Slow recovery rates and spatial aggregation of Triatoma infestans populations in an area with high pyrethroid resistance in the Argentine Chaco

Abstract

Background The emergence of pyrethroid resistance has threatened the elimination of Triatoma infestansfrom the Gran Chaco ecoregion. We investigated the status and spatial distribution of house infestation with T.infestans and its main determinants in Castelli, a municipality of the Argentine Chaco with record levels of triatominepyrethroid resistance, persistent infestation over 2005–2014, and limited or no control actions over 2015–2020.Methods We conducted a 2-year longitudinal survey to assess triatomine infestation by timed manual searchesin a well-defined rural section of Castelli including 14 villages and 234 inhabited houses in 2018 (baseline) and 2020,collected housing and sociodemographic data by on-site inspection and a tailored questionnaire, and synthetizedthese data into three indices generated by multiple correspondence analysis.Results The overall prevalence of house infestation in 2018 (33.8%) and 2020 (31.6%) virtually matched the historicalestimates for the period 2005–2014 (33.7%) under recurrent pyrethroid sprays. While mean peridomestic infestationremained the same (26.4–26.7%) between 2018 and 2020, domestic infestation slightly decreased from 12.2 to 8.3%.Key triatomine habitats were storerooms, domiciles, kitchens, and structures occupied by chickens. Local spatialanalysis showed significant aggregation of infestation and bug abundance in five villages, four of which had very highpyrethroid resistance approximately over 2010–2013, suggesting persistent infestations over space-time. House bugabundance within the hotspots consistently exceeded the estimates recorded in other villages. Multiple regressionanalysis revealed that the presence and relative abundance of T. infestans in domiciles were strongly and negativelyassociated with indices for household preventive practices (pesticide use) and housing quality. Questionnaire-derivedinformation showed extensive use of pyrethroids associated with livestock raising and concomitant spillover treatmentof dogs and (peri) domestic premises.Conclusions Triatoma infestans populations in an area with high pyrethroid resistance showed slow recoveryand propagation rates despite limited or marginal control actions over a 5-year period. Consistent with these patterns,independent experiments confirmed the lower fitness of pyrethroid-resistant triatomines in Castelli compared.