Article

Trypanosoma cruzi-Trypanosoma rangeli co-infection ameliorates negative effects of single trypanosome infections in experimentally infected Rhodnius prolixus

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Abstract

Trypanosoma cruzi, causative agent of Chagas disease, co-infects its triatomine vector with its sister species Trypanosoma rangeli, which shares 60% of its antigens with T. cruzi. Additionally, T. rangeli has been observed to be pathogenic in some of its vector species. Although T. cruzi-T. rangeli co-infections are common, their effect on the vector has rarely been investigated. Therefore, we measured the fitness (survival and reproduction) of triatomine species Rhodnius prolixus infected with just T. cruzi, just T. rangeli, or both T. cruzi and T. rangeli. We found that survival (as estimated by survival probability and hazard ratios) was significantly different between treatments, with the T. cruzi treatment group having lower survival than the co-infected treatment. Reproduction and total fitness estimates in the T. cruzi and T. rangeli treatments were significantly lower than in the co-infected and control groups. The T. cruzi and T. rangeli treatment group fitness estimates were not significantly different from each other. Additionally, co-infected insects appeared to tolerate higher doses of parasites than insects with single-species infections. Our results suggest that T. cruzi-T. rangeli co-infection could ameliorate negative effects of single infections of either parasite on R. prolixus and potentially help it to tolerate higher parasite doses.

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... rangeli) on Chagas disease is secondary: T. rangeli shares with T. cruzi the large overlaps of geographical distribution, and the same mammalian hosts and triatomine species, particularly for example Rhodnius prolixus (R. prolixus) [39]. Despite being considered nonpathogenic to mammal hosts, T. rangeli is epidemiologically important for Chagas disease transmission since it may cause false-positive diagnosis of Chagas disease, and it is pathogenic to triatomine vectors, leading to the reduction of vector reproduction and survival [15,19,35]. This can alter the triatomine bugs population dynamics and subsequently alter the Chagas disease spreading process. ...
... Due to the great epidemiological importance of T. cruzi and T. rangeli, and their co-infection is an important component for predicting and preventing Chagas disease transmission risk. Indeed, there are some biological evidences that prevalence of these two parasites co-infection at natural contiguous forests and domestic/peridomestic habitats is common for both vertebrate hosts and invertebrate traitomine bugs, particularly genus Rhodnius which are key vectors for propagating Chagas disease to humans [14,17,18,20,35,48]. Moreover, biological studies of the effects of T. cruzi and T. rangeli co-infection on the fitness of triatomines R. prolixus and mammals are often reported [3,4,5,6,35]. ...
... Indeed, there are some biological evidences that prevalence of these two parasites co-infection at natural contiguous forests and domestic/peridomestic habitats is common for both vertebrate hosts and invertebrate traitomine bugs, particularly genus Rhodnius which are key vectors for propagating Chagas disease to humans [14,17,18,20,35,48]. Moreover, biological studies of the effects of T. cruzi and T. rangeli co-infection on the fitness of triatomines R. prolixus and mammals are often reported [3,4,5,6,35]. Whereas, how to mathematically model this T. cruzi and T. rangeli co-infection and T. rangeli-induced pathogenicity of triatomine bugs and to evaluate their effects in the spread of Chagas disease have not been investigated to our best knowledge. ...
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A mathematical model is developed to investigate the impact of Trypanosoma cruzi and Trypanosoma rangeli co-infection and Trypanosoma rangeli-induced pathogenicity of triatomine bugs on the spread of Chagas disease. Due to the presence of two parasites, basic reproduction numbers of one parasite in the absence of the other parasite (\begin{document}$ \mathcal{R}_{10} $\end{document} and \begin{document}$ \mathcal{R}_{20} $\end{document}) and invasion reproduction numbers of one parasite invading the other parasite (\begin{document}$ \mathcal{R}_{12} $\end{document} and \begin{document}$ \mathcal{R}_{21} $\end{document}) are derived to determine the dynamics of the co-infection system. With a simple case of two parasites' independent transmission, we have found that both parasites go extinct if both \begin{document}$ \mathcal{R}_{i0}<1\,(i=1,2) $\end{document}, thus no Chagas disease spread. Nevertheless, the condition of \begin{document}$ \mathcal{R}_{i0}>1\,(i=1,2) $\end{document} is not sufficient to cause Chagas disease persistence, the invasion reproduction number of Trypanosoma cruzi invading Trypanosoma rangeli transmission \begin{document}$ \mathcal{R}_{12} $\end{document} plays an important role. Specifically, Chagas disease could go extinct if \begin{document}$ \mathcal{R}_{12}<1 $\end{document}, and uniformly persistent if \begin{document}$ \mathcal{R}_{12}>1 $\end{document}. Moreover, due to pathogenicity, oscillation pattern of Chagas disease is observed, which is different from other mechanisms such as maturation delay, seasonality and regular spraying with insecticides for vector control. In conclusion, we have found that the presence of Trypanosoma rangeli infection leads to the risk reduction of Chagas disease infection. Our findings are beneficial to the prevention and control of Chagas disease.
... Trypanosoma cruzi infection reduces bug survival (e.g. Peterson et al., 2016;Cordero-Montoya et al., 2019; reviewed by de Oliveira et al., 2018). This cost could lead the insect to enhance its immune response (de Fuentes-Vicente et al., 2016), removing up to 80% of the parasites within hours after ingesting infected blood (Elliot et al., 2015;Hinestroza et al., 2016). ...
... The authors of that study suggested the existence of a protective effect by T. cruzi against fungal infections. Interestingly, multiple infections by T. cruzi and T. rangeli resulted in higher survival rates than single T. cruzi infections (Peterson et al., 2016), supporting the hypothesis of a protective effect by T. cruzi against possible competitors. The authors suggested that the microbiota interacting with T. cruzi in the triatomine gut could mediate this protective effect by releasing antimicrobial compounds against the fungus (Garcia et al., 2016). ...
Article
Triatomine bugs carry the parasitic protozoa Trypanosoma cruzi , the causal agent of Chagas disease. It is known that both the parasite and entomopathogenic fungi can decrease bug survival, but the combined effect of both pathogens is not known, which is relevant for biological control purposes. Herein, the survival of the triatomine Meccus pallidipennis (Stal, 1872) was compared when it was coinfected with the fungus Metarhizium anisopliae (Metschnikoff) and T. cruzi , and when both pathogens acted separately. The immune response of the insect was also studied, using phenoloxidase activity in the bug gut and hemolymph, to understand our survival results. Contrary to expectations, triatomine survival was higher in multiple than in single challenges, even though the immune response was lower in cases of multiple infection. We postulate that T. cruzi exerts a protective effect and/or that the insect reduced the resources allocated to defend itself against both pathogens. Based on the present results, the use of M. anisopliae as a control agent should be re-considered.
... The evolutionary dynamics between triatomines and trypanosome parasites indicate a possible arms race and manipulation by the parasite as suggested for vector borne diseases (Lefevre and Thomas, 2008). While the infection causes a reduction in several aspects of the bug's fitness (development: Botto-Mahan, 2009;Cordero-Montoya et al., 2019;fecundity: Fellet et al., 2014;Cordero-Montoya et al., 2019;and survival: Elliot et al., 2015;Hinestroza et al., 2016;Peterson et al., 2016;Cordero-Montoya et al., 2019), the bug also reduces the survival of the parasite (Ferreira et al., 2016; however, for no effects see Schaub, 1988Schaub, , 1989. In addition, different T. cruzi isolates vary in their negative effects on bug fitness (Cordero-Montoya et al., 2019), and infection limits the bugs' niche exploitation potential (Villalobos et al., 2019). ...
... In fact, the results of fitness effects in other species of bugs also show different effects. For example, while different studies have found negative effects of T. cruzi infection on different aspects of the bugs' life history (development, Botto-Mahan, 2009;reproduction, Fellet et al., 2014;survival, Elliot et al., 2015;Peterson et al., 2016), other studies have not found these effects (Zeledón et al., 1970;Schaub, 1988;Elliot et al., 2015). ...
... There are ideas that suggest a coevolutionary scenario based on the costs to the triatomine in terms of development (Botto-Mahan et al. 2006), reproduction (e.g. fecundity, Fellet et al. 2014), and survival (Elliot et al. 2015;Hinestroza et al. 2016;Peterson et al. 2016). However, these studies have not simultaneously evaluated the effects of carrying the parasite on all three of these life history traits (development, reproduction, and survival), which does not allow the recognition of possible trade-offs in the bug. ...
... These general results do not differ from other studies carried out in other species of triatomines. For example, negative effects of infection have been detected in terms of development (Botto-Mahan et al. 2006), fecundity (Fellet et al. 2014), and survival (Elliot et al. 2015;Hinestroza et al. 2016;Peterson et al. 2016), though there are also studies that have not found these effects (e.g. Zeledón et al. 1970;Schaub 1988;Elliot et al. 2015). ...
Article
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Relatively little is known about the fitness effects and life history trade-offs in medically important parasites and their insect vectors. One such case is the triatomine bugs and the parasite Trypanosoma cruzi, the key actors in Chagas disease. Previous studies have revealed some costs but have not simultaneously examined traits related to development, reproduction, and survival or their possible trade-offs. In addition, these studies have not compared the effects of genetically different T. cruzi strains that differ in their weakening effects in their vertebrate hosts. We compared the body size of the bugs after infection, the number of eggs laid, hatching/non-hatching rate, hatching success, survival, and the resulting number of parasites in Meccus (Triatoma) pallidipennis bugs that were experimentally infected with two strains of T. cruzi (Chilpancingo [CH], the most debilitating in vertebrates; and Morelos [MO], the least debilitating) (both belonging to TcI group). Our results showed that infection affects size (MO < CH; MO and CH = control), number of eggs laid (MO and CH < control) hatching/non-hatching rate (MO < control < CH), hatching success (control < MO, CH = control = MO), and survival (Chilpancingo < Morelos < control). In addition, the CH strain produced more parasites than the MO strain. These results suggest that (a) infection costs depend on the parasite’s origin, (b) the more debilitating effects of the CH strain are due to its increased proliferation in the host, and (c) differences in pathogenicity among T. cruzi strains can be maintained through their different effects on hosts’ life history traits. Probably, the vectorial capacity mediated by a more aggressive strain could be reduced due to its costs on the triatomine, leading to a lower risk of vertebrate and invertebrate infection in natural populations.
