RESUMO
Chagas disease is an endemic zoonosis native to the Americas and is caused by the kinetoplastid protozoan parasite Trypanosoma cruzi. The parasite is also highly genetically diverse, with six discrete typing units (DTUs) reported TcI - TcVI. These DTUs broadly correlate with several epidemiogical, ecological and pathological features of Chagas disease. In this manuscript we report the most comprehensive evaluation to date of the genetic diversity of T. cruzi in Venezuela. The dataset includes 778 samples collected and genotyped over the last twelve years from multiple hosts and vectors, including nine wild and domestic mammalian host species, and seven species of triatomine bug, as well as from human sources. Most isolates (732) can be assigned to the TcI clade (94.1%); 24 to the TcIV group (3.1%) and 22 to TcIII (2.8%). Importantly, among the 95 isolates genotyped from human disease cases, 79% belonged to TcI - a DTU common in the Americas, however, 21% belonged to TcIV- a little known genotype previously thought to be rare in humans. Furthermore, were able to assign multiple oral Chagas diseases cases to TcI in the area around the capital, Caracas. We discuss our findings in the context of T. cruzi DTU distributions elsewhere in the Americas, and evaluate the impact they have on the future of Chagas disease control in Venezuela.
Assuntos
Doença de Chagas/parasitologia , Variação Genética , Filogeografia , Trypanosoma cruzi/classificação , Trypanosoma cruzi/isolamento & purificação , Animais , Análise por Conglomerados , Genótipo , Humanos , Trypanosoma cruzi/genética , VenezuelaRESUMO
Trypanosoma cruzi is an evolutionarily ancient parasitic protozoan endemic to the Americas. Multiple genetic and phenotypic markers indicate that this parasite is highly diverse, with several divergent and discrete major genotypes reported. Infection multiclonality has been observed among numerous metazoan and unicellular endoparasitic species. However, few studies report the complexity of mixed infections within an individual host in any detail or consider their ecological and biological implications. Here we report extraordinary genetic diversity within single reservoir hosts of T. cruzi I using nine polymorphic microsatellite markers across 211 clones from eight mammals from three different sylvatic foci in South America. Forty-nine distinct multilocus genotypes were defined, with as many as 10 isolated from the same host. We discuss our data in the light of previous population genetic studies of this and related parasitic protozoa and contrast high levels of diversity within each host with the precarious nature of T. cruzi contaminative vectorial transmission. Finally, we propose that non-neutral processes could easily account for the diversity we observe and suggest a functional link with survival in the host.
Assuntos
Variação Genética , Mamíferos/parasitologia , Seleção Genética , Trypanosoma cruzi/classificação , Trypanosoma cruzi/genética , Animais , Animais Selvagens/parasitologia , Análise por Conglomerados , Genótipo , Repetições de Microssatélites , América do Sul , Trypanosoma cruzi/isolamento & purificaçãoRESUMO
BACKGROUND: Rhodnius prolixus is the main vector of Chagas disease in Venezuela. Here, domestic infestations of poor quality rural housing have persisted despite four decades of vector control. This is in contrast to the Southern Cone region of South America, where the main vector, Triatoma infestans, has been eliminated over large areas. The repeated colonisation of houses by silvatic populations of R. prolixus potentially explains the control difficulties. However, controversy surrounds the existence of silvatic R. prolixus: it has been suggested that all silvatic populations are in fact Rhodnius robustus, a related species of minor epidemiological importance. Here we investigate, by direct sequencing (mtcytb, D2) and by microsatellite analysis, 1) the identity of silvatic Rhodnius and 2) whether silvatic populations of Rhodnius are isolated from domestic populations. METHODS AND FINDINGS: Direct sequencing confirmed the presence of R. prolixus in palms and that silvatic bugs can colonise houses, with house and palm specimens sharing seven cytb haplotypes. Additionally, mitochondrial introgression was detected between R. robustus and R. prolixus, indicating a previous hybridisation event. The use of ten polymorphic microsatellite loci revealed a lack of genetic structure between silvatic and domestic ecotopes (non-significant F(ST) values), which is indicative of unrestricted gene flow. CONCLUSIONS: Our analyses demonstrate that silvatic R. prolixus presents an unquestionable threat to the control of Chagas disease in Venezuela. The design of improved control strategies is essential for successful long term control and could include modified spraying and surveillance practices, together with housing improvements.
Assuntos
Habitação , Insetos Vetores/fisiologia , Biologia Molecular/métodos , Rhodnius/fisiologia , Animais , Doença de Chagas/epidemiologia , Doença de Chagas/prevenção & controle , Feminino , Insetos Vetores/genética , Insetos Vetores/crescimento & desenvolvimento , Insetos Vetores/parasitologia , Masculino , Repetições de Microssatélites/genética , Rhodnius/genética , Rhodnius/crescimento & desenvolvimento , Rhodnius/parasitologia , Análise de Sequência de DNA , Venezuela/epidemiologiaRESUMO
The phylogeographical structure of the closely related species Rhodnius prolixus and R. robustus is presented based on a 663-base pair (bp) fragment of the mitochondrial cytochrome b gene. Twenty haplotypes were recovered from 84 samples examined, representing 26 populations from seven Latin American countries. The resulting phylogenetic tree is composed of five major reciprocally monophyletic clades, one representing R. prolixus and four representing R. robustus. While R. prolixus is a very homogeneous assemblage, R. robustus has deeper clades and is paraphyletic, with the clade comprising R. robustus from Venezuela (Orinoco region) more closely related to the R. prolixus clade than to the other R. robustus populations from the Amazon region. The R. robustus paraphyly was supported further by the analysis of a nuclear gene (D2 region of the 28S RNA) for a subset of specimens. The data support the view that R. robustus represents a species complex. Levels of sequence divergence between clades within each region are compatible with a Pleistocene origin. Nucleotide diversity (pi) for all R. prolixus populations was extremely low (0.0008), suggesting that this species went through a recent bottleneck, and was subsequently dispersed by man.