The Pampa del Indio project: District-wide quasi-elimination of Triatoma infestans after a 9-year intervention program in the Argentine Chaco.

Background: The elimination of Triatoma infestans, the main domestic vector of Trypanosoma cruzi, is lagging behind expectations in the Gran Chaco region. We implemented an insecticide-based intervention program and assessed its long-term effects on house infestation and bug abundance in a resource-constrained municipality (Pampa del Indio, northeastern Argentina) inhabited by creole and the Qom indigenous people (2007–2016). Key questions were whether district-wide data integration revealed patterns concealed at lower spatial levels; to what extent preintervention infestation and pyrethroid resistance challenged the effectiveness of insecticide-based control efforts, and how much control effort was needed to meet defined targets. Methods: Supervised vector control teams i) georeferenced every housing unit at baseline (1,546); ii) evaluated house infestation using timed-manual searches with a dislodging aerosol across four rural areas designated for district-wide scaling up; iii) sprayed with pyrethroid insecticide 92.7% of all houses; iv) periodically monitored infestation and promoted householder-based surveillance, and v) selectively sprayed the infested houses, totaling 1,823 insecticide treatments throughout the program. Results: Baseline house infestation (mean, 26.8%; range, 14.4–41.4%) and bug abundance plummeted over the first year postintervention (YPI). Timed searches at baseline detected 61.4–88.0% of apparent infestations revealed by any of the methods used. Housing dynamics varied widely among areas and between Qom and creole households. Preintervention triatomine abundance and the cumulative frequency of insecticide treatments were spatially aggregated in three large clusters overlapping with pyrethroid resistance, which ranged from susceptible to high. Persistent foci were suppressed with malathion. Aggregation occurred mainly at house compound or village levels. Preintervention domestic infestation and abundance were much greater in Qom than in creole households, whereas the reverse was recorded in peridomestic habitats. House infestation, rare (1.9–3.7%) over 2–6 YPI, averaged 0.66% (95% confidence interval, 0.28–1.29%) at endpoint. Conclusions: Upscale integration revealed multiple coupled heterogeneities (spatial, sociodemographic and biological) that reflect large inequalities, hamper control efforts, and provide opportunities for targeted, sustainable disease control. High-coverage, professional insecticide spraying combined with systematic surveillance-and-response were essential ingredients to achieve the quasi-elimination of T. infestans within 5 YPI and concomitant transmission blockage despite various structural threats and constraints. Author summary: The Gran Chaco ecoregion is the main hotspot of Chagas disease. We assessed the district-wide effects of an insecticide-based intervention program on house infestation with the main vector Triatoma infestans in rural villages of Pampa del Indio municipality, in the Argentine Chaco. The program included periodic assessments of house infestation and household demographics; blanket house spraying with pyrethroid insecticide at the outset; promotion of householder-based surveillance, and systematic vector surveillance-and-response over a 9-year period. We found that house infestation plummeted over the first year postintervention (YPI); became rare over 2–6 YPI, and fell below 1% at endpoint. House infestation was spatially aggregated in three large clusters that partially overlapped with pyrethroid resistance. Triatomine aggregation occurred mainly at house compound or village levels. Indigenous households were at much greater risk of vector-borne transmission than creole households. We conclude that gradual scaling up of high-coverage, professional insecticide spraying combined with systematic surveillance-and-response operations within an adaptive management framework can achieve the quasi-elimination of T. infestans and concomitant blockage of vector-borne transmission in resource-constrained, remote rural settings. [ABSTRACT FROM AUTHOR]