... While several works have analyzed the mechanisms associated with T. cruzi-vector dynamics (e.g., biotic and abiotic factors) to understand the T. cruzi-triatomine interactions, under a co-evolutionary scenario [54], literature about how the parasites may influence the insects is more limited, and the studies have mainly been focused on the parasite's effects on four patterns of the vector behavior: life-history traits, feeding, defecation, and dispersion/ locomotion [55]. Different studies have found negative effects of T. cruzi infection on vector survival [56][57][58][59], fecundity [59,60], post-embryonic development [59,61,62], behavior [55,[63][64][65][66][67][68], and physiological processes [55,60,[69][70][71], while other studies have not identified these effects on patterns of alimentation/defecation [56,72,73], development, and reproduction [74][75][76]. Overall, most of these studies determined that the effects of T. cruzi are species-dependent, age-dependent, sex-dependent, and even environment/physiology-dependent. ...
Article
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Background Triatoma dimidiata is a vector of the protozoan parasite Trypanosoma cruzi , the etiologic agent of Chagas disease. Phenotypic plasticity allows an organism to adjust its phenotype in response to stimuli or environmental conditions. Understanding the effect of T. cruzi on the phenotypic plasticity of its vectors, known as triatomines, has attracted great interest because of the implications of the parasite–triatomine interactions in the eco-epidemiology and transmission of the etiologic agent of Chagas disease. We investigated if the infection of the vector with T. cruzi may be associated with a change in the antennal phenotype of sylvatic, domestic, and laboratory-reared populations of T. dimidiata . Methods The abundance of each type of sensillum (bristles, basiconic, thick- and thin-walled trichoid) on the antennae of T. cruzi -infected and non-infected T. dimidiata reared in the laboratory or collected in sylvatic and domestic ecotopes were measured under light microscopy and compared using Kruskal–Wallis non-parametric tests and permutational multivariate analysis of variance. Results We found significant differences between sensilla patterns of infected and non-infected insects within sylvatic and domestic populations. Conversely, we found no significant differences between sensilla patterns of infected and non-infected insects within the laboratory-reared population. Besides, for sylvatic and domestic populations, sexual dimorphism tended to be increased in infected insects. Conclusion The differences observed in infected insects could be linked to higher efficiency in the perception of odor molecules related to the search for distant mates and hosts and the flight dispersal in search of new habitats. In addition, these insects could have a positive effect on population dynamics and the transmission of T. cruzi . Graphical Abstract
... Rhodnius montenegrensis has also been reported in domestic environments, but only in the countryside 18 . In addition, it has been found to be naturally infected with Trypanosoma rangeli Tejera, 1920, which is of major importance because the difficulty in isolation and diagnosis may be related to a double trypanosomatid infection, which can lead to false positive or true positive results for Chagas disease 18,19 . This new report on the occurrence of R. montenegrensis expands the geographic distribution of the species in Latin America, with Bolivia being the second country to register the presence of the insect and increasing the number of species described in the locality. ...
Article
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Background: The subfamily Triatominae, which comprises 157 species, carries the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease. This short communication reports for the first time the occurrence of Rhodnius montenegrensis in Bolivia. Methods: Active searches were carried out on palm trees of the genus Oenocarpus in Beni district, Bolivia. Results: Fifteen R. montenegrensis specimens were collected from a rural area of the Beni district, Bolivia, and tested positive for T. cruzi. Conclusions: This new report expands the geographic distribution of the species in Latin America. Due to their ability to transmit trypanosomatids, the species deserves the attention of vector control programs.
... Unlike mammals, the parasite is pathogenic to triatomine species of the genus Rhodnius [8,11,12]. Trypanosoma rangeli and T. cruzi usually share mammalian hosts, and their distributions in nature often overlap in simple or mixed infections in mammals and triatomines [4,[13][14][15][16]. ...
Article
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Trypanosoma rangeli is a generalist hemoflagellate that infects mammals and is transmitted by triatomines around Latin America. Due to its high genetic diversity, it can be classified into two to five lineages. In Brazil, its distribution outside the Amazon region is virtually unknown, and knowledge on the ecology of its lineages and on host species diversity requires further investigation. Here, we analyzed 57 T. rangeli samples obtained from hemocultures and blood clots of 1392 mammals captured in different Brazilian biomes. The samples were subjected to small subunit (SSU) rDNA amplification and sequencing to confirm T. rangeli infection. Phylogenetic inferences and haplotype networks were reconstructed to classify T. rangeli lineages and to infer the genetic diversity of the samples. The results obtained in our study highlighted both the mammalian host range and distribution of T. rangeli in Brazil: infection was observed in five new species (Procyon cancrivorous, Priodontes maximum, Alouatta belzebul, Sapajus libidinosus, and Trinomys dimidiatus), and transmission was observed in the Caatinga biome. The coati (Nasua nasua) and capuchin monkey (S. libidinosus) are the key hosts of T. rangeli. We identified all four T. rangeli lineages previously reported in Brazil (A, B, D, and E) and possibly two new genotypes.
... 92 The reproduction is also reduced by one of these strains. 133 Also, in Triatoma sp. and R. prolixus, the longevity of T. cruzi-infected adults is reduced, 134,135 in the latter even more after feeding on T. cruzi-infected guinea pigs compared to groups fed on uninfected guinea pigs. After feeding on uninfected hosts, no effects of T. cruzi infection are evident on the mean lifespan of both adult males and females of T. brasiliensis and T. dimidiata, as well as the hatching rate of eggs, the period of time before oviposition, the number of ovipositions, and both the total number of eggs laid and number of fertile eggs. ...
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This review focusses on the interactions between the etiologic agent of Chagas disease, Trypanosoma cruzi, and its triatomine vector. The flagellate mainly colonizes the intestinal tract of the insect. The effect of triatomines on trypanosomes is indicated by susceptibility and refractoriness phenomena that vary according to the combination of the strains. Other effects are apparent in the different regions of the gut. In the stomach, the majority of ingested blood trypomastigotes are killed while the remaining transform to round stages. In the small intestine, these develop into epimastigotes, the main replicative stage. In the rectum, the population density is the highest and is where the infectious stage develops, the metacyclic trypomastigote. In all regions of the gut, starvation and feeding of the triatomine affect T. cruzi. In the small intestine and rectum, starvation reduces the population density and more spheromastigotes develop. In the rectum, feeding after short-term starvation induces metacyclogenesis and after long-term starvation the development of specific cells, containing several nuclei, kinetoplasts and flagella. When considering the effects of T. cruzi on triatomines, the flagellate seems to be of low pathogenicity. However, during stressful periods, which are normal in natural populations, effects occur often on the behaviour, eg, in readiness to approach the host, the period of time before defecation, dispersal and aggregation. In nymphs, the duration of the different instars and the mortality rates increase, but this seems to be induced by repeated infections or blood quality by the feeding on infected hosts. Starvation resistance is often reduced by infection. Longevity and reproduction of adults is reduced, but only after infection with some strains of T. cruzi. Only components of the surface coat of blood trypomastigotes induce an immune reaction. However, this seems to act against gut bacteria and favours the development of T. cruzi.
... Examples of pathogens promoting longer vector lifespan are sparser than behavioral changes, being reported for T. brucei gambiense-infected Glossina palpalis [35] and T. brucei rhodesienseand T. brucei-infected G. morsitans morsitans [36,37]. In contrast, pathogen infection can also lead to reduced lifespan and fecundity, as reported for Leishmania-infected sandflies [38], Cx. pipiens infected by the Rift Valley fever virus [39], and Trypanosoma-infected triatomine bugs [40][41][42], as examples of possible evolutionary arms races [27]. ...
Article
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Pathogens can manipulate the phenotypic traits of their hosts and vectors, maximizing their own fitness. Among the phenotypic traits that can be modified, manipulating vector behavior represents one of the most fascinating facets. How pathogens infection affects behavioral traits of key insect vectors has been extensively investigated. Major examples include Plasmodium, Leishmania and Trypanosoma spp. manipulating the behavior of mosquitoes, sand flies and kissing bugs, respectively. However, research on how pathogens can modify tick behavior is patchy. This review focuses on current knowledge about the behavioral changes triggered by Anaplasma, Borrelia, Babesia, Bartonella, Rickettsia and tick-borne encephalitis virus (TBEV) infection in tick vectors, analyzing their potential adaptive significance. As a general trend, being infected by Borrelia and TBEV boosts tick mobility (both questing and walking activity). Borrelia and Anaplasma infection magnifies Ixodes desiccation resistance, triggering physiological changes (Borrelia: higher fat reserves; Anaplasma: synthesis of heat shock proteins). Anaplasma infection also improves cold resistance in infected ticks through synthesis of an antifreeze glycoprotein. Being infected by Anaplasma, Borrelia and Babesia leads to increased tick survival. Borrelia, Babesia and Bartonella infection facilitates blood engorgement. In the last section, current challenges for future studies are outlined.
