The Environmental Science of Drinking Water

by Triatoma infestans after insecticide spraying has caused elimination efforts in the dry Chaco region to fail repeatedly. The sources and spatial extent that need to be considered to understand the reinfestation pattern and to plan a comprehensive control program were studied in 2 adjacent rural communities in northwestern Argentina from 1993 to 1997. The effects of external, residual , and primary sources on the reinfestation pattern were evaluated by using geographic information systems, satellite imagery, spatial statistics, and 5-year retrospective data for 1,881 sites. The reinfestation process depended on primary internal sources and on surrounding infested communities. In the dry Chaco, successfully reducing the risk for reinfestation in a community depends on treating all communities and isolated sites within 1,500 m of the target community. In addition, during the surveillance phase, spraying all sites within 500 m of new foci will delay reinfes-tation. T riatoma infestans, the main domestic vector of Chagas disease in Latin America, can disperse actively by flying or walking and passively through accidental carriage on humans and their belongings (1,2). Based mostly on the residual application of pyrethroid insecticides (3), an ongoing regional T. infestans elimination program has achieved only limited results in the dry Chaco region because of repeated reinfestation. Sources for reinfestation may be residual foci where triatomine bugs survived exposure to insecticides, preexisting foci overlooked by vector control staff, and adjacent infested communities left untreated (4–7). In northwestern Argentina and Bolivia, peridomestic foci of T. infestans detected just 1–3 months after applying pyrethroids were most probably residual foci (5,8–10). In the apparent absence of sylvatic foci of T. infestans in northern Argentina (11), the appearance of adult T. infestans can be explained by active dispersal from foci located in its flight distance (12–14). This flight distance is well within the range of clustering detected around external (up to 1,500 m) and internal sources (up to 400 m) observed in an earlier study (7). Using geographic information systems, satellite imagery, spatial statistics, and retrospective data collected over 5 years, we identified T. infestans sources after community wide insecticide spraying in an isolated rural community , Amamá, in northwestern Argentina (7). One year after spraying, an initial peridomestic focus was detected, and subsequent infestations clustered around it. This clustering suggested that residual spraying with insecticides in the colonized site and all sites in a radius of 450 m is necessary to prevent subsequent propagation …