Site-specific occupancy and simulated expansion dynamics of a secondary vector of Chagas disease: a three-year follow-up in the Argentine Chaco

GÜRTLER RE.; RODRÍGUEZ-PLANES LI; GASPE MS; ENRIQUEZ GF; GÜRTLER RE.; RODRÍGUEZ-PLANES LI; GASPE MS; ENRIQUEZ GF

Congreso; 66th Annual Meeting of the American Society of Tropical Medicine and Hygiene; 2017

Sylvatic triatomine species may adapt to domestic or peridomestic habitats (domestication) and become relevant for the transmission of Trypanosoma cruzi, the causal agent of Chagas disease. Triatoma sordida occasionally colonized human sleeping quarters in Paraguay, Bolivia and Brazil whereas the few studies conducted in Argentina found sylvatic and peridomestic colonies marginally infected with T. cruzi. Following a 12-year period free of vector control actions, over three years we surveyed site-specific triatomine infestations before and every 4-5 months after a community-wide house spraying with pyrethroids in a well-defined rural area of northern Argentina including 353 houses. Timed-manual searches found 78 of 2177 (peri)domestic sites occupied by T. sordida at baseline, with most (85.9%) insects in chicken nests, chicken coops and chicken trees (suitable habitats). A large fraction of suitable habitats were empty despite their proximity to occupied sites. An incidence function metapopulation model (including distances between sites and maximum local catch across the 3-year period as a proxy of vector carrying capacity) was fitted to the baseline pattern of occupancy. Simulation over 500 time steps predicted a steep increase up to an equilibrium of 250 occupied patches, almost fourfold the observed occupancy. Simulations using R were unable to recover the data fitted by the model, indicating that the observed occupancy pattern represented a transient state (not a quasi-stationary equilibrium) despite the absence of major disturbances (deforestation, insecticide). The prevalence of house infestation with T. sordida decreased from 19.0% at baseline to a minimum (8.1%) at 8 months post-spraying (MPS), and then increased gradually to a mean of 14.2% over 22-32 MPS. Only 1% of T. sordida bugs (mainly invading adults) were collected in human sleeping quarters. Our study shows that T. sordida thrived in peridomestic habitats, and occasionally invaded domestic quarters but failed to colonize them. Its expansion at a mesoscale was likely limited by the instability of peridomestic habitats and its low dispersal ability between them.