known parasitoids are hymenopteran wasps belonging to the genera Ixodiphagus and Hunterellus. The work so far done on bacteria, fungi, viruses and rickettsiae which are pathogenic to ticks is reviewed, both with regard to experimental infections and natural infections. The possibilities of using natural enemies as biological control agents of ticks are discussed.
Borrelia burgdorferi, the agent of Lyme borreliosis, is vectored in Europe byIxodes ricinus. In unfed ticks, the spirochaete resides primarily in the midgut, but a low percentage (5.5%; 4/73) of naturally infected ticks may present a systemic infection involving organs such as the salivary glands and central ganglion (Burgdorferet al., 1983).
In this study, we examined 79 unfed nymphs collected in two sites in Switzerland (Neuchâtel and Aarberg), and 35 unfed nymphs which were fed as uninfected larvae on 3 infectedApodemus sylvaticus mice. Dieterle silver staining was used to visualize the spirochaetes in the ticks.
Of the unfed field-collected nymphs, 21/79 (27%) were infected of which 2/21 (10%) had systemic infections. Taking account of the site of collection, we observed that 0/12 ticks from Neuchâtel were systemically infected whereas 2/9 (22%) from Aarberg had a disseminated infection. Out of the 35 unfed nymphs examined after an infectious blood meal on rodents, 14 (40%) were infected and 2 (14%) had a disseminated infection.
A total of 4/35 (11%) unfed infected nymphs presented a systemic infection which represents a higher percentage than previously described. The presence of spirochaetes in salivary glands of systemically infected ticks before the initiation of feeding may reduce the time delay generally recorded for the tick-borne transmission ofB. burgdorferi.
Summary The causative agent of Lyme disease, Borrelia burgdorferi, is transmitted by ticks of the Ixodes ricinus complex. In this study, we report the antibody response of recombinant inbred strains of mice of the H-2, b, d, and k haplotypes, infected with/~ burgdorferi as a result of exposure to infected I. daramini. The patterns of antibody response assayed by Western blot analysis indicate significant major histocompatibility complex (MHC) restriction to bacterial antigens within the first 2 mo of infection in mice. Other bacterial antigens induce a significant response across the MHC haplotypes tested when assayed on the same bacterial strain used to transmit the infection, but do not crossreact with the same proteins derived from heterologous strains of/~ burgdorferi. No response to outer surface protein A was detected at any time during the 60-d period we analyzed this infection. A third group of bacterial antigens appear to generate a MHC-nonrestricted response, and this lack of restriction is maintained when assaying the crossreactivity of the response with other strains of/~ burgdo~ri. These proteins may provide more accurate diagnostic probes than those currently in use. Finally, there appears to be a significant difference in the expression of most bacterial antigens when the spirochete is cultured for many passages since the same strain of bacterium isolated from low-passage and high-passage preparations exhibit different banding patterns in Western blots when assayed with the same sera.
The taiga tick, Ixodes persulcatus, the main vector of tick-borne encephalitis (TBE) virus and the Lyme diseases spirochete, Borrelia burgdorferi, populates southern taiga forests of Russia from the Baltic Sea to the Pacific Ocean. For about thirty years, from the beginning of the 1950s until the end of the 1970s, tick control was the leading strategy of TBE prevention in Russia. Large-scale acaricidal treatment of tick populated forest areas, which were habitually visited by people or where TBE cases regularly occurred, provided effective tick control and, as a result, significant reduction in the number of TBE cases. DDT was found to be the only acaricide which produced complete elimination of the tick populations over the treated areas through a single treatment. During those years, numerous data on various aspects of acaricidal impact on tick populations were obtained, and models of the elimination of tick populations and their subsequent re-establishment were developed. At present, stringent requirements for toxicological characteristics of pesticides and increased public concern about environmental safety make such treatment impossible; moreover, in many cases such treatment would be epidemiologically groundless. The emergence of new tick-borne infections, however, increases the necessity for human protection which in many cases could be most effective through controlling the tick vectors. The practical experience accumulated by Russian scientists may be of great value for the current development of new approaches to the prevention of tick-transmitted diseases.
