Chagas disease vector control in Tupiza, Southern Bolivia

RESUMO

Heavy domestic and peridomestic infestations of Triatoma infestans were controlled in two villages in southern Bolivia by the application of deltramethrin SC25 (2,5 per cent suspension concentrate) at a target dose of 25 mg a.i.m². Actual applied dose was monitored by HPLC analysis of filter papers placed at various heights on the house walls, and was shown to range from 0 to 59.6 about a mean of 28.5 mg a.i./m². Wall bioassays showed high mortality of T.infestans during the first month after the application of deltamethrin. Mortality declined to zero as summer temperatures increased, but reappeared with the onset of the following winter. In contrast, knockdown was apparent throughtout the trial, showing no discernible temperature dependence. House infestation rates, measured by manual sampling and use of paper sheets to collect bug faeces, declined from 79 per cent at the beginning of the trial to zero at the 6 month evalution. All but one of the houses were still free of T.infestans at the final evaluation 12 months after spraying, although a small number of bugs were found at this time in 5 of 355 peridomestic dependencies. Comparative cist studies endorse the recommendation of large-scale application of deltamethrin or pyrethroid of similar cost-effectiveness, as a means to eliminate domestic T.infestans populations in order to interrupt transmission of Chagas disease.