| Popis: |
Control campaigns against Triatoma infestans, the principal vector of Trypanosoma cruzi, have relied on the application of residual insecticides and have regarded the system as homogeneous. Reinfestation generally starts in peri-domestic residual foci or in preexisting foci that escaped spraying for diverse reasons. From these foci T. infestans adults actively invade other sites, or they are transported passively within objects or goods from infested communities. In the absence of additional spraying of insecticides after the attack phase, domiciliary reinfestation expanded exponentially to return to pre-spraying levels in 3-4 years in Amamá, Santiago del Estero. However, the rate of recovery of T. infestans abundance was much lower than that predicted by a simple mathematical model or in experimental field studies. Reinfestation did not progress homogeneously within the village. Two longitudinal studies in Santiago del Estero revealed that the presence of T. infestans-infested peri-domestic sites increased the risk of domiciliary reinfestation. "Key" sites where reinfestation started early were goat or sheep corrals, pig corrals, chicken houses, and store-rooms. Peri-domestic reinfestation is likely the result of multiple factors, such as insecticide breakdown by climatic agents, and the greater surface and availability of refuge and hosts in peri-domestic rather than domiciliary sites. Such environmental heterogeneity generates insecticidal effects heterogeneity and increases the probability of persistence of T. infestans even under control pressures. Several studies showed that sustained surveillance after the attack phase decreased sharply the domiciliary colonization by T. infestans and the percentage of bugs infected with T. cruzi, and the local incidence of infected children. The sustained elimination of T. infestans demands a scientific approach that is not only centered in insecticide use but that also includes the environment and house-holders in their specific social and political scenario. |
