Abstract
BackgroundThe elimination of Triatoma infestans, the main Chagas disease vector in the Gran Chaco region, remains elusive. We implemented an intensified control strategy based on full-coverage pyrethroid spraying, followed by frequent vector surveillance and immediate selective insecticide treatment of detected foci in a well-defined rural area in northeastern Argentina with moderate pyrethroid resistance. We assessed long-term impacts, and identified factors and procedures affecting spray effectiveness.Methods and FindingsAfter initial control interventions, timed-manual searches were performed by skilled personnel in 4,053 sites of 353–411 houses inspected every 4–7 months over a 35-month period. Residual insecticide spraying was less effective than expected throughout the three-year period, mainly because of the occurrence of moderate pyrethroid resistance and the limited effectiveness of selective treatment of infested sites only. After initial interventions, peridomestic infestation prevalence always exceeded domestic infestation, and timed-manual searches consistently outperformed householders' bug detection, except in domiciles. Most of the infestations occurred in houses infested at baseline, and were restricted to four main ecotopes. Houses with an early persistent infestation were spatially aggregated up to a distance of 2.5 km. An Akaike-based multi-model inference approach showed that new site-level infestations increased substantially with the local availability of appropriate refugia for triatomine bugs, and with proximity to the nearest site found infested at one or two preceding surveys.Conclusions and SignificanceCurrent vector control procedures have limited effectiveness in the Gran Chaco. Selective insecticide sprays must include all sites within the infested house compound. The suppression of T. infestans in rural areas with moderate pyrethroid resistance requires increased efforts and appropriate management actions. In addition to careful, systematic insecticide applications, housing improvement and development policies that improve material conditions of rural villagers and reduce habitat suitability for bugs will contribute substantially to sustainable vector and disease control in the Gran Chaco.
Highlights
Field trials carried out in Brazil and Argentina in 1948 demonstrated the effectiveness of hexachlorocyclohexane for suppressing domestic infestations with Triatoma infestans, one of the major vectors of Trypanosoma cruzi [1,2]
Selective insecticide sprays must include all sites within the infested house compound
Decades of vector control actions and screening of blood donors dramatically reduced the numbers of infected people and population at risk; Brazil, Chile and Uruguay were declared free of blood-borne and vector-borne transmission of T. cruzi mediated by T. infestans, and the extent and intensity of infestations were substantially reduced in some sections of Argentina, Bolivia and Paraguay [4,5]
Summary
Field trials carried out in Brazil and Argentina in 1948 demonstrated the effectiveness of hexachlorocyclohexane for suppressing domestic infestations with Triatoma infestans, one of the major vectors of Trypanosoma cruzi [1,2]. Chagas disease vector control programs typically have an initial ‘attack phase’ (in which full-coverage applications of insecticide are made) followed by a ‘surveillance phase’, in which vector detection surveys and selective insecticide sprays are implemented [3]. The major obstacle to attain effective control of the major vectors of Chagas disease using residual insecticide spraying has been the reappearance of triatomine bugs and the difficulties in addressing this recurrent process. We implemented an intensified control strategy based on full-coverage pyrethroid spraying, followed by frequent vector surveillance and immediate selective insecticide treatment of detected foci in a well-defined rural area in northeastern Argentina with moderate pyrethroid resistance. We assessed long-term impacts, and identified factors and procedures affecting spray effectiveness
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