Genetics and evolution of triatomines: from phylogeny to vector control

Abstract

Triatomines are hemipteran bugs acting as vectors of the protozoan parasite Trypanosoma cruzi. This parasite causes Chagas disease, one of the major parasitic diseases in the Americas. Studies of triatomine genetics and evolution have been particularly useful in the design of rational vector control strategies, and are reviewed here. The phylogeography of several triatomine species is now slowly emerging, and the struggle to reconcile the phenotypic, phylogenetic, ecological and epidemiological species concepts makes for a very dynamic field. Population genetic studies using different markers indicate a wide range of population structures, depending on the triatomine species, ranging from highly fragmented to mobile, interbreeding populations. Triatomines transmit T. cruzi in the context of complex interactions between the insect vectors, their bacterial symbionts and the parasites; however, an integrated view of the significance of these interactions in triatomine biology, evolution and in disease transmission is still lacking. The development of novel genetic markers, together with the ongoing sequencing of the Rhodnius prolixus genome and more integrative studies, will provide key tools to expanding our understanding of these important insect vectors and allow the design of improved vector control strategies.

Figure 1

Distribution of triatomine species of major epidemiological relevance. Only about 20 triatomine species are responsible for T. cruzi transmission to humans, because of their ability to infest and, for some species, to colonize human habitat. The red areas indicate the approximate species geographic distribution. Species highlighted in red are considered the most important vectors of the parasite.

Figure 2

T. cruzi life cycle. Following a blood meal containing bloodstream trypomastigotes, T. cruzi parasites first differentiate into the epimastigote stage and multiply asexually, before differentiating into infectious metacyclic trypomastigotes. Upon entry of trypomastigotes in the mammalian host, those are able to invade cells and further replicate as intracellular amastigotes (from Andrade and Andrews, 2005, with permission).

Figure 3

Interaction network. Triatoma, Trypanosoma and microorganisms (either symbiotic or not) interact with one another. Direct or indirect interactions, which have been documented in this review, are all included in this figure. The question marks indicate interactions, which have not yet been investigated.

Figure 4

Innovative vector control interventions. Novel interventions, based on detailed knowledge of triatomine species population dynamics and genetics, may rely on improving wall plastering of houses using traditional methods, which prevents colonization (a), or on the installation of insect screens on windows, to prevent transient infestation (b).