CHAGAS-DISEASE IN NORTH-WEST ARGENTINA - RISK OF DOMESTIC REINFESTATION BY TRIATOMA-INFESTANS AFTER A SINGLE COMMUNITY-WIDE APPLICATION OF DELTAMETHRIN

The risk of domestic reinfestation by Triatoma infestans after a singl e community-wide application of delta-methrin (2.5% suspension concent rate at 25 mg active ingredient/m(2)) was studied in Amama, north-west Argentina, where no insecticide spraying had been done by official co ntrol services. The percentage of infested houses fell from 88% before spraying in 1985 to nil during the 6 months after spraying, and there after increased from 5% in 1986 to 96% before a second treatment in 19 92, fitting closely to a logistic model (r(2) = 0.997). Significant ri sk factors associated with domestic reinfestation determined from step wise logistic regression and one-factor analysis were the density of T . infestans in bedrooms just before spraying and the surface structure of indoor walls. Peak densities of bugs in 1988-1989 significantly di ffered between levels of both risk factors. Our study suggests the exi stence of stable determinants of infestation linked to the household w hich, in the absence of effective control measures, would also determi ne the speed of house recolonization and the ensuing bug densities. Pl astering of mud walls before application of insecticides to all domest ic and peridomestic structures is supported by the study.