[Schistosomiasis mansoni in Bahia, Brazil: historical trends and control measures].

In order to aid the development of new approaches to schistosomiasis control, changes were analyzed in prevalence at the county level in the State of Bahia from the 1950s to the 1990s, as were determinants and the effect of community-based chemotherapy. In general, no substantial changes were observed in the basic pattern of spatial distribution of the prevalence of infection. However, during the period studied, there was an overall reduction in prevalence from 15.6% to 9.5% and an increase in prevalence rates in some counties from the western, southeastern, and northern areas of Bahia, indicative of new transmission areas. The effect of mass chemotherapy was analyzed. In the Paraguaçu Basin, where this control measure was used on a large scale, there was a reduction in prevalence similar to areas where this measure was not used. Correlation and regression analysis also failed to show links between mass chemotherapy and long term reduction in prevalence. The most powerful variables to explain these changes were those related with population dynamics. These findings strongly suggest that the reduction in prevalence observed in some areas of the State must be attributed to factors related with the spatial organization of this territory, causing a general decrease in the transmission rate, secondary to mass