Infestation of S. Paulo State, Brazil, by Aedes aegypti and Aedes albopictus

Objective To study the influence of the distance between infested and non-infested ar eas in the geographical spread of Aedes aegypti and Aedes albopictus popula tions in the state of S. Paulo. Regional patterns were also studied conside ring the determinants related to soil occupation. Methods Information related to the counties in the state of S . Paula where were co ncentrations of Ae. aegypti and Ae. albopictus and counties infested up to the end of each year (1985 to 1995), both in the stare of S. Paulo and in t he neighboring states, were used. Four indicators were defined to analyze t he infestation process. Results/Conclusions The analysis indicated the contribution of the states of Mato Grosso do Sul and Parana for the initial Ae. aegypti infestation in the state of S. Paul o and Ae. albopictus infestation in the states of Rio de Janeiro and Minas Gerais. In the counties where there was a concentration of these species, t heir establishment was more frequent among those closer to the infested are a. Seventy-five percent of the counties where there were established popula tions of Ae. aegypti and Ae. albopictus were situated up to 34 km and 60 km , respectively from the nearest infested county. The analysis of the geogra phical spread rate of the Ae. aegypti revealed three different large areas with unexpected patterns: the area with greater demographic population dens ity (least of the state) had the lower rate of geographical mosquito spread , indicating the existence of other factors with preponderant influence on the macro-regional patterns. For Ae. albopictus, there was no evidence of a relationship between their geographical spread patterns and the demographi c population density.