... Despite earlier reports suggesting T. rangeli infection is pathogenic to triatomines, more recent studies point to the need of more solid evidence before generalizing this claim [72]. Indeed, recent reports suggest co-infection increases R. prolixus survival, reproduction and fitness, which in turn would favor transmission of both parasite species [73]. The interplay of the infection with these two trypanosomatids in R. ecuadoriensis and its possible impact over the epidemiology of Chagas disease in the south of Ecuador warrants further investigation. ...
Article
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Background: Trypanosoma cruzi, the causative agent of Chagas disease, and T. rangeli are kinetoplastid parasites endemic to Latin America. Although closely related to T. cruzi and capable of infecting humans, T. rangeli is non-pathogenic. Both parasite species are transmitted by triatomine bugs, and the presence of T. rangeli constitutes a confounding factor in the study of Chagas disease prevalence and transmission dynamics. Trypanosoma cruzi possesses high molecular heterogeneity: seven discrete typing units (DTUs) are currently recognized. In Ecuador, T. cruzi TcI and T. rangeli KP1(-) predominate, while other genetic lineages are seldom reported. Methods: Infection by T. cruzi and/or T. rangeli in different developmental stages of triatomine bugs from two communities of southern Ecuador was evaluated via polymerase chain reaction product size polymorphism of kinetoplast minicircle sequences and the non-transcribed spacer region of the mini-exon gene (n = 48). Forty-three mini-exon amplicons were also deep sequenced to analyze single-nucleotide polymorphisms within single and mixed infections. Mini-exon products from ten monoclonal reference strains were included as controls. Results: Trypanosoma cruzi genetic richness and diversity was not significantly greater in adult vectors than in nymphal stages III and V. In contrast, instar V individuals showed significantly higher T. rangeli richness when compared with other developmental stages. Among infected triatomines, deep sequencing revealed one T. rangeli infection (3%), 8 T. cruzi infections (23.5%) and 25 T. cruzi + T. rangeli co-infections (73.5%), suggesting that T. rangeli prevalence has been largely underestimated in the region. Furthermore, deep sequencing detected TcIV sequences in nine samples; this DTU had not previously been reported in Loja Province. Conclusions: Our data indicate that deep sequencing allows for better parasite identification/typing than amplicon size analysis alone for mixed infections containing both T. cruzi and T. rangeli, or when multiple T. cruzi DTUs are present. Additionally, our analysis showed extensive overlap among the parasite populations present in the two studied localities (c.28 km apart), suggesting active parasite dispersal over the study area. Our results highlight the value of amplicon sequencing methodologies to clarify the population dynamics of kinetoplastid parasites in endemic regions and inform control campaigns in southern Ecuador.
... In addition, Rhodnius montenegrensis Rosa et al., 2012 has also been found in houses in a rural area 13 , and its natural infection by T. rangeli, which was observed in this study, has also been confi rmed 10 . These results are worrying, since the occurrence of these parasites and the mixed infection by both T. cruzi and T. rangeli may hinder isolation and differential diagnosis, leading to possible misdiagnoses of Chagas disease 14 . All the insects collected in the study were at the adult stage and showed no domiciliation. ...
Article
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Introduction: This study describes the occurrence of triatomines, and their positivity for trypanosomatids, in a residential complex in Rio Branco, Acre, Brazil. Methods: Triatomines were collected through direct capture in a home environment. Positivity analysis for trypanosomatids was performed by PCR assays. Results: Collected insects consisted of 31 Rhodnius robustus, 4 Rhodnius montenegrensis, and 1 Panstrongylus geniculatus specimens. All were adults, with no presence of domiciliation, and with an infection rate of 30.6%. Conclusions: Future studies are recommended in other locations of Rio Branco in order to develop a georeference database of the occurrence of triatomines in urban areas.
... 36 In triatomine bugs, the known vectors of T. cruzi, some studies report that T. cruzi retards development time, reduces survival, decreases reproductive rates, and modifies other phenotypes in T. cruzi-infected bugs, [37][38][39][40] whereas others have reported no significant effects. [41][42][43] Life history variation in T. cruzi-infected triatomines has also been associated with insect age, sex, 39 T. cruzi strain, 44 parasite community within the host, 45,46 and temperature. 47 Cimex heterogeneity. ...
Article
Although not presently implicated as a vector of human pathogens, the common bed bug, Cimex lectularius, has been suspected of carrying human pathogens because of its close association with humans and its obligate hematophagy. Recently, we characterized the vectorial competence of C. lectularius for the parasite Trypanosoma cruzi, the causative agent of Chagas disease. We observed that C. lectularius can acquire T. cruzi infection when fed on T. cruzi-carrying mice, and subsequently transmit T. cruzi to uninfected mice. This led us to ask why has C. lectularius not been implicated in the transmission of T. cruzi outside of the laboratory? We hypothesized that T. cruzi reduces C. lectularius fitness (i.e., survival and/or reproduction) as an explanation for why C. lectularius does not to transmit T. cruzi in natural settings. We tested this hypothesis by comparing the survival and reproduction of uninfected and T. cruzi-infected C. lectularius. We observed that T. cruzi had a variable effect on C. lectularius survival and reproduction. There were negligible differences between treatments in juveniles. Infected adult females tended to live longer and produce more eggs. However, no effect was consistent, and infected bugs showed more variation in survival and reproduction metrics than control bugs. We did not observe any negative effects of T. cruzi infection on C. lectularius survival or reproduction, suggesting that decreased fitness in T. cruzi-infected C. lectularius is not why bed bugs have not been observed to transmit T. cruzi in natural settings.
... The occurrence of T. rangeli naturally infecting R. stali offers increased knowledge of the geographical distribution of this parasite in the northern region of Brazil, because it acts as an alert regarding epidemiological surveillance of the same area. Moreover, it is known that the occurrence of T. cruzi and T. rangeli in the same geographical region, allows for the occurrence of mixed infections in both vertebrate hosts and vectors 1 , making it diffi cult to isolate and differentially diagnose the infection, leading to misdiagnoses of Chagas disease 15 . This situation is of concern, especially in regions where other vector species of T. rangeli are reported, such as the state of Acre, where they occur in addition to R. stali, for example, the species R. pictipes, R. robustus and R. montenegrensis 10,14 . ...
Article
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Introduction: Rhodnius stali infection by Trypanosoma rangeli is reported in this study for the first time. Methods: The triatomines were collected from the campus of the Federal University of Acre in Rio Branco, Acre, Brazil. The identification of T. rangeli was confirmed by multiplex polymerase chain reaction. Results: The examinations of two specimens revealed R. stali infection by the epimastigote forms of T. rangeli. Conclusions: The encounter of R. stali infected by T. rangeli generates an alert for the state of Acre, since the simultaneous presence with Trypanosoma cruzi can make the differential diagnosis of Chagas disease difficult.
... Parasite strain was also shown to affect whether T. cruzi exert effects on the duration of triatomine molt and life-span, as some Tc1 T. cruzi strains extended R. prolixus molt and decreased its longevity while others showed no significant effects (Peterson et al., 2015). Interestingly, co-infection of R. prolixus with T. cruzi and Trypanosoma rangeli apparently decreases the negative effects of single infections, making insects more tolerant to higher amounts of parasites (Peterson et al., 2016). As seen, the harmful effects of T. cruzi are a result of multifarious interactions between parasite strain, insect species, nutritional state and environmental conditions. ...
Article
Triatomines are hematophagous insects that feed on the blood of vertebrates from different taxa, but can occasionally also take fluids from invertebrate hosts, including other insects. During the blood ingestion process, these insects can acquire diverse parasites that can later be transmitted to susceptible vertebrates if they complete their development inside bugs. Trypanosoma cruzi, the etiological agent of Chagas disease, and Trypanosoma rangeli are protozoan parasites transmitted by triatomines, the latter only transmitted by Rhodnius spp. The present work makes an extensive revision of studies evaluating triatomine-trypanosome interaction, with special focus on Rhodnius prolixus interacting with the two parasites. The sequences of events encompassing the development of these trypanosomes inside bugs and the consequent responses of insects to this infection, as well as many pathological effects produced by the parasites are discussed.
... The e-value has been used for a number of decades and has repeatedly verified that matedness does significantly increase the fecundity. It has also been adopted by other laboratories examining the effects of trypanosomes on the general health of the insect (Daflon-Teixeira et al., 2009;Fellet et al., 2014;Peterson, 2015;Peterson et al., 2016). ...
Article
The study of copulation and the control of egg production in the blood-feeding insect, Rhodnius prolixus, continues to offer a fertile ground for the cultivation of new insights into the physiological processes associated with reproduction. We begin this paper by describing the male organs of copulation showing that the aedaegus contains a structure which may serve as part of a pumping mechanism or valve to enable the male to fully pack the vagina with his secretions. We then summarize previously published work which identifies possible sensory and chemical aids that can be used by the male as he forms a naked spermatophore within the vagina of the female. With respect to the control of egg production, published anatomical and endocrinological experiments give rise to the intriguing possibility that a vascular portal system exists in the head of this insect, and that this system explains why circulation is required for egg production. By documenting the steps taken by the male during copulation, and by providing a new paradigm to explain the control of egg production, this paper identifies some assumptions that need verification, and offers a foundation upon which future scientists can explore reproductive physiology in this incredible bug.
... Additionally, the majority of studies on triatomines infected with T. cruzi or T. rangeli used insects infected with just one of the parasite species per experiment, as opposed to directly comparing two treatment groups of insects infected with T. cruzi or T. rangeli in the same experiment. The few studies that have made the direct comparison, all carried out with R. prolixus, found negative effects in insects infected with either parasite (D' Alessandro and Mandel 1969, Fellet et al. 2014, Peterson et al. 2015b or have not found the effects to be significantly different (Añez et al. 1992). Thus, there is sufficient evidence to compare the relative pathogenicity of T. cruzi and T. rangeli only in experimentally infected R. prolixus. ...
