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

Abstract

BackgroundEstablishing the sources of reinfestation after residual insecticide spraying is crucial for vector elimination programs. Triatoma infestans, traditionally considered to be limited to domestic or peridomestic (abbreviated as D/PD) habitats throughout most of its range, is the target of an elimination program that has achieved limited success in the Gran Chaco region in South America.Methodology/Principal FindingsDuring a two-year period we conducted semi-annual searches for triatomine bugs in every D/PD site and surrounding sylvatic habitats after full-coverage spraying of pyrethroid insecticides of all houses in a well-defined rural area in northwestern Argentina. We found six low-density sylvatic foci with 24 T. infestans in fallen or standing trees located 110–2,300 m from the nearest house or infested D/PD site detected after insecticide spraying, when house infestations were rare. Analysis of two mitochondrial gene fragments of 20 sylvatic specimens confirmed their species identity as T. infestans and showed that their composite haplotypes were the same as or closely related to D/PD haplotypes. Population studies with 10 polymorphic microsatellite loci and wing geometric morphometry consistently indicated the occurrence of unrestricted gene flow between local D/PD and sylvatic populations. Mitochondrial DNA and microsatellite sibship analyses in the most abundant sylvatic colony revealed descendents from five different females. Spatial analysis showed a significant association between two sylvatic foci and the nearest D/PD bug population found before insecticide spraying.ConclusionsOur study shows that, despite of its high degree of domesticity, T. infestans has sylvatic colonies with normal chromatic characters (not melanic morphs) highly connected to D/PD conspecifics in the Argentinean Chaco. Sylvatic habitats may provide a transient or permanent refuge after control interventions, and function as sources for D/PD reinfestation. The occurrence of sylvatic foci of T. infestans in the Gran Chaco may pose additional threats to ongoing vector elimination efforts.

New Sylvatic Hosts of Trypanosoma cruzi and Their Reservoir Competence in the Humid Chaco of Argentina: A Longitudinal Study

“…This process apparently occurred in southern Brazil and included Didelphis opossums and T. sordida. 48 The repeated findings of sylvatic colonies of Triatoma infestans in the Gran Chaco [49][50][51] suggest that domestic or peridomestic parasite or vector spillovers occur.…”

Susceptibility and resistance to deltamethrin of wild and domestic populations of Triatoma infestans (Reduviidae: Triatominae) in Bolivia: new discoveries

“…The flow of insects between sylvatic and domestic habitat is of great importance in vector control because sylvatic populations can be a source of reinfestation of dwellings and are more widespread than was previously thought. Ceballos et al (2011) showed that some T. infestans wild colonies were closely connected to domestic conspecifics in the Argentinean Chaco and that sylvatic habitats may provide a transient or permanent refuge after control interventions, functioning as sources for domestic/peridomestic reinfestation. Given the possible large numbers of wild populations in the dwelling-reinfestation process, it is imperative that we fully understand the origin of the resistance to insecticide observed in wild populations of T. infestans and more accurately measure the flow of insects between wild and domestic foci through further genetic analyses and behavioural studies.…”

“…Moreover, discoveries of sylvatic foci in Argentina, Paraguay and Chile show that sylvatic populations of T. infestans are more widespread than initially described (Ceballos et al 2009, Bacigalupo et al 2010, Rolón et al 2011. It is worth noting that these sylvatic populations have the potential to jeopardise control efforts because of possible free insect movements between the sylvatic environment and dwellings (Noireau et al 2005, Ceballos et al 2011. Because wild populations may recolonise insecticide-treated areas, it is extremely important to know their response to insecticides.…”

Ecological host fitting of Trypanosoma cruzi TcI in Bolivia: mosaic population structure, hybridization and a role for humans in Andean parasite dispersal

“…2010) and to the south in the arid, lowland Chaco region (Ceballos et al . 2011; Waleckx et al . 2012), where their potential for domestic re‐invasion threatens the success of the National Control Programme (Noireau et al .…”