"Moreover, the incidence of tickborne diseases is increasing worldwide ( Jongejan and Uilenberg 2004, Nicholson et al. 2010, Piesman et al. 2012). For example, more than 250,000 human cases of Lyme borreliosis were reported from 2000 to 2010 in the United States, and the disease also is increasing in Europe, where over 50,000 human cases are reported annually (Piesman et al. 2012). The spectrum of tick-borne diseases affecting domestic animals and humans also has increased in recent years with the emergence of many important zoonotic tickborne illnesses, such as anaplasmosis, babesiosis, ehrlichiosis , and members of the tick-borne encephalitis serocomplex including Powassan virus (POWV; Flaviridae, Flavivirus) (de la Fuente et al. 2012). "
[Show abstract][Hide abstract] ABSTRACT: Abstract Ixodes scapularis, the blacklegged tick, is capable of transmitting the pathogens that cause Lyme disease (Borrelia burgdorferi), babesiosis (Babesia microti), anaplasmosis (Anaplasma phagocytophilum), and to a lesser extent Powassan encephalitis (deer tick virus [DTV]). These pathogens represent significant public health problems, but little is known about the occurrence and co-infection prevalence of these pathogens in I. scapularis. Here, we used standard PCR and pathogen-specific primers to estimate the prevalence of infection of A. phagocytophilium, B. burgdorferi, B. microti, and Ehrlichia chaffeensis in questing nymph and adult I. scapularis collected from sites in Putnam and Dutchess counties in southern New York in 2011. To detect DTV infection, cell cultures were observed for the presence of cytopathic effects and positive results were confirmed via real time RT-PCR. In 466 individually sampled adult ticks, B. burgdorferi had the highest prevalence of infection (55%) followed by A. phagocytophilum (18.2%), DTV (3.4%), B. microti (3.2%), and E. chaffeensis (1.5%). Infection with two pathogens occurred in 13.3% of ticks, and 10 ticks were infected with three combinations of three pathogens. These results provide an estimate of the rate of co-infection, which then can help inform the epidemiological risk of contracting multiple zoonotic tick-borne pathogens within the Hudson Valley region of New York State.
"Other control approaches deal directly with the vertebrate host system. These include lowering the transmission rate through antibiotic treatment of vertebrate host species (Dolan et al., 2011), vaccination of the main vertebrate host (Tsao et al., 2004, 2012) and the use of acaracide to control ticks by application to vertebrate hosts or area wide spraying (Piesman and Beard, 2012). We performed global sensitivity analyses to identify the parameters of the model that explain most of the variation in R 0 over the parameter space defined by the parameter ranges. "
[Show abstract][Hide abstract] ABSTRACT: The basic reproduction number of a pathogen, R0, determines whether a pathogen will spread (R0>1), when introduced into a fully susceptible population or fade out (R0<1), because infected hosts do not, on average, replace themselves. In this paper we develop a simple mechanistic model for the basic reproduction number for a group of tick-borne pathogens that wholly, or almost wholly, depend on horizontal transmission to and from vertebrate hosts. This group includes the causative agent of Lyme disease, Borrelia burgdorferi, and the causative agent of human babesiosis, Babesia microti, for which transmission between co-feeding ticks and vertical transmission from adult female ticks are both negligible. The model has only 19 parameters, all of which have a clear biological interpretation and can be estimated from laboratory or field data. The model takes into account the transmission efficiency from the vertebrate host as a function of the days since infection, in part because of the potential for this dynamic to interact with tick phenology, which is also included in the model. This sets the model apart from previous, similar models for R0 for tick-borne pathogens. We then define parameter ranges for the 19 parameters using estimates from the literature, as well as laboratory and field data, and perform a global sensitivity analysis of the model. This enables us to rank the importance of the parameters in terms of their contribution to the observed variation in R0. We conclude that the transmission efficiency from the vertebrate host to Ixodes scapularis ticks, the survival rate of Ixodes scapularis from fed larva to feeding nymph, and the fraction of nymphs finding a competent host, are the most influential factors for R0. This contrasts with other vector borne pathogens where it is usually the abundance of the vector or host, or the vector-to-host ratio, that determine conditions for emergence. These results are a step towards a better understanding of the geographical expansion of currently emerging horizontally-transmitted tick-borne pathogens such as Babesia microti, as well as providing a firmer scientific basis for targeted use of acaricide or the application of wildlife vaccines that are currently in development.
"For Lyme disease, timecourse studies revealed that transmission of Borrelia burgdorferi does not occur until the second day of attachment by Ixodes scapularis Say nymphs (the life stage associated with most human cases) and then the probability of transmission increases with time attached (Piesman et al. 1987, Piesman 1993, des Vignes et al. 2001, Hojgaard et al. 2008). Thus, in addition to recommending avoidance of tick bites (e.g., use of personal protection against ticks, tick reduction by landscape modiÞcation or use of acaricides, avoiding risk areas during periods of host-seeking activity) frequent tick checks and prompt tick removal are frequently recommended for the prevention of Lyme disease (Piesman and Eisen 2008). Although most of these recommendations are transferable to tularemia prevention, our results show that transmission can occur shortly after attachment; thus, prompt removal of D. variablis adults may reduce but not eliminate the chance of F. tularensis transmission. "
[Show abstract][Hide abstract] ABSTRACT: The American dog tick, Dermacentor variabilis (Say) (Acari: Ixodidae), has been implicated as a potential bridging vector to humans of Francisella tularensis, the etiological agent of tularemia. Since the initial studies evaluating vector competency of D. variabilis were conducted, F. tularensis has been subdivided into subspecies and clades that differ in their geographical distribution in the United States and in the severity of infections caused in humans. Here, we demonstrate that D. variabilis nymphs efficiently acquire, transtadially maintain, and transmit each of the strains tested (clades A1b and A2, and type B). Transmission efficiency by adult females was similarly high among infection groups and ranged from 58% for type B to 89% for A2 infections. In addition, we demonstrated that transmission can occur shortly after tick attachment. These findings support the concept that D. variabilis adults may play a significant role in epizootic transmission of F. tularensis, and as a bridging vector to humans.
Journal of Medical Entomology 07/2011; 48(4):884-90. DOI:10.1603/ME11005 · 1.82 Impact Factor
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