Article
The phrase, "T. rangeli is pathogenic to its insect vector," is commonly found in peer-reviewed publications on the matter, such that it has become the orthodox view of this interaction. In a literature survey, we identified over 20 papers with almost the exact phrase and several others alluding to it. The idea is of particular importance in triatomine population dynamics and the study of vector-borne T. cruzi transmission, as it could mean that triatomines infected with T. rangeli have lower fitness than uninfected insects. Trypanosoma rangeli pathogenicity was first observed in a series of studies carried out over fifty years ago using the triatomine species Rhodnius prolixus. However, there are few studies of the effect of T. rangeli on its other vector species, and several of the studies were carried out with R. prolixus under non-physiological conditions. Here, we re-evaluate the published studies that led to the conclusion that T. rangeli is pathogenic to its vector, to determine whether or not this indeed is the "true" effect of T. rangeli on its triatomine vector.
Chapter
In this book chapter, we discuss the interactions between triatomines, two heteroxenous trypanosomatids—Trypanosoma cruzi, the etiologic agent of Chagas disease, and Trypanosoma rangeli, a sister species that is harmless to humans—and the diverse intestinal microbiota of triatomines, which include mutualistic symbionts. In order to colonize and proliferate, both species of trypanosomatids and their symbionts must survive the varying conditions in the different regions of the triatomine intestine. Trypanosoma cruzi multiplies mainly within the posterior midgut and in the rectum, where the infectious metacyclic trypomastigotes develop. In contrast, T. rangeli colonizes the whole intestinal tract, but predominantly the midgut, and subsequently invades and multiplies within the hemocoel, and then the salivary glands where metacyclogenesis occurs. The effect of triatomines on trypanosomes is evident in the differing susceptibility and refractoriness of different species/strains of triatomine to trypanosome infection. The diverse conditions in different regions of the triatomine intestine induce the development of specific forms of the trypanosomatids, which are also affected by the nutritional status of their triatomine vector, that is, by feeding and starvation. Reciprocally, the effect of the trypanosomatids on their triatomine vectors is strong in some T. rangeli-Rhodnius combinations, but is dependent on stressful conditions in T. cruzi infections of triatomines. Ingestion of blood-stage trypomastigotes induces intestinal humoral immunity, which in turn modifies the populations of bacteria present in the triatomine intestinal tract.
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Triatominae bugs are the vectors of Chagas disease, a major concern to public health especially in Latin America, where vector-borne Chagas disease has undergone resurgence due mainly to diminished triatomine control in many endemic municipalities. Although the majority of Triatominae species occurs in the Americas, species belonging to the genus Linshcosteus occur in India, and species belonging to the Triatoma rubrofasciata complex have been also identified in Africa, the Middle East, South-East Asia, and in the Western Pacific. Not all of Triatominae species have been found to be infected with Trypanosoma cruzi, but the possibility of establishing vector transmission to areas where Chagas disease was previously non-endemic has increased with global population mobility. Additionally, the worldwide distribution of triatomines is concerning, as they are able to enter in contact and harbor other pathogens, leading us to wonder if they would have competence and capacity to transmit them to humans during the bite or after successful blood feeding, spreading other infectious diseases. In this review, we searched the literature for infectious agents transmitted to humans by Triatominae. There are reports suggesting that triatomines may be competent vectors for pathogens such as Serratia marcescens, Bartonella, and Mycobacterium leprae, and that triatomine infection with other microrganisms may interfere with triatomine-T. cruzi interactions, altering their competence and possibly their capacity to transmit Chagas disease.
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SUMMARY The transmission of parasites can be influenced by their co-occurrence with other parasites, in some cases increasing or reducing transmission. Trypanosoma cruzi , aetiologic agent of Chagas disease, often co-occurs with Trypanosoma rangeli , a parasite not pathogenic for mammal hosts. Both parasites can reduce the fitness of their insect vectors (the triatomine bugs; Hemiptera: Reduviidae), with T. rangeli being more pathogenic for some species. Here, we study the prevalence of T. cruzi and T. rangeli in the triatomine Rhodnius pallescens across a heterogeneously transformed landscape in Panamá. We found that single T. rangeli infections were more common in contiguously forested habitats, while single T. cruzi infections predominated in anthropogenically disturbed habitats. Trypanosoma cruzi–T. rangeli co-infections were more common in contiguous forests and in peridomiciliary areas. Furthermore, adult insects were more likely to be co-infected than nymphs. Our results suggest that human-mediated landscape transformation might have increased the predominance of single infections with T. cruzi within vectors. An important mechanism driving changes in trypanosome infection patterns in triatomines at a landscape scale includes alterations in host species composition that may vary with different degrees of deforestation. Trypanosome co-infection may also confer a survival advantage for R. pallescens to and/or throughout adulthood.
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The comparison among specimens of Rhodnius prolixus, at different stages of development, exposed to infections by Trypanosoma rangeli and Trypanosoma cruzi, revealed that the bugs exposed to T. cruzi showed a significant higher susceptibility to infection than that observed in the groups exposed to T. rangeli or to the mixture of both parasites. The similar mortality rate recorded in uninfected and T. cruzi infected bugs confirms that this parasite is harmless to R. prolixus. On the other hand. T. rangeli produces its pathological effect although the bugs ingest a relatively low number of flagellates. suggesting the existen ce of a direct relation between the amount of ingested parasites and the mortality produced. In mixed infection, T. cruzi does not inhibit the harmful effect ofT. rangeli on R. prolixus. The life cyc1e of R. prolixus is not affected by high infection of T. cruzi or low infection by T. range~. However, when bugs ingested a high amount of flagellates ofT. rangeli in mixed infections, the time to reach the adult stage in relation to controls, was significantIy longer. The epidemiological significance of the present results is discussed.
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SUMMARY The transmission of parasites can be influenced by their co-occurrence with other parasites, in some cases increasing or reducing transmission. Trypanosoma cruzi , aetiologic agent of Chagas disease, often co-occurs with Trypanosoma rangeli , a parasite not pathogenic for mammal hosts. Both parasites can reduce the fitness of their insect vectors (the triatomine bugs; Hemiptera: Reduviidae), with T. rangeli being more pathogenic for some species. Here, we study the prevalence of T. cruzi and T. rangeli in the triatomine Rhodnius pallescens across a heterogeneously transformed landscape in Panamá. We found that single T. rangeli infections were more common in contiguously forested habitats, while single T. cruzi infections predominated in anthropogenically disturbed habitats. Trypanosoma cruzi–T. rangeli co-infections were more common in contiguous forests and in peridomiciliary areas. Furthermore, adult insects were more likely to be co-infected than nymphs. Our results suggest that human-mediated landscape transformation might have increased the predominance of single infections with T. cruzi within vectors. An important mechanism driving changes in trypanosome infection patterns in triatomines at a landscape scale includes alterations in host species composition that may vary with different degrees of deforestation. Trypanosome co-infection may also confer a survival advantage for R. pallescens to and/or throughout adulthood.
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Rhodtestolin is a cardio-inhibitor that was first discovered in testes extracts of the blood-feeding insect, Rhodnius prolixus. Its role in reproduction remains unconfirmed, but if delivered to the female during spermatophore formation, it may serve to calm the female and/or relax the vaginal muscles to facilitate delivery and storage of the spermatophore. We describe here the anatomy of reproductive organs in R. prolixus and show that rhodtestolin is present in a low-molecular weight fraction of testes extracts separated by gel filtration, as well as in spermatophores delivered to the female during spermatophore formation. We also report that a rhodtestolin-like factor is present in the testes of R. brethesi, Triatoma dimidiata, T. klugi and Nesotriatoma bruneri, other Reduviidae, which are vectors of Chagas disease. Male secretions in insects are known to modify female behavior after copulation, and the presence of rhodtestolin in several genera of Reduviidae suggests that it plays an important role in reproductive success. Determining this role could lead to developing additional population control strategies for these bugs.
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Data on the distribution of triatomine species are usually obtained from the detection of peridomestic/domestic colonies, focal sampling of sylvatic populations, and information on the domestic intrusion of wild adult forms. Consequently, the more the synanthropic process of a Chagas disease vector is advanced, the more its geographic range may be precisely known. Thus, the past and recent changes in the geographic range of the most efficient vectors of T. cruzi to humans are well-known. However, an incomplete knowledge of species distribution exists when these organisms are restricted to sylvatic environments. It is unfeasible to systematically sample over wide areas because it is difficult to access certain types of ecotopes, thus making it difficult to investigate these areas. Moreover, in the case of exclusively sylvatic species, the sampling is generally random and, consequently, often unproductive. Finally, the sampled subsets are considered isolated species when they may represent components of an unknown continuous population. This chapter presents a review of the geographic distribution of Triatominae considering the species of epidemiological importance or the groups of species in which at least one species has an epidemiological significance as a vector of Trypanosoma cruzi to humans. All the species considered belong to the tribes Rhodniini and Triatomini.