Questing individuals of Ixodes ricinus (L.) on a naturally infested moorland in Wales were censused every fortnight from January 1981 to October 1982 by blanket-dragging, and feeding ticks were counted on the sheep hosts. The seasonal activity patterns for ticks in all three stages were unimodal, with nymphs and adults active between March and July, and larvae active between April and August. This unimodal, as opposed to the usually described bimodal, pattern is explained in terms of the long cold winters and short summers of this field site. The survival time of questing nymphs was calculated from an analysis of their changing lipid content during the activity season to be a maximum of four months, which is consistent with the other field observations. The precise identification of the pattern of activity, as well as being essential for the application of appropriately timed control procedures, is necessary for the interpretation of the tick-host interactions under various control regimes that were applied.
Borrelia burgdorferi, the spirochete that causes Lyme disease, binds decorin, a collagen-associated extracellular matrix proteoglycan found in the skin (the site of entry for the spirochete) and in many other tissues. Two borrelial adhesins that recognize this proteoglycan, decorin binding proteins A and B (DbpA and DbpB, respectively), have recently been identified. Infection of mice by low-dose B. burgdorferi challenge elicited antibodies against DbpA and DbpB that were sustained at high levels, suggesting that these antigens are expressed in vivo. Scanning immunoelectron microscopy showed that DbpA was surface accessible on intact borreliae. Passive administration of DbpA antiserum protected mice from infection following challenge with heterologous B. burgdorferi sensu stricto isolates, even when serum administration was delayed for up to 4 days after challenge. DbpA is the first antigen target identified that is capable of mediating immune resolution of early, localized B. burgdorferi infections. DbpA immunization also protected mice from B. burgdorferi challenge; DbpB immunization was much less effective. DbpA antiserum inhibited in vitro growth of many B. burgdorferi sensu lato isolates of diverse geographic, phylogenetic, and clinical origins. In combination, these findings support a role for DbpA in the immunoprophylaxis of Lyme disease and suggest that DbpA vaccines have the potential to eliminate early-stage B. burgdorferi infections.
Pheasants, Phasianus colchicus L., constitute a major part of the ground-feeding avifauna of England and Wales and are important hosts to immature stages of Ixodes ricinus L., the principal tick vector of Lyme borreliosis spirochetes in Europe. Therefore, their competence as hosts for Borrelia burgdorferi Johnson, Schmid, Steigerwalt & Brenner sensu lato was investigated. One group of pheasants was inoculated by needle with 1 x 10(6) cultured B. burgdorferi s.s. organisms, and a 2nd group of birds was infested with I. ricinus nymphs collected from a focus of Lyme borreliosis in southern England. Both bird groups were subjected to xenodiagnoses using uninfected I. ricinus nymphs. All recovered engorged ticks, as well as pheasant skin biopsies, were analyzed by a nested polymerase chain reaction targeting the 5S-23S rRNA genes of B. burgdorferi s.l. Both groups proved to be infective for ticks. The birds that were infected by tick bites proved to be significantly more infective for ticks (23% of the xenodiagnostic ticks positive) than those infected by needle (5%). The results show that pheasants can be infected experimentally with B. burgdorferi s.l., that they can pass the spirochetes to ticks and that their infectivity for ticks may persist as long as 3 mo. We conclude that pheasants are reservoir competent for Lyme borreliosis spirochetes and potentially play an important role in the maintenance of B. burgdorferi s.l. in England and Wales.
