Genetic diversity of Triatoma infestans (Hemiptera: Reduviidae) in Chuquisaca, Bolivia based on the mitochondrial cytochrome b gene

Abstract

(Pless et al. 1992, Wincker et al. 1997, Brenière et al. 2002.Control of the parasite is hampered by the complex ecology of its transmission. T. cruzi has multiple mammalian hosts and insect vectors. Non-human mammal hosts include dogs, domestic and wild guinea pigs and various peri-domestic animals such as goats, sheep, and pigs. Vector populations, with the potential for transmission, can be found in domestic environments, where they feed on dogs and guinea pigs kept in homes, in peri-domestic homestead associations, and in sylvatic zones associated with wild guinea pigs. In Argentina, Brazil, Chile, and Uruguay, T. infestans is exclusively domestic or peri-domestic, thus eradication of the vector in these habitats, followed by vigilance against re-infestation, has proven largely successful in reducing transmission of T. cruzi and thus the prevalence of Chagas disease. In contrast, in Bolivia the vectors occur in domestic, peri-domestic, and sylvatic environments. Thus, control of T. infestans in towns and homesteads is confounded by the possible re-infestation from surrounding sylvatic areas. In addition, recent work in peridomestic sites in Argentiana has shown that spraying with pyrethroids does not always eradicate T. infestans and that infestations present a year after spraying resulted from individuals that had survived treatment (Gürtler et al. 2003). Audino et al. (2004) have shown that higher activities of degradative esterases and P450 contribute to deltamethrin resistance.It has been suggested that the Cochabamba valley, to the north of Chuquisaca, is the geographic origin and epicenter of spread of T. infestans (Torrico 1946, Schofield 1988. However, Dujardin et al. (1998) sampled from the Sucre region of Chuquisaca using allozymes, and in a comparison with other Andean and non-Andean regions determined that the Sucre-Vallegrande-Potosi area is the center of origin and dispersion of T. infestans. We conducted a study over a larger area within Chuquisaca using a fragment of the mitochondrial cytochrome b gene, as in Monteiro et al. (1999), for 62 specimens from periurban and rural localities in order to ascertain the population structure of T. infestans in this region and determine whether cyt b is a useful marker for this purpose.Evolutionary theory predicts higher genetic variation in ancestral sylvatic populations than in recently derived domestic populations, and in domestic populations that intermix with sylvatic populations (Schofield & Dias 1999). If the Cochabamba Valley, the neighboring Department of Chuquisaca or both are the geographic origin and epicenter of spread of T. infestans, insects collected in these regions should display more genetic variation. On the other hand, populations of T. infestans, which are highly adapted to domestic environment may show less genetic variation as a result of human dissemination.

Wild Triatoma infestans, a potential threat that needs to be monitored

“…The results showed high genetic variability: seven haplotypes were identified in 38 triatomines analysed (P Kengne & F Noireau, unpublished observations). Among the sylvatic haplotypes, two of them were also found in domestic insects from the Sucre Region (Giordano et al 2005). The detection of seven haplotypes in wild T. infestans from a limited area supports the evolutionary theory, which predicts higher genetic variability in the ancestral wild populations than in their domestic derivatives .…”

“…However, recent findings based on allozymes, genome size and nuclear rDNA favour the Andean hypothesis (Dujardin et al 1998, Panzera et al 2004, Bargues et al 2006). This would imply that the dark morph populations, which exhibit an important reduction of heterochromatin and DNA amounts as well as a considerable degree of genetic isolation, represent a direct expansion from the Andean populations (Monteiro et al 1999, Giordano et al 2005). However, the occurrence of at least one recolonisation of a sylvatic habitat from a domestic population in the Chaco was not discarded (Panzera et al 2004, Bargues et al 2006.…”

“…Most studies were based on allozymes and reported low polymorphism as inferred from results on two or three polymorphic loci (Pereira et al 1996, Dujardin et al 1998. Recent studies based on mitochondrial or nuclear gene sequences from domestic populations detected higher levels of genetic variation than expected (Giordano et al 2005, Bargues et al 2006). To assess the genetic variability in a wild T. infestans population, a mitochondrial cytochrome b (Cytb) gene fragment was sequenced in insects sampled from a very small area (< 1 km 2 ) in the Cochabamba valley, at 2,700 m asl.…”

Genetics and evolution of triatomines: from phylogeny to vector control

“…sequence (Giordano et al, 2005)). This hypothesis is supported by cytogenetic differences in the Andean as compared with non-Andean T. infestans, DNA sequence differences (ITS-2 (Bargues et al, 2006) and cytb (Monteiro et al, 1999 andGiordano et al, 2005)), as well as a highly significant F ST ¼0.36 between populations from the two areas (based on cytb (Giordano et al, 2005)).…”

Temporal differences in blood meal detection from the midguts of Triatoma infestans

“…In a sylvatic environment, wild animals act as main blood meal sources; risk of T. cruzi transmission to people is limited due to fewer encounters between infected vectors and humans. In the case of T. infestans, the peridomestic and domestic blood meal sources have included domestic dogs, chickens, goats, pigs, cows, domesticated guinea pigs, and humans 6,7,15,16,17,21 . In domestic and peridomestic sites, vectors are more likely to feed on humans.…”