The Pampa del Indio Project: long-term variations of Trypanosoma cruzi infection in Triatoma sordida, a non-target invasive vector

Introduction The Gran Chaco region still faces vector-borne transmission of Trypanosoma cruzi by the main vector, Triatoma infestans . In Pampa del Indio, a municipality belonging to the Argentinian Chaco, a long-term research and intervention program achieved the quasielimination of T. infestans from rural houses and halted the domestic vector-borne transmission of T. cruzi . Here, we evaluate the occurrence and distribution of T. cruzi infection in Triatoma sordida sensu lato , a secondary species that frequently invades rural domiciles and colonizes the peridomestic environment, over 2007-2016. Based on the prevalence of infection reported across the Gran Chaco region in the absence of T. infestans and given the limited sensitivity of optical microscopy, we hypothesized that T. cruzi infection in T. sordida post-intervention would be higher than in our previous reports (0-6%). Methods and results Of 10,728 T. sordida collected at 528 premises along the intervention, we examined 1,946 specimens by OM or vkDNA-PCR and found a naïve prevalence of T. cruzi infection of 1.44% (95% CI: 0.10% –2.07%). The mean number of infected T. sordida per house was 1.12 (SD = 0.33). Infection was higher in adults rather than nymphs; maximal in domiciles, intermediate in peridomestic kitchens, storerooms and granaries, and minimal in other peridomestic sites. Spatial analysis identified an infection hotspot in the northwestern section of the municipality. By means of single-season occupancy models, we estimated that the detection probability of T. cruzi infection was method-dependent, with OM detecting at most 73% of the truly infected T. sordida (assuming 100% detectability with vkDNA-PCR). Across nearly a decade of vector surveillance and control, T. cruzi infection in T. sordida remained <2%, and ≤5% of the houses harboring T. sordida exhibited infected specimens. Discussion We report relatively low levels of T. cruzi infection, one component of Chagas disease transmission risk, in the currently most abundant triatomine vector in Pampa del Indio. Given the enzootic nature of T. cruzi transmission cycles, our imperfect knowledge on how they function, and the finding of infected T. sordida throughout the post-intervention phase, sustained surveillance within an adaptive management scheme is needed to guarantee long-term vector-borne transmission control.