Borrelia burgdorferi sensu lato spirochetes have been found in all examined Ixodes ricinus (L.) populations in Europe. The overall mean proportions of unfed I. ricinus infected with B. burgdorferi s.l. were 1.9% (range 0-11%), 10.8% (2-43%) and 17.4% (3-58%) for larvae (n = 5699), nymphs (n = 48,804) and adults (n = 41,666), respectively. However, the results varied according to the method used. Cultivation in BSK medium is the least sensitive technique (an average of 11% adult ticks found infected), whereas polymerase chain reaction detecting spirochetal DNA is probably the most sensitive method (29% adults found infected). Microscopic methods (dark field, phase contrast, direct or indirect fluorescence) are generally comparable to each other (17-20% adults found infected) and should be regarded as standard procedures because they also make possible a quantitative estimation of spirochetes in the vector. Some technical problems of these methods are discussed.
Reported cases of Lyme disease in Hunterdon County, New Jersey, increased almost 200% from 75 (67/100,000 population) in 1992
to 216 (193/100,000 population) in 1993. For evaluation of risk factors for Lyme disease and for determination of the cause
of this increase, a case-control study was conducted, and the reporting practices of physicians' offices were evaluated. For
cases reported in 1993, age and sex distribution, month of disease onset, and proportion of cases with erythema migrans rash
were within expected limits. Analysis of age-matched case-control data showed that rural residence; clearing periresi-dential
brush during spring and summer months; and the presence of rock walls, woods, deer, or a bird feeder on residential property
were associated with incident Lyme disease. A review of physician reporting patterns suggested that the increase in reported
cases in 1993 was due to improved reporting as well as to an increase in the numbers of patients diagnosed with Lyme disease.
In addition, substantial underreporting of Lyme disease by physicians' offices was found. Am J Epidemiol 1998; 147: 391–7.
Isolated outer membranes of Borrelia burgdorferi were used in immunoblotting experiments with sera from immune mice to identify new putative Lyme disease vaccine candidates. One immunoreactive polypeptide migrated on polyacrylamide gels just proximal to outer surface protein C and comigrated with [3H]palmitate-labeled polypeptides. A degenerate oligonucleotide primer based upon internal amino acid sequence information was used to detect the corresponding gene within a B. burgdorferi total genomic library. The relevant open reading frame (ORF) encoded a polypeptide comprised of a 24-amino-acid putative signal peptide terminated by LLISC, a probable consensus sequence for lipoprotein modification, and a mature protein of 163 amino acids. Immunoblots of a recombinant fusion protein corresponding to this ORF supported the idea that the encoded protein was a previously reported decorin-binding protein (DBP) of B. burgdorferi N40 (B. P. Guo, S. J. Norris, L. C. Rosenberg, and M. Höök, Infect. Immun. 63:3467–3472, 1995). However, further DNA sequencing revealed the presence of a second ORF, designated ORF-1, whose termination codon was 119 bp upstream of the dbp gene. ORF-1 also encoded a putative lipoprotein with a mature length of 167 amino acids. Northern blots, Southern blots, and primer extension analyses indicated that ORF-1 and dbp comprised a two-gene operon located on the 49-kb linear plasmid. Both proteins, which were 40% identical and 56% similar, partitioned into Triton X-114 detergent extracts of B. burgdorferi isolated outer membranes. Mice infected with B. burgdorferi produced high titers of antibodies against the ORF-1-encoded protein and DBP during both early and later stages of chronic infection. Both DBP and the ORF-1-encoded protein were sensitive to proteinase K treatment of intact borreliae, suggesting that they were surface exposed. In active immunization experiments, 78% of mice immunized with recombinant DBP were immune to challenge. While it is not clear whether the two lipoproteins encoded by the ORF-1-dbp operon have analogous decorin-binding functions in vivo, the combined studies implicate DBP as a new candidate for a human Lyme disease vaccine.