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It is often assumed that parasites are not virulent to their vectors. Nevertheless, parasites commonly exploit their vectors (nutritionally for example) so these can be considered a form of host. Trypanosoma cruzi, a protozoan found in mammals and triatomine bugs in the Americas, is the etiological agent of Chagas disease that affects man and domestic animals. While it has long been considered avirulent to its vectors, a few reports have indicated that it can affect triatomine fecundity. We tested whether infection imposed a temperature-dependent cost on triatomine fitness. We held infected insects at four temperatures between 21 and 30°C and measured T. cruzi growth in vitro at the same temperatures in parallel. Trypanosoma cruzi infection caused a considerable delay in the time the insects took to moult (against a background effect of temperature accelerating moult irrespective of infection status). Trypanosoma cruzi also reduced the insects' survival, but only at the intermediate temperatures of 24 and 27°C (against a background of increased mortality with increasing temperatures). Meanwhile, in vitro growth of T. cruzi increased with temperature. Our results demonstrate virulence of a protozoan agent of human disease to its insect vector under these conditions. It is of particular note that parasite-induced mortality was greatest over the range of temperatures normally preferred by these insects, probably implying adaptation of the parasite to perform well at these temperatures. Therefore we propose that triggering this delay in moulting is adaptive for the parasites, as it will delay the next bloodmeal taken by the bug, thus allowing the parasites time to develop and reach the insect rectum in order to make transmission to a new vertebrate host possible.
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Introducción. Los estudios genéticos en Trypanosoma cruzi han buscado establecer asociaciones de variantes genéticas del parásito con manifestaciones clínicas de la enfermedad, origen biológico y geográfico de los aislamientos; sin embargo, los resultados de asociación con los marcadores comúnmente usados en estos estudios han generado mucha controversia, principalmente en la asociación de grupos con características clínicas y epidemiológicas de la enfermedad. Objetivo. Se planteó determinar la variabilidad de genes que codifican para las proteínas tripanotión reductasa y cruzipaína, involucradas en mecanismos de infección y supervivencia del parásito en el hospedador mamífero, y probar la asociación de variantes génicas con origen biológico y geográfico de cepas colombianas de T. cruzi. Materiales y métodos. Se tipificaron por reacción en cadena de la polimerasa- polimorfismo de longitud del fragmento de restricción seis SNPs (Single Nucleotide Polymorphisms) en tripanotión reductasa y ocho SNPs en cruzipaína en 36 cepas colombianas de T. cruzi de diferentes regiones y origen biológico. Resultados. Con las enzimas Acy I y Hae III se determinaron tres genotipos para tripanotión reductasa. Para cruzipaína se identificaron seis genotipos con las enzimas Rsa I, Ban I y Bsu 36I. Conclusiones. Para tripanotión reductasa no fue posible establecer una asociación con el origen biológico o geográfico; sin embargo los alelos producidos en las posiciones 102 y 210, permitieron discriminar los grupos tradicionales I y II. Con los genotipos obtenidos para cruzipaína se establecieron relaciones a estos grupos, origen biológico y geográfico. Los resultados sugieren la utilidad de estos genes como marcadores moleculares para determinar y diferenciar variedades genéticas en T. cruzi.
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Flight dispersal of the triatomine bug species Rhodnius pallescens Barber, the principal vector of Chagas disease in Panama, is an important mechanism for spreading Trypanosoma cruzi, causative agent of Chagas disease. This study measures R. pallescens flight performance using a tethered flight mill both when uninfected, and when infected with T. cruzi or Trypanosoma rangeli. Forty-four out of the 48 (91.7%) insects initiated flight across all treatments, and trypanosome infection did not significantly impact flight initiation. Insects from all treatments flew a cumulative distance ranging from 0.5 to 5 km before fatiguing. The median cumulative distance flown before insect fatigue was higher in T. cruzi- and T. rangeli-infected insects than in control insects; however, this difference was not statistically significant. There was a positive relationship between parasite load ingested and time until flight initiation in T. rangeli-infected bugs, and T. rangeli- and T. cruzi-infected females flew significantly faster than males at different time points. These novel findings allow for a better understanding of R. pallescens dispersal ability and peridomestic management strategies for the prevention of Chagas disease in Panama.
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The insect Rhodnius prolixus is responsible for the transmission of Trypanosoma cruzi, which is the etiological agent of Chagas disease in areas of Central and South America. Besides this, it can be infected by other trypanosomes such as Trypanosoma rangeli. The effects of these parasites on vectors are poorly understood and are often controversial so here we focussed on possible negative effects of these parasites on the reproductive performance of R. prolixus, specifically comparing infected and uninfected couples. While T. cruzi infection did not delay pre-oviposition time of infected couples at either temperature tested (25 and 30°C) it did, at 25°C, increase the e-value in the second reproductive cycle, as well as hatching rates. Meanwhile, at 30°C, T. cruzi infection decreased the e-value of insects during the first cycle and also the fertility of older insects. When couples were instead infected with T. rangeli, pre-oviposition time was delayed, while reductions in the e-value and hatching rate were observed in the second and third cycles. We conclude that both T. cruzi and T. rangeli can impair reproductive performance of R. prolixus, although for T. cruzi, this is dependent on rearing temperature and insect age. We discuss these reproductive costs in terms of potential consequences on triatomine behavior and survival.
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Rhodnius prolixus is an obligate haematophagous insect and one of the most important vectors of Trypanosoma cruzi, the causative agent of Chagas disease in the Americas. T. cruzi is a highly variable parasite which is not transmitted in the same efficiency by the different triatomine vectors. Because different T. cruzi genotypes are aetiopathologically divergent, further elucidation of the transmission abilities of different Chagas disease vectors is extremely important. In the present study, the growth behaviour of two T. cruzi isolates, MDID/BR/1993/C45 (TcI) and TBRA/BR/1999/JCA3 (TcII), sharing the same microhabitat (intestinal tract) in single and mixed infections, was examined. The distribution patterns and parasite population densities were evaluated at 7, 14 and 21 days after feeding (daf) by quantification of parasites using Neubauer haemocytometric measurements and mini-exon PCR to identify TcI and TcII subpopulations. Parasitic colonization in the small intestine was more successful in the mixed infection model than the single infection models at 21 daf. In the rectal lumen and wall, the growth behaviour of the mixed infection was similar to that of the TcI group, although the total parasite number was lower. In the TcII group, no metacyclic trypomastigote forms were found. PCR analysis of the contents of each dissected region showed different genotype fractions in the mixed infection model, in which TcI seemed to be the predominant isolate. The different growth behaviour of the TcI and TcII isolates in single and mixed infection models demonstrated that possibly an intraspecific factor modulates parasitic development in the intestine of R. prolixus.
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Introducción. La enfermedad de Chagas constituye un grave problema de salud publica en Latinoamérica; en Colombia existen en gran parte de su geografía las condiciones ecoepidemiológicas propicias para la transmisión activa de esta enfermedad. Objetivo. En este estudio fue evaluada una población del municipio de Morroa, departamento de Sucre, para identificar factores de riesgo y determinar la seroprevalencia a la enfermedad de Chagas. Materiales y métodos. A una muestra de 122 personas pertenecientes al área rural (n=76) y urbana (n=46), se les aplicó una encuesta epidemiológica y se les realizó un tamizaje serológico con la prueba Elisa, confirmación de seropositivos con hemoaglutinación indirecta (HAI) (Chagatest®) y reacción en cadena de la polimerasa (PCR) como prueba parasitológica confirmatoria. Resultados. Cuatro de las personas resultaron positivas para Elisa (3,28%); sin embargo, fueron negativas a HAI y PCR. La serología discordante fue definida con prueba de inmunofluorescencia indirecta (IFI), encontrándose una de las cuatro personas positivas. La población analizada mostró una baja presencia de anticuerpos anti-Trypanosoma cruzi. No fue posible determinar la presencia del parásito en sangre usando la prueba PCR. Los principales factores de riesgo presentes fueron casas con techos de palmas, piso de tierra, paredes de bahareque y madera, y la presencia de reservorios (animales domésticos). Conclusiones. Nuestros resultados indican que la zona estudiada presenta elementos de riesgo para el establecimiento de un ciclo de transmisión activa, se hace necesario verificar la presencia de triatominos en la zona de estudio y establecer medidas para prevenir la presencia de la enfermedad de Chagas en el área de Morroa, Sucre.
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From 148 substrate samples collected in peridomestic triatomine-infested habitats of 24 farms in Central Brazil, 31 isolates of Metarhizium anisopliae (Metsch.) Sorok. and 15 isolates of Beauveria bassiana (Bals.) Vuill. were obtained. Most of the isolates were found in substrates that consisted of soil mixed with animal feces or soil only in areas of trees where poultry roost and pig houses. Fungi were detected with an insect bait method using Triatoma infestans (Klug), and combined in vitro and in vivo techniques with modified Chase medium and T. infestans. All isolates were highly virulent to T. infestans third instar nymphs at a relative humidity > 98% and temperature of 25 ± 0.5°C. However, activity against nymphs was reduced at 75% relative humidity. Results underline the potential of B. bassiana and M. anisopliae as agents for biological control of vectors of Chagas disease. Both species occur naturally in peridomestic habitats of triatomines in Central Brazil and may contribute to control these vectors and to reduce the risk of reinfestation of houses after eliminating domestic vector species.
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This paper reports a study on the mycobiota in the digestive tract of four important species of triatomines: Rhodnius prolixus, R. neglectus, Diptelanogaster maximus and Panstrongylus megistus. The digestive tracts of 90 adults and 425 nymphs of these four triatomine species were studied and 365 fungal strains were isolated. The genera with the greatest number of species were Aspergillus, Penicillium (14 species in each genus), Acremonium and Cladosporium (three species in each genus), and the most frequent species, in decreasing order, were Aspergillus awamori, Penicillium corylophilum, Cladosporium herbarum and Aspergillus niger. It was concluded that, among the isolated fungi, Aspergillus niger and Penicillium corylophilum might be part of the natural flora of the digestive tract of triatomines.
