Microsatellites Reveal a High Population Structure in Triatoma infestans from Chuquisaca, Bolivia

Chagas disease is a protozoan infection caused by the parasite Trypanosoma cruzi. Chagas is prevalent throughout Central and South America, and it remains a chief concern in Bolivia. A movement that began in 1991 called the Southern Cone Initiative has been successful in reducing the incidence of Chagas disease in the Southern Cone countries of Argentina, Brazil, Chile, and Uruguay; but due to socio-economic and other factors, incidence remains high in Bolivia. The most important mode of transmission of T. cruzi to humans and other mammals is through feces of triatomine bugs. Thus, disease control and transmission prevention focus on elimination of triatomine vectors, and more specifically in Bolivia, it focuses on the elimination of Triatoma infestans. This study focuses on T. infestans in the Department of Chuquisaca, Bolivia. Ten highly variable microsatellite markers were used to analyze the population structure of insects collected in different towns. Statistical analyses show that T. infestans are highly structured, which means that they colonize on a small geographic scale. The results also suggest little active dispersal. These findings should be implemented during control efforts so that insecticide spraying focuses on geographic areas of colonization and re-colonization

Hidden Sylvatic Foci of the Main Vector of Chagas Disease Triatoma infestans: Threats to the Vector Elimination Campaign?

Triatoma infestans, a highly domesticated species and historically the main vector of Trypanosoma cruzi, is the target of an insecticide-based elimination program in the southern cone countries of South America since 1991. Only limited success has been achieved in the Gran Chaco region due to repeated reinfestations. We conducted full-coverage spraying of pyrethroid insecticides of all houses in a well-defined rural area in northwestern Argentina, followed by intense monitoring of house reinfestation and searches for triatomine bugs in sylvatic habitats during the next two years, to establish the putative sources of new bug colonies. We found low-density sylvatic foci of T. infestans in trees located within the species' flight range from the nearest infested house detected before control interventions. Using multiple methods (fine-resolution satellite imagery, geographic information systems, spatial statistics, genetic markers and wing geometric morphometry), we corroborated the species identity of the sylvatic bugs as T. infestans and found they were indistinguishable from or closely related to local domestic or peridomestic bug populations. Two sylvatic foci were spatially associated to the nearest peridomestic bug populations found before interventions. Sylvatic habitats harbor hidden foci of T. infestans that may represent a threat to vector suppression attempts

Temporal variations of wing size and shape of Triatoma infestans (Hemiptera : Reduviidae) populations from Northwestern Argentina using geometric morphometry

Wing geometric morphometry of Triatoma infestans (Klug) (Hemiptera: Reduviidae) populations in northwestern Argentina showed that individual collection sites represent the discrete unit where metric differentiation took place. Here we Studied temporal variations in wing size and shape of T. infestans Populations from defined capture sites on three occasions between 2000 and 2003. Bugs collected front domiciles and/or storerooms had significantly larger right-wing centroid size than bugs collected at goat and/or pig corrals by the end of summer 2000 for both sexes. Conversely, male bugs collected front domiciles and/or storerooms had significantly smaller centroid size than bugs collected from pig corrals in spring 2002. The inversion in wing centroid size between seasons was consistent between sexes. Wing shape analysis from the south-central extreme of the Study village showed divergence between collection dates for both sexes. Wing shape divergence was highly significant between male bugs collected by the end of summer 2000 and those collected in spring 2002 and by the end of summer 2003. For females, wing shape divergence was marginally significant between the end Of Summer 2000 and spring 2002, and significant between spring 2002 and the end of summer 2003. Unlike season-related variations in wing centroid size, shape differentiation wits related to the time period elapsed between sample collections and Suggested genetic influences acting on shape. Simultaneous consideration of wing size and shape provided complementary information on the direction and timing of bug dispersal. Morphological studies may allow determining the degree of relatedness of different bug populations and to associate morphological heterogeneity with temporal patterns of reinfestation

Microgeographic spatial structuring of Triatoma infestans (Hemiptera : Reduviidae) populations using wing geometric morphometry in the Argentine Chaco

We investigated the occurrence of spatial structuring in Triatoma infestans (Klug) (Hemiptera: Reduviidae) populations 12 yr after the last community-wide insecticide spraying campaign in rural Pampa del Indio, in the Gran Chaco of northeastern Argentina. In total, 172 male and 149 female right wings collected at 16 georeferenced sites with at least 10 individuals of the same sex were analyzed using geometric morphometry. Mean female body length and wing centroid size (CS) were significantly larger than for males. Log-transformed CS and length were significantly and positively correlated both for males and females. Males collected in domiciles had significantly smaller CS than those collected in peridomestic structures both closed (kitchens or storerooms) or open (chicken coops), in agreement with our previous results elsewhere in the dry Argentine Chaco. Female wing CS was not significantly different between ecotopes. Wing shape analyses showed the occurrence of significant geographic structuring in males and females combined and in males only. Male wings showed a strong association between Mahalanobis distance and geographic distance. In general, Mahalanobis distances were significantly different between collection sites located >4 km apart. For collection sites located <4 km apart, the greater the geographic distance the larger the difference in wing shape variables. Among females, only a partial correspondence between geographic groups and Mahalanobis distances was recorded. The strong spatial structuring found in T. infestans populations may be useful for the identification of putative reinfestation sources after vector control interventions