Borrelia burgdorferi, the spirochetal agent of Lyme disease, is transmitted by Ixodes ticks. When an infected nymphal tick feeds on a host, the bacteria increase in number within the tick, after which they invade the tick’s salivary glands and infect the host. Antibodies directed against outer surface protein A (OspA) of B. burgdorferi kill spirochetes within feeding ticks and block transmission to the host. In the studies presented here, passive antibody transfer experiments were carried out to determine the OspA antibody titer required to block transmission to the rodent host. OspA antibody levels were determined by using a competitive enzyme-linked immunosorbent assay that measured antibody binding to a protective epitope defined by monoclonal antibody C3.78. The C3.78 OspA antibody titer (>213 μg/ml) required to eradicate spirochetes from feeding ticks was considerably higher than the titer (>6 μg/ml) required to block transmission to the host. Although spirochetes were not eradicated from ticks at lower antibody levels, the antibodies reduced the number of spirochetes within the feeding ticks and interfered with the ability of spirochetes to induce ospC and invade the salivary glands of the vector. OspA antibodies may directly interfere with the ability of B. burgdorferi to invade the salivary glands of the vector; alternately, OspA antibodies may lower the density of spirochetes within feeding ticks below a critical threshold required for initiating events linked to transmission.
We have sequenced the 16S rRNA molecules from four species of Borrelia and from six isolates of Borrelia burgdorferi via the reverse transcriptase primer extension method. The sequences were aligned and evolutionary relationships were determined, including the calculation of evolutionary distances and the construction of a phylogenetic tree. These analyses demonstrate significant divergence among B. burgdorferi isolates, with the European isolates G1 and G2 residing most distant from the main cluster. Signature nucleotides which distinguish B. burgdorferi from all other members of this genus and which distinguish the European isolates G1 and G2 from the North American isolates B31, Sh-2-82, and 1352 were identified. Finally, Southern blot analyses were performed to compare the restriction patterns of the genes coding for rRNA and to relate our data to the grouping scheme of Postic et al. (D. Postic, C. Edlinger, C. Richaud, F. Grimont, J. Dufresne, P. Perolat, G. Baranton, and P. A. D. Grimont, Res. Microbiol. 141:465-475, 1990).
Borrelia burgdorferi, the causative agent of Lyme disease, loses its ability to infect and cause disease in mammalian hosts after repeated in vitro passage. To identify proteins preferentially expressed by the low-passage strain and thus representing potential virulence factors, the polypeptide profiles of virulent, low-passage and nonvirulent, high-passage forms of B. burgdorferi B31 were compared by nonequilibrium pH gradient two-dimensional gel electrophoresis. Four low-passage-associated proteins with relative molecular masses (M(r)s) of 35,000, 28,000, 24,000, and 20,000 were identified. Of these, the 28- and 35-kDa polypeptides were not expressed in detectable quantities in the high-passage B31 strain, whereas the 24- and 20-kDa proteins were present in reduced quantities. All four of these proteins were lipoproteins, as determined by labelling with [3H]palmitate. The abundant 28-kDa component, called outer surface protein D (OspD), is surface exposed on the basis of its proteolysis during treatment of intact organisms with proteinase K. The ospD gene is located on a 38-kb linear plasmid present in seven of nine low-passage strains of B. burgdorferi examined but absent in most high-passage, nonvirulent strains tested. Molecular cloning and sequence analysis of the ospD gene locus revealed an open reading frame encoding a 28,436-Da polypeptide with a putative signal peptidase II leader sequence. An unusual feature of the region upstream of the gene was the presence of seven contiguous, direct repeats of a 17-bp sequence that includes consensus -35 and -10 transcription initiation signals; however, only one transcription initiation site was active as determined by primer extension analysis. Further study of these and other polypeptides associated with low-passage strains may lead to identification of B. burgdorferi gene products required for infection and pathogenesis in mammalian hosts.
To determine whether the roe deer, Capreolus capreolus L. may serve as a reservoir host for the Lyme disease spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, evidence of spirochetal infection was sought in nymphal Ixodes ricinus (L.) that had engorged as larvae on roe deer. Sixteen roe deer were shot in Lyme disease enzootic areas of south-central Sweden during August-November 1990 and August 1991. An average of 276 (range, 84-658) larvae of I. ricinus was collected from each of 12 deer shot in August. Of those ticks that had fed on deer and then developed to the nymphal stage, the gut contents of 238 were examined by phase-contrast microscopy. All these ticks were negative for spirochetes, whereas 4.2% contained Trypanosoma cf. cervi Kingston & Morton and 15.1% contained the nematode Dipetalonema rugosicauda Meszaros & Sugar. A total of 396 nymphal ticks was collected by blanket-dragging during May-June 1991 and examined for spirochetes; 9.1% of these host-seeking nymphs were infected with spirochetes. Although the roe deer serves as a principal blood source for all stages of I. ricinus, it does not appear to serve as a major reservoir of B. burgdorferi.
The discovery in 1981 of the spirochete, now known as Borrelia burgdorferi, as the etiological agent of Lyme disease in the United States and of associated clinical manifestations in Europe (11, 12) has rekindled interest in arthropod-borne spirochetoses. Since then, hundreds of publications have appeared that deal not only with the complex clinical aspects of Lyme disease but also with the natural history of this agent, and particularly its relationship to its arthropod vector—sticks of the genus Ixodes. In the United States, where Lyme disease is now considered the most prevalent tick-borne disease (16), B. burgdorferi is associated with at least three Ixodes species, namely Ixodes dammini in the northeastern and midwestern regions of the country, Ixodes pacificus in the West, and possibly Ixodes scapularis in the Southeast. In Europe (55), the sheep or castor bean tick, Ixodes ricinus, is the vector, whereas in Asia Ixodes persulcatus is said (17) to be involved in the maintenance and distribution of the Lyme disease spirochete.
When two comparable herds of cattle were kept continuously in adjoining paddocks, frequent acaricidal treatment was necessary to control ticks (Boophilus microplus (Canestrini) ). Thereafter, one of the two herds was grazed alternately in its own and an adjacent paddock, the intervals between each transfer being sufficient to ensure that most of the ticks in the unoccupied paddock had died. Tick infestations on this herd were greatly reduced, and less frequent use of acaricides was necessary. The herd remaining in the continuously stocked pasture continued to need acaricidal treatment for recurring tick infestation. In a field trial with 350–400 cattle moved a t intervals to each of three formerly heavily infested paddocks, tick infestations remained very light, although the herd was dipped only In January, September, and the following January. A control herd on continuously stocked pasture, treated at the owner's discretion, required eight dippings in this period. This procedure of "pasture spelling" seems likely to be widely applicable in central Queensland.
A review of reports on the genetic and phenotypic characteristics of strains of the spirochete which causes Lyme disease revealed that these organisms are representative of a new species of Borrelia. We propose the name Borrelia burgdorferi for this species. The type strain of B. burgdorferi is strain B31 (= ATCC 35210). In two separate studies the guanine-plus-cytosine content of the deoxyribonucleic acid of the type strain was determined to be 29.0 to 30.5 mol% (thermal denaturation method).
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Thiobacillus versutus was shown to harbour pTAV2 plasmid with certain characteristics atypical for cccDNA. Preliminary evidence is presented that the plasmid may have the structure of a double-stranded linear DNA molecule.
To the Editor:
—The following quotation is from an editorial on Rocky Mountain spotted fever, which appeared in The Journal
To determine whether the abundance of the northern deer tick, Ixodes dammini is dependent upon that of white-tailed deer, Odocoileus virginianus (Boddaert), the host most frequently parasitized by adult ticks, we compared the relative abundance of deer and of immature ticks on 13 islands in Massachusetts. Abundance of larval I. dammini attached to white-footed mice, Peromyscus leucopus (Raphinesque), correlated with density of deer pellet groups, and was greatest on islands having resident deer and least on islands with few signs of deer. This relationship did not hold in the case of nymphal ticks. Deer density may largely determine abundance of larvae by affecting success of adult engorgement and subsequent reproduction. The more diffuse distribution of nymphal ticks may, in part, be explained by the tendency of larval (but not adult) ticks to be transported between islands while feeding on birds.
In tests conducted at Baton Rouge and Pine Grove, Louisiana, various stages of the lone star tick, Amblyomma americanum (L.), were released in areas infested with the imported fire ant, Solenopsis saevissima richteri Forel, and in areas where mirex bait was applied to suppress ant populations. A significant (P<0.01) greater survival of tick eggs and engorged tick larvae occurred in the mirex-treatcd area after 24, 48, and 72 hours of exposure to fire ant predation. About 75% of the ticks released in the mirextreated plot in August and September 1970 as nymphs were recovered as adults in March 1971. No ticks were recovered in the ant-infested plot.
Engorged female ticks confined in hardware-cloth cages had a much higher survival rate in the mirex-treated plots.
Ticks were collected at the eastern tip of Long Island from May through October 1971 on 11 mammal and 8 bird host species and by dragging. A total of 3845 ticks of 6 species were taken. Tabulations showing host relations and seasonal distribution are given. Amblyomma americanum (L.) was found to be established in one area. Norway rats appeared to be favorite hosts for larvae and nymphs of Dermacentor variabilis (Say). Heavy infestations of Ixodes muris Bishopp & Smith were found on white-footed mice and on a muskrat. This species also was found on 8 species of birds, including lst-time records on 5 bird species. Adults of Ixodes scapularis Say were prevalent in October and it is concluded that this is a fall-spring species.
During the last few decades, a considerable amount of experimental works has been carried out on the relations of insects to their environment: in certain groups such studies have advanced to an extent which renders possible tentative efforts at accurate prediction of their activities and spread. Among the arachnids, however, the experimental study of ecological relationships has been almost entirely neglected, and this despite the fact that several species, especially among the mites and ticks, are of marked economic significance. Since 1892–3, when the researches of Smith and Kilborne on piroplasmosis in cattle were published, ticks have been proved to be vectors of numerous important diseases of man and animals in many parts of the world, and much knowledge of their bionomics has been gained through observations conducted in the field and in the laboratory. The ecology of ticks under precisely controlled conditions, however, provides a practically unexplored field.(Received November 08 1933)
In the absence of published data application was made to various authorities for their opinions and for any detailed information they might have. Astonishingly diverse replies were given. The head of a veterinary laboratory in one of the East African dependencies wrote as follows : “ I believe they do pick off ticks, although I doubt if they eat these ; their object being to find a wound. When they have succeeded they feed on the exposed raw tissue.” Another local veterinary authority remarked : “ They cause a great deal of damage through the sores they produce in stock.” A gamewarden said : “ I always regarded the oxpecker as an unmitigated nuisance and pest. The prevalent idea that this bird frees domestic stock of ticks appears to be entirely erroneous.… These birds feed mainly on the raw tissue of open wounds and it is by their action that the open wounds usually occur.” Other observers of wide experience are less downright.
Selected aspects of ecological interactions with ticks, tick-borne diseases and their hosts are discussed in relation to Integrated Tick Management, The needs to preserve tick-borne disease enzootic stability and to ensure the economic justification for any interventions were emphasized.RésuméAspects séléctés des intéractions écologiques avec les tiques, les maladies transmitté par les tiques et leurs hôtes sont discutés en relation au Management Integré des Tiques. Les bésoins de préserver la stabilité enzootique des maladies transmitté par les tiques et pour ensurer la justification économique pour tous les interventions ont emphasisé.
Spirochetes were found in 13% of Ixodes ricinus collected from an island, near Stockholm where human borreliosis is endemic. Borrelia burgdorferi was cultivated from the kidney and/or spleen of wild rodents (Clethrionomys glareolus and Apodemus flavicollis) from the same island. Spirochetes were identified as Borrelia burgdorferi by indirect immunofluorescence assays using species and genus specific monoclonal antibodies. In these tests the spirochetes could not be differentiated from strains previously cultured from Swedish patients with Ixodes-borne borreliosis. The results show that small rodents in Europe may harbour borreliae and indicate that C. glareolus and A. flavicollis may be important reservoirs for the spirochetes causing Ixodes-borne borreliosis in humans and domestic animals in Europe.