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

Abstract

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.

Domestic (re)infestation risk with the main vector Triatoma infestans increases with surrounding green vegetation and social vulnerability in the Argentine Chaco

“…These models identified two main regions with infestation risk not explained by the sociodemographic and environmental variables included in the fixed-effects models. The main region with the largest size and a positive risk of domestic infestation across both intervention periods occurred in Area I [ 22 ], where house infestation over the first 3 years postintervention was strongly associated with mud walls, thatched roofs, high refuge availability for triatomines, domestic host abundance and lack of domestic use of insecticides [ 25 ]. Area I displayed the highest prevalence of preintervention house infestation (41.4%) and required proportionally more house sprays with pyrethroid insecticide than the rest of the municipality [ 22 ].…”

“…The municipality extends over approximately 60 km by 30 km and includes two loosely connected urban centers (Pampa del Indio and Pueblo Viejo), a peri-urban section (Parque Industrial) and 32 dispersed rural settlements. The rural section of the municipality was divided into four areas (I, II, II and IV) for operational purposes [ 22 ]. Based on a supervised classification, Rodríguez-Planes [ 30 ] showed that in Pampa del Indio the estimated percentage of land covered by different types of forests (with different degrees of degradation) was 74.4% and 72.4% in December 2006 and August 2015, respectively.…”

“…A house was considered infested if any live nymph or adult was found (excluding eggs). House infestation prevalence was 26.8% (range: 14.4–41.4%) in the preintervention period; it was rare (range: 1.9–3.7%) over 2–6 years postintervention and dropped to 0.7% (95% confidence interval, 0.28–1.29%) at endpoint across rural areas [ 22 ].…”

“…This study is part of an ongoing research and control program on the eco-epidemiology of Chagas disease in the municipality of Pampa del Indio (Chaco province, Argentina) initiated in 2007. A series of district-wide interventions achieved the quasi-elimination of T. infestans [ 22 ] and the virtual interruption of vector-borne transmission of T. cruzi at the municipality-wide level [ 23 , 24 ]. House infestation in operational areas within Pampa del Indio was associated with residential overcrowding, household educational level, Qom ethnicity, domestic insecticide use and mud walls [ 7 , 25 , 26 ].…”

Human Trypanosoma cruzi infection in the Argentinean Chaco: risk factors and identification of households with infected children for treatment

“…Several studies have identified risk factors of human infection with T. cruzi at different levels: individual, household, social group or community, and landscape or region [ 23 – 31 ]. In general, duration of exposure, the presence and abundance of infected triatomines in domiciles, building materials of walls and roof, and presence and number of infected dogs and cats and of other infected human residents in the household (i.e.…”