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Mated females of Rhodnius prolixus lay eggs at approximately twice the rate of unmated females. Males which have had their seminal vesicles or opaque accessory glands removed produce spermatophores at mating, but no spermatozoa appear in the spermathecae of the females. The females involved in such matings do not exhibit an increase in eggproduction. When females lacking their spermathecae are mated to normal males, the increase in egg production which follows normal matings does not materialize. Implanting spermathecae from mated females into virgin females increases the egg-production of the host. Implanting spermathecae from virgin females or seminal vesicles or transparent accessory glands from males has no effect on the egg-production of the donor. It is tentatively concluded that a blood-borne factor from the spermathecae containing spermatozoa is the primary stimulus to increased egg production in a mated female.
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Food quality often has profound effects on life history traits and individual fitness, altering rates of growth and development, changing the timing of reproduction, and shifting the trade-off between egg size and egg number. Few data are available on the effects of food quality on copepod life history traits. We measured several life history traits on a large number of individuals to document the effects of food quality on individual traits, on life history correlates, and on a composite measure of individual fitness in the freshwater copepod Boeckella triarticulata Thomson. Nauplii were raised individually on two diets: one consisted of the high quality alga Cryptomonas sp. (abbreviated as CR), and the second diet consisted of a combination of Cryptomonas sp. and the low quality cyanobacterium Anabaena flos-aquae (CA). The mixed CA diet slowed growth and development so that individuals raised on this diet were Older and smaller at metamorphosis and maturity. Despite these effects, there were no differences between diets in survival to maturity, and male copepods raised on the mixed diet lived significantly longer than females or than either sex raised on Cryptomonas alone. Females raised on the mixed diet produced more and larger clutches than those raised on CR, so that total egg production increased on this diet, although large intradiet variation obscured statistical differences between diets in these parameters. Intradiet variation was due to a large range in the number of clutches produced by individual females: some individuals produced 10-15 clutches, contradicting previous descriptions of this species as semelparous. Although diet affected age at first reproduction, it had no significant effect on individual fitness, estimated as λ. Boeckella triarticulata achieved high fitness either by minimizing age at first reproduction (CR diet) or by increasing reproductive output (CA diet). Data collected from cast-off exuviae allow nondestructive measures of individual life history traits along with a composite measure of individual fitness. Combining these two analyses is an important step in unraveling life history correlates and in identifying the selective forces driving life history evolution in these crustaceans.
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The purpose of this study was to calculate the seroprevalence of Trypanosoma cruzi infection in a sample of inhabitants from a region considered to be at high risk of natural transmission of Chagas disease in Colombia. A cross-sectional study was conducted in subjects from 5 municipalities, recruited in urban and rural locations, distributed by gender according to the demographic information available. Socio-demographic information, history of potential exposure to insect vectors, blood donating, as well as symptoms suggesting cardiac disease were collected using a questionnaire. After giving written informed consent, blood specimens were obtained from 486 people to determine the serologic evidence of past exposure to T. cruzi. Infection was diagnosed when two different tests (ELISA and IHA) were positive. The seroprevalence of antibodies against T. cruzi was 16.91% considering an estimated population of 44,355 aged between 15 and 89 years (95%IC: 13.72 to 20.01). The factors significantly associated with the infection were: 1- Housing materials like vegetable material, adobe or unfinished brick walls; 2- The fact of having previous tests for Chagas disease (regardless of the result). Of note, the mean ages among infected and not infected participants were significantly different (49.19 vs. 41.66, p≤0.0001). Among the studied municipalities, the one with the highest frequency of T. cruzi infection was Nunchia, with 31.15% of the surveyed subjects. Therefore it may be concluded that T. cruzi infection is highly prevalent in the north region of Casanare, in Colombia.
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The course of Trypanosom cruzi Chagas infection was studied in Panstrongylus megistus (Burmeister) in the laboratory. We analyzed the number of ecdyses, mortality, and reproduction of this triatomine in relation to parasitemia. For infection, first and second instars of P. megistus were allowed to feed on albino mice infected with the VLE-95 strain of T. cruzi. The following reproductive parameters were investigated: egg production, fertility, number of fertile eggs that did not hatch, number of daughter nymphs that presented congenital alterations, number of matings of each couple, and life span of females. The results showed that the parasite did not alter the nymphal development (P > 0.05) and ecdyses (P > 0.05) of the triatomine. However, reproduction was significantly reduced in terms of all the items studied (P < 0.01 to P < 0.0001) except for the number of matings (P > 0.05) and for the number of daughter nymphs that presented congenital alterations (P > 0.05).
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Background Usually the analysis of the various developmental stages of Trypanosoma cruzi in the experimentally infected vertebrate and invertebrate hosts is based on the morphological observations of tissue fragments from animals and insects. The development of techniques that allow the imaging of animals infected with parasites expressing luciferase open up possibilities to follow the fate of bioluminescent parasites in infected vectors. Methods D-luciferin (60 μg) was injected into the hemocoel of the whole insect before bioluminescence acquisition. In dissected insects, the whole gut was incubated with D-luciferin in PBS (300 μg/ml) for ex vivo bioluminescence acquisition in the IVIS® Imaging System, Xenogen. Results Herein, we describe the results obtained with the luciferase gene integrated into the genome of the Dm28c clone of T. cruzi, and the use of these parasites to follow, in real time, the infection of the insect vector Rhodnius prolixus, by a non- invasive method. The insects were evaluated by in vivo bioluminescent imaging on the feeding day, and on the 7 th, 14 th, 21 st and 28 th days after feeding. To corroborate the bioluminescent imaging made in vivo, and investigate the digestive tract region, the insects were dissected. The bioluminescence emitted was proportional to the number of protozoans in regions of the gut. The same digestive tracts were also macerated to count the parasites in distinct morphological stages with an optical microscope, and for bioluminescence acquisition in a microplate using the IVIS® Imaging System. A positive correlation of parasite numbers and bioluminescence in the microplate was obtained. Conclusions This is the first report of bioluminescent imaging in Rhodnius prolixus infected with trypomastigotes of the Dm28c-luc stable strain, expressing firefly luciferase. In spite of the distribution limitations of the substrate (D-luciferin) in the insect body, longitudinal evaluation of infected insects by bioluminescent imaging is a valuable tool. Bioluminescent imaging of the digestive tract infected with Dm28c-luc is highly sensitive and accurate method to track the fate of the parasite in the vector, in the crop, intestine and rectum. This methodology is useful to gain a better understanding of the parasite – insect vector interactions.
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Fitness is a vague, poorly developed concept in ecology and evolutionary biology. Although it is generally recognized that fitness is determined by the complete survival and reproductive schedules of individual organisms, experimental studies have rarely attempted to integrate these into a single measure of individual fitness. Instead, particularly in studies of natural selection, components of fitness are measured as surrogates for fitness. In this article, we develop an integrated measure of fitness based on the philosophical underpinnings provided by the notion of propensity fitness, combined with classical demographic methods. We show how life-history data, collected for an individual, can be formatted as an age-structured population projection matrix, A((m)). The dominant eigenvalue, lambda((m)), of this matrix is an estimate of that individual's propensity fitness. Using life-history data sets on European sparrowhawks and blue tits, we show that the interpretation of analyses of selection can shi
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Trypanosoma cruzi in order to complete its development in the digestive tract of Rhodnius prolixus needs to overcome the immune reactions and microbiota trypanolytic activity of the gut. We demonstrate that in R. prolixus following infection with epimastigotes of Trypanosoma cruzi clone Dm28c and, in comparison with uninfected control insects, the midgut contained (i) fewer bacteria, (ii) higher parasite numbers, and (iii) reduced nitrite and nitrate production and increased phenoloxidase and antibacterial activities. In addition, in insects pre-treated with antibiotic and then infected with Dm28c, there were also reduced bacteria numbers and a higher parasite load compared with insects solely infected with parasites. Furthermore, and in contrast to insects infected with Dm28c, infection with T. cruzi Y strain resulted in a slight decreased numbers of gut bacteria but not sufficient to mediate a successful parasite infection. We conclude that infection of R. prolixus with the T. cruzi Dm28c clone modifies the host gut immune responses to decrease the microbiota population and these changes are crucial for the parasite development in the insect gut.
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Chagas disease transmission risk is a function of the presence of triatomines in domestic habitats. Rhodnius ecuadoriensis is one of the main vectors implicated in transmission of Trypanosoma cruzi in Ecuador. This triatomine species is present in domestic, peridomestic and sylvatic habitats in the country. To determine the distribution of sylvatic populations of R. ecuadoriensis and the factors related to this distribution, triatomine searches were conducted between 2005 and 2009 in southern Ecuador. Manual triatomine searches were conducted by skilled bug collectors in 23 communities. Sylvatic searched sites were selected by a) directed sampling, where microhabitats were selected by the searchers and b) random sampling, where sampling points where randomly generated. Domiciliary triatomine searches were conducted using the one man-hour method. Natural trypanosome infection was determined by microscopic examination and PCR. Generalized linear models were used to test the effect of environmental factors on the presence of sylvatic triatomines. In total, 1,923 sylvatic individuals were collected representing a sampling effort of 751 man-hours. Collected sylvatic triatomines were associated with mammal and bird nests. The 1,219 sampled nests presented an infestation index of 11.9%, a crowding of 13 bugs per infested nest, and a colonization of 80% of the nests. Triatomine abundance was significantly higher in squirrel (Sciurus stramineus) nests located above five meters from ground level and close to the houses. In addition, 8.5% of the 820 examined houses in the same localities were infested with triatomines. There was a significant correlation between R. ecuadoriensis infestation rates found in sylvatic and synanthropic environments within communities (p = 0.012). Parasitological analysis revealed that 64.7% and 15.7% of the sylvatic bugs examined (n = 300) were infected with Trypanosoma cruzi and T. rangeli respectively, and 8% of the bugs presented mixed infections. The wide distribution of sylvatic R. ecuadoriensis populations may jeopardize the effectiveness of control campaigns conducted to eliminate domestic populations of this species. Also, the high T. cruzi infection rates found in sylvatic R. ecuadoriensis populations in southern Ecuador could constitute a risk for house re-infestation and persistent long-term Chagas disease transmission in the region.
