Chagas disease, caused by the protozoan Trypanosoma cruzi and transmitted by triatomine insect vectors, affects about 10 million people worldwide (Schmunis 2000) and is the third most important global parasitic disease after malaria and schistosomiasis (World Bank 1993). Because of effective vector control campaigns, the number of acute cases has decreased markedly and has been reduced to nearly zero in previously highly endemic areas of Uruguay, Chile and Brazil (Schofield et al. 2006).The Chagas disease vector Triatoma infestans (Klug 1834) was historically considered an e�clusively do-) was historically considered an e�clusively domestic insect, but it has now been reported in sylvan environments (Noireau et al. 2005, Noireau 2009). The first sylvatic population of T. infestans was reported in Cochabamba, Bolivia, inhabiting rock piles associated with wild guinea pigs (Torrico 1946). Other reports have shown T. infestans in Argentina (Mazza & Schreiber 1938, Mazza 1943, Ceballos et al. 2009), Paraguay (Velasquez & González 1959 and Brazil (Barretto et al. 1963) under rocks or trunks of fallen trees, in hollow trees, under bark, in shelters or burrows of marsupials and rodents and in bird nests occupied by owls, parrots or small rodents (Noireau et al. 1997). Wild T. infestans has been found in an e�tended geographical region throughout Chaco and three Andean departments of Bolivia: Cochabamba, La Paz and Potosí (Noireau et al. 1999, Cortez et al. 2007. T. infestans was considered to be eradicable due to its strictly domestic behavior and its non-autochthonous status outside of its apparent centre of origin in the Andean valleys of Bolivia. This theory has been challenged by empirical evidence of wild individuals collected by vector control programs and researchers over several decades (Gürtler 2009). Sylvatic triatomines may occasionally invade human residences, acting as founders of new colonies (Fitzpatrick et al. 2008). Hence, it is necessary to study the ecology and behavior of their populations to understand the domiciliation process and generate new strategies for their control (Beard et al. 2002, Guhl et al. 2009, Moncayo & Silveira 2009).In Chile, parasite transmission from vectors to humans occurs mainly in rural and suburban areas encompassing the northern desert and semiarid and Mediterranean environments, between latitudes 18°30'S and 34°36'S. The triatomine insects T. infestans, Mepraia spinolai (Porter 1934) and Mepraia gajardoi are the vector species that have been reported in that area (Spinola 1852, Neghme 1982, Lent et al. 1994, Frias et al. 1998.In 1991, several countries of South America, including Chile, established the Southern Cone Initiative for control of Chagas disease (INCOSUR-Chagas), which provided united strategy, control actions and an information system used to evaluate local control programs (Silveira 2002). The specific aims of the initiative were the following: (i) the elimination of T. infestans from dwellings and their surroundings in endemic areas, (ii) the reduction an...

Abstract. In Chile, the main vector of Chagas disease, Triatoma infestans, is under control after insecticide spraying. However, it has been found colonizing wild habitats. This study evaluated Trypanosoma cruzi infection of sylvatic and domiciliary T. infestans and identified their parasite genotypes. The sample studied was composed mainly of T. infestans sylvatic nymphs and domiciliary adults from a semi-urban area with human dwellings under vector control surveillance. Results showed prevalences of 57.7% in nymphs and 68.6% in adults. Hybridization tests showed a major T. cruzi lineage (TcI) circulating in sylvatic (93.3%) and domiciliary (100%) T. infestans. TcII, TcV, and TcVI were also detected, mainly in nymphs, suggesting differential adaptation of T. cruzi lineages among instars. We also discuss the origin of domiciliary individuals of T. infestans and the risk of human infection by triatomines of sylvatic foci that invade houses despite vector control programs.