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Chagas disease in the Southern Cone countries

Historically the main vector for the region was T. infestans. However, with the eminent success of the Southern Cone program, having effectively eliminated T. infestans from Brazil, Chile, and Uruguay, and many parts of Argentina, it has been demonstrated that the center of radiation for the species is in Bolivia,99 where it most likely continues to cause a problem due to ready reinvasion from sylvatic foci. Domestic infestations continue to persist in the Chaco region where sylvatic foci of T. infestans are present. Several other species are implicated as secondary vectors, particularly since the control of T. infestans, and the presentation of the niche to other species. In northeastern Brazil, T. brasiliensis and T. psuedomaculata show strong tendencies to colonize domestic habitats along with Panstrongylus megistus in southern Brazil. Other species that have shown some potential to domiciliation are R. neglectus, T. vitticeps, and T. rubrovaria in Brazil. Triatoma sordida is an important secondary vector in Paraguay, Bolivia, northern Argentina, and southern Brazil. T. sordida and a related species, T. guasayana, demonstrate mass dispersal during the dry season, which can result in the invasion of domestic environments.100

T. cruzi subtypes TcII and TcVI predominate in both sylvatic and domestic cycles in this region. Interestingly TcI is also present in many arboreal hosts, such as Didelphis species. The absence of Rhodnius species in the southern part of this region and the lack of data for other triatomines carrying TcI present the possibility that transmission of TcI, in Didelphis at least, commonly occurs without vectors by direct contamination from the anal scent glands.101 However, P. megistus has been implicated with TcI transmission in southern central Brazil,102 as has as a species of Rhodnius, R. neglectus,1103 which has a distribution extending from the Amazon to southern Brazil. Also, Triatoma (Mepraia) spinolai in Chile has been reported to be infected with TcI.104 Other vector species may yet to be implicated in TcI transmission because it is often difficult to sample from sylvatic habitats directly. Table 5.2 summarizes the actions and strategies to be taken for controlling triato- mine species in the different initiatives in the Americas.

Tabie 5.2 Action to be taken for controlling autoctonous or introduced triatomine species in different control initiatives in the Americasa

Region

Perspectives

Southern countries and Southern Peru

Introduced triatomine species present a high degree of domiciliation (i.e., Triatoma infestans) and are vulnerable to latest generation insecticide action and can thus be eliminated, as has been demonstrated in Brazil, Chile and Uruguay. It is totally feasible that the other countries involved in the Southern Cone and Southern initiative can achieve this goal in the short- and medium-term. Autochthonous species (such as Triatoma brasiliensis, Panstrongylus megistus, and Triatoma sordida) require an ongoing entomological surveillance given that they can adapt to human habitat

Andean and Central-American countries' initiatives

Introduced triatomine species presenting a high degree of domiciliation (such as Rhodnius prolixus) in extensive areas of Colombia, Venezuela, and in most Central America countries (except for El Salvador and Panama), the same as Rhodnius ecuadoriensis in Ecuador and Northern Peru, are vulnerable to insecticide action and can thus be eliminated as has been demonstrate with R. prolixus in some regions of Guatemala and Venezuela. Peridomiciliated species

(Continued)

Table 5.2 (Continued)

Region

Perspectives

(such as Triatoma dimidiata) require the physical management of human habitations and the peridomiciliary environment, as well as sustained entomological surveillance programmes. Some species from sylvatic habitats represent a challenge for future control action, as in the case of silvatic R. prolixus populations in Venezuela and Colombia

Amazonian countries' initiatives

The Amazonian initiative for vectorial control of Chagas' disease is formed by nine South American countries, representing an important challenge in terms of entomological surveillance and merits special attention in the immediate future. Different Rhodnius and Panstrongylus species present in the Amazon Region must be considered to be epidemiologically important potential vectors

All continental initiatives

It must be born in mind that, in spite of the

achievements made in different regional initiatives, Chagas disease persist in Latin America given that it represents a silvatic enzooty and anthropozoonosis and therefore requires long-term surveillance and control action

 
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