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Rhodnius prolixus is a blood-feeding insect that can transmit Trypanosoma cruzi and Trypanosoma rangeli to vertebrate hosts. Recently, genomic resources for invertebrate vectors of human pathogens have increased significantly, and R. prolixus has been one of the main species studied among the triatomines. However, the paucity of information on many of the fundamental molecular aspects of this species limits the use of the available genomic information. The present study aimed to facilitate gene expression studies by identifying the most suitable reference genes for the normalization of mRNA expression data from qPCR. The expression stability of five candidate reference genes (18S rRNA, GAPDH, β-actin, α-tubulin and ribosomal protein L26) was evaluated by qPCR in two tissues (salivary gland and intestine) and under different physiological conditions: before and after blood feeding and after infection with T. cruzi or T. rangeli. The results were analyzed with three software programs: geNorm, NormFinder and BestKeeper. All of the evaluated candidate genes proved to be acceptable as reference genes, but some were found to be more appropriate depending on the experimental conditions. 18S, GAPDH and α-tubulin showed acceptable stability for studies in all of the tissues and experimental conditions evaluated. β-actin, one of the most widely used reference genes, was confirmed to be one of the most suitable reference genes in studies with salivary glands, but it had the lowest expression stability in the intestine after insect blood feeding. L26 was identified as the poorest reference gene in the studies performed. The expression stability of the genes varies in different tissue samples and under different experimental conditions. The results provided by three statistical packages emphasize the suitability of all five of the tested reference genes in both the crop and the salivary glands with a few exceptions. The results emphasise the importance of validating reference genes for qRT-PCR analysis in R. prolixus studies.
Book
This is a book for statistical practitioners, particularly those who design and analyze studies for survival and event history data. Its goal is to extend the toolkit beyond the basic triad provided by most statistical packages: the Kaplan-Meier estimator, log-rank test, and Cox regression model. Building on recent developments motivated by counting process and martingale theory, it shows the reader how to extend the Cox model to analyse multiple/correlated event data using marginal and random effects (frailty) models. It covers the use of residuals and diagnostic plots to identify influential or outlying observations, assess proportional hazards and examine other aspects of goodness of fit. Other topics include time-dependent covariates and strata, discontinuous intervals of risk, multiple time scales, smoothing and regression splines, and the computation of expected survival curves. A knowledge of counting processes and martingales is not assumed as the early chapters provide an introduction to this area. The focus of the book is on actual data examples, the analysis and interpretation of the results, and computation. The methods are now readily available in SAS and S-Plus and this book gives a hands-on introduction, showing how to implement them in both packages, with worked examples for many data sets. The authors call on their extensive experience and give practical advice, including pitfalls to be avoided. Terry Therneau is Head of the Section of Biostatistics, Mayo Clinic, Rochester, Minnesota. He is actively involved in medical consulting, with emphasis in the areas of chronic liver disease, physical medicine, hematology, and laboratory medicine, and is an author on numerous papers in medical and statistical journals. He wrote two of the original SAS procedures for survival analysis (coxregr and survtest), as well as the majority of the S-Plus survival functions. Patricia Grambsch is Associate Professor in the Division of Biostatistics, School of Public Health, University of Minnesota. She has collaborated extensively with physicians and public health researchers in chronic liver disease, cancer prevention, hypertension clinical trials and psychiatric research. She is a fellow the American Statistical Association and the author of many papers in medical and statistical journals.
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Food quality often has profound effects on life history traits and individual fitness, altering rates of growth and development, changing the timing of reproduction, and shifting the trade-off between egg size and egg number. Few data are available on the effects of food quality on copepod life history traits. We measured several life history traits on a large number of individuals to document the effects of food quality on individual traits, on life history correlates, and on a composite measure of individual fitness in the freshwater copepod Boeckella triarticulata Thomson. Nauplii were raised individually on two diets: one consisted of the high quality alga Cryptomonas sp. (abbreviated as CR), and the second diet consisted of a combination of Cryptomonas sp. and the low quality cya- nobacterium Anabaena flos-aquae (CA). The mixed CA diet slowed growth and develop- ment so that individuals raised on this diet were older and smaller at metamorphosis and maturity. Despite these effects, there were no differences between diets in survival to maturity, and male copepods raised on the mixed diet lived significantly longer than females or than either sex raised on Cryptomonas alone. Females raised on the mixed diet produced more and larger clutches than those raised on CR, so that total egg production increased on this diet, although large intradiet variation obscured statistical differences between diets in these parameters. Intradiet variation was due to a large range in the number of clutches produced by individual females: some individuals produced 10-15 clutches, contradicting previous descriptions of this species as semelparous. Although diet affected age at first reproduction, it had no significant effect on individual fitness, estimated as X. Boeckella triarticulata achieved high fitness either by minimizing age at first reproduction (CR diet) or by increasing reproductive output (CA diet). Data collected from cast-off exuviae allow nondestructive measures of individual life history traits along with a composite measure of individual fitness. Combining these two analyses is an important step in unraveling life history correlates and in identifying the selective forces driving life history evolution in these crustaceans.
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A guide to using S environments to perform statistical analyses providing both an introduction to the use of S and a course in modern statistical methods. The emphasis is on presenting practical problems and full analyses of real data sets.
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Concomitant infections are common in nature and often involve parasites. A number of examples of the interactions between protozoa and viruses, protozoa and bacteria, protozoa and other protozoa, protozoa and helminths, helminths and viruses, helminths and bacteria, and helminths and other helminths are described. In mixed infections the burden of one or both the infectious agents may be increased, one or both may be suppressed or one may be increased and the other suppressed. It is now possible to explain many of these interactions in terms of the effects parasites have on the immune system, particularly parasite-induced immunodepression, and the effects of cytokines controlling polarization to the Th1 or Th2 arms of the immune response. In addition, parasites may be affected, directly or indirectly, by cytokines and other immune effector molecules and parasites may themselves produce factors that affect the cells of the immune system. Parasites are, therefore, affected when they themselves, or other organisms, interact with the immune response and, in particular, the cytokine network. The importance of such interactions is discussed in relation to clinical disease and the development and use of vaccines.
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Here we present Primer3Plus, a new web interface to the popular Primer3 primer design program as an enhanced alternative for the CGI- scripts that come with Primer3. Primer3 consists of a command line program and a web interface. The web interface is one large form showing all of the possible options. This makes the interface powerful, but at the same time confusing for occasional users. Primer3Plus provides an intuitive user interface using present-day web technologies and has been developed in close collaboration with molecular biologists and technicians regularly designing primers. It focuses on the task at hand, and hides detailed settings from the user until these are needed. We also added functionality to automate specific tasks like designing primers for cloning or step-wise sequencing. Settings and designed primer sequences can be stored locally for later use. Primer3Plus supports a range of common sequence formats, such as FASTA. Finally, primers selected by Primer3Plus can be sent to an order form, allowing tight integration into laboratory ordering systems. Moreover, the open architecture of Primer3Plus allows easy expansion or integration of external software packages. The Primer3Plus Perl source code is available under GPL license from SourceForge. Primer3Plus is available at http://www.bioinformatics.nl/primer3plus.
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The effect of a parasite on the life history of its vector is important for understanding and predicting disease transmission. Chagas disease agent Trypanosoma cruzi is a generalist parasite that is diverse across scales from its genetic diversity to the 100s of mammal and vector species it infects. Its vertebrate hosts show quite variable responses to infection, however, to date there are no studies looking at how T. cruzi variability might result in variable outcomes in its invertebrate host. Therefore, we investigated the effect of different T. cruzi I strains on Rhodnius prolixus survival and development. We found significant variation between insects infected with different strains, with some strains having no effect, as compared with uninfected insects, and others with significantly lower survival and development. We also found that different variables had varying importance between strains, with the effect of time postinfection and the blood:weight ratio of the infective meal significantly affecting the survival of insects infected with some strains, but not others. Our results suggest that T. cruzi can be pathogenic not only to its vertebrate hosts but also to its invertebrate hosts. © The American Society of Tropical Medicine and Hygiene.
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Triatoma virus (TrV) is the only triatomine entomopathogenic virus identified so far. Propagation of TrV in insectaries depends on handling procedures and triatomine population dynamics. The effects of propagation can be devastating and entire colonies must often be sacrificed to prevent spread of the virus throughout the insectary. This study found that after 41.3 days from TrV ingestion of human blood with 0.04 mg of viral protein by 5th instar Triatomainfestans, viral particles could be detected by RT-PCR; in a second horizontal transmission experiment time to detection resulted in a mean of 42.5 days. These results should rise awareness of TrV dynamics in nature, help estimate the spread of this virus when TrV-infected field-collected insects are incorporated into an insectary, and provide a base for the consideration of TrV as an agent of biological control of some species of triatomines.
Book
Introduction.- Estimating the Survival and Hazard Functions.- The Cox Model.- Residuals.- Functional Form.- Testing Proportional Hazards.- Influence.- Multiple Events per Subject.- Frailty Models.- Expected Survival.
Article
Trypanosoma cruzi (T. cruzi), the etiological agent of Chagas disease, affects nearly 18 million people in Latin America and 90 million are at risk of infection. The parasite presents two stages of medical importance in the host, the amastigote, intracellular replicating form, and the extracellular trypomastigote, the infective form. Thus infection by T. cruzi induces a complex immune response that involves effectors and regulatory mechanisms. That is why control of the infection requires a strong humoral and cellular immune response; hence, the outcome of host-parasite interaction in the early stages of infection is extremely important. A critical event during this period of the infection is innate immune response, in which the macrophage's role is vital. Thus, after being phagocytized, the parasite is able to develop intracellularly; however, during later periods, these cells induce its elimination by means of toxic metabolites. In turn, as the infection progresses, adaptive immune response mechanisms are triggered through the TH1 and TH2 responses. Finally, T. cruzi, like other protozoa such as Leishmania and Toxoplasma, have numerous evasive mechanisms to the immune response that make it possible to spread around the host. In our Laboratory we have developed a vaccination model in mice with Trypanosoma rangeli, nonpathogenic to humans, which modulates the immune response to infection by T. cruzi, thus protecting them. Vaccinated animals showed an important innate response (modulation of NO and other metabolites, cytokines, activation of macrophages), a strong adaptive cellular response and significant increase in specific antibodies. The modulation caused early elimination of the parasites, low parasitaemia, the absence of histological lesions and high survival rates. Even though progress has been made in the knowledge of some of these mechanisms, new studies must be conducted which could target further prophylactic and therapeutic trials against T. cruzi infection.
Article
Chagas’ disease, endemic in Latin America, is spread in natural environments through animal reservoirs, including marsupials, mice and guinea pigs. Farms breeding guinea pigs for food are located in some Latin-American countries with consequent risk of digestive infection. The aim of this work was to study the effect of vaccination with Trypanosoma rangeli in guinea pigs challenged with Trypanosoma cruzi. Animals were vaccinated with fixated epimastigotes of T. rangeli, emulsified with saponin. Controls received only PBS. Before being challenged with T. cruzi, parasitemia, survival rates and histological studies were performed. The vaccinated guinea pigs revealed significantly lower parasitemia than controls (p < 0.0001–0.01) and a discrete lymphomonocytic infiltrate in cardiac and skeletal muscles was present. In the chronic phase, the histological view was normal. In contrast, control group revealed amastigote nests and typical histopathological alterations compatible with chagasic myocarditis, endocarditis and pericarditis. These results, together with previous works in our laboratory, show that T. rangeli induces immunoprotection in three species of animals: mice, guinea pigs and dogs. The development of vaccines for use in animals, like domestic dogs and guinea pigs in captivity, opens up new opportunities for preventive tools, and could reduce the risk of infection with T. cruzi in the community.
Article
Yolk deposition begins in the terminal oocytes of virgins of Triatoma protracta a few days after adult eclosion, and while a few eggs may be matured before vitellogenesis ceases, none are laid. Mating at day four stimulates egg maturation and oviposition in fed and unfed females, egg-laying beginning as early as nine days after eclosion. If mating is delayed until day 16, by which time vitellogenesis normally has ceased, stored eggs are laid within two to four days and yolk deposition is resumed. Removal of the brain prevents oviposition, as does the severance of the ventral nerve cord. Thus, an intact central nervous system is required for egg-laying. Also, since neither operation inhibits egg maturation or ovulation, it appears that the latter reproductive responses to mating are independent of oviposition.
Article
A class of linear rank statistics is proposed for the k-sample problem with right-censored survival data. The class contains as special cases the log rank test (Mantel, 1966; Cox, 1972) and a test essentially equivalent to Peto & Peto's (1972) generalization of the Wilcoxon test. Martingale theory is used to establish asymptotic normality of test statistics under the null hypotheses considered, and to derive expressions for asymptotic relative efficiencies under contiguous sequences of alternative hypotheses. A class of distributions is presented which corresponds to the class of rank statistics in the sense that for each distribution there is a statistic with some optimal properties for detecting location alternatives from that distribution. Some Monte Carlo results are displayed which present small sample behaviour.
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The analysis of censored failure times is considered. It is assumed that on each individual are available values of one or more explanatory variables. The hazard function (age-specific failure rate) is taken to be a function of the explanatory variables and unknown regression coefficients multiplied by an arbitrary and unknown function of time. A conditional likelihood is obtained, leading to inferences about the unknown regression coefficients. Some generalizations are outlined. LIFEtables are one of the oldest statistical techniques and are extensively used by medical statisticians and by actuaries. Yet relatively little has been written about their more formal statistical theory. Kaplan and Meier (1958) gave a comprehensive review of earlier work and many new results. Chiang in a series of papers has, in particular, explored the connection with birth-death processes; see, for example, Chiang (1968). The present paper is largely concerned with the extension of the results of Kaplan and Meier to the comparison of life tables and more generally to the incorporation of regression-like arguments into life-table analysis. The arguments are asymptotic but are relevant to situations where the sampling fluctuations are large enough to be of practical importance. In other words, the applications are more likely to be in industrial reliability studies and in medical statistics than in actuarial science. The procedures proposed are, especially for the two-sample problem, closely related to procedures for combining contingency tables; see Mantel and Haenzel (1959), Mantel (1963) and, especially for the application to life tables, Mantel (1966). There is also a strong connection with a paper read recently to the Society by R. and J. Peto (1972). We consider a population of individuals; for each individual we observe either the time to "failure" or the time to ccloss" or censoring. That is, for the censored individuals we know only that the time to failure is greater than the censoring time. Denote by T a random variable representing failure time; it may be discrete or continuous. Let F(t) be the survivor function, %(t) = pr (T2 t)
Article
The analysis of censored failure times is considered. It is assumed that on each individual are available values of one or more explanatory variables. The hazard function (age‐specific failure rate) is taken to be a function of the explanatory variables and unknown regression coefficients multiplied by an arbitrary and unknown function of time. A conditional likelihood is obtained, leading to inferences about the unknown regression coefficients. Some generalizations are outlined.
Article
The product (R) of the weight of the blood meal and the initial weight of the insect is shown to be a reliable predictor of egg production. The egg production efficiency (E), defined as the number of eggs produced per R, has a value characteristic of virgin females, and another, higher, value characteristic of mated females. Topical applications of C18 JH or Altosid to virgin females increase the value of E to the mated level in a fashion which suggests that these compounds act via a trigger mechanism. These compounds do not affect the rate at which oviposition occurs.
Article
The causes of the particular distribution of both Trypanosoma cruzi lineages throughout the American continent remain unknown. In Colombia, T. cruzi I is the predominant group in both domestic and sylvatic cycles. Here, we present the biological characterization of T. cruzi parasites belonging to both T. cruzi I and T. cruzi IIb groups. Our results show the inability of the T. cruzi IIb clones to infect mammalian cells, produce trypomastigotes and replicate in Rhodnius prolixus, the main vector species in this country. Moreover, this result was confirmed when other species from the same genus, such as R. pallescens and R. robustus, were infected with the same TcIIb clone and its parental strain, while the infection in other genera such as Triatoma and Panstrongylus was successful. Furthermore, the growth kinetics and duplication time in vitro suggest that the high prevalence of T. cruzi I in Colombia results from more successful interactions between parasite lineage, vector, and host species. This type of study may help to understand the factors influencing the particular epidemiological patterns of Chagas disease transmission in different endemic regions.
Article
1.1. The pathogenicity of flagellates to their invertebrate hosts is discussed.2.2. The pathogenicity of T. rangeli to R. prolixus is found to be heavy in the first nymphal instars. Bugs with infection in the hemolymph were unable to molt.3.3. The pathogenicity of T. rangeli in the bed bug, C. lectularius, was found to be greater than in R. prolixus. Invasion of the hemolymph was fairly rapid.4.4. Bugs with a heavy infection in the hemolymph carried a higher mortality than those with lighter infection.5.5. Mortality is probably not connected with the penetration of the gut wall, since it occurs in bugs infected directly into the hemolymph. Preliminary studies indicate that the deficiency in the concentration of certain amino acids interferes with the molting process in the infected bugs.
Article
Vargas, N., Souto, R. P., Carranza, J. C., Vallejo, G. A., and Zingales, B. 2000. Amplification of a specific repetitive DNA sequence for Trypanosoma rangeli identification and its potential application in epidemiological investigations. Experimental Parasitology 96, 147– 159. Trypanosoma rangeli can infect humans as well as the same domestic and wild animals and triatomine vectors infected by Trypano soma cruzi in Central and South America. This overlapping distribution complicates the epidemiology of American trypanosomiasis due to the cross-reactivity between T. rangeli and T. cruzi antigens and the pres ence of conserved DNA sequences in these parasites. We have isolated a T. rangeli-specific DNA repetitive element which is represented in approximately 103 copies per parasite genome and is distributed in several chromosomal bands. The 542-bp nucleotide sequence of this element, named P542, was determined and a PCR assay was standard ized for its amplification. The sensitivity of the assay is high, allowing the detection of one tenth of the DNA content of a single parasite. The presence of the P542 element was confirmed in 11 T. rangeli isolates from mammalian hosts and insect vectors originating from several countries in Latin America. Negative amplification was ob served with different T. cruzi strains and other trypanosomatids. The potential field application of the P542 PCR assay was investigated in simulated samples containing T. rangeli and/or T. cruzi and intestinal tract and feces of Rhodnius prolixus. Epidemiological studies were conducted in DNA preparations obtained from the digestive tracts of 12 Rhodnius colombiensis insects collected in a sylvatic area in Colombia. Positive amplification of the P542 element was obtained in 9/12 insects. We have also compared in the same samples the diagnostic performance of two PCR assays for the amplification of the variable domain of minicircle kinetoplast DNA (kDNA) and of the large subunit (LSU) of the ribosomal RNA gene of T. cruzi and T. rangeli. Data indicate that the kDNA PCR assay does not allow diagnosis of mixed infections in most insects. On the other hand, the PCR assay of the LSU RNA gene showed lower sensitivity in the detection of T. rangeli than the PCR assay of the P542 element. It is predicted that the use of sensitive detection techniques will indicate that the actual distribution of T. rangeli in America is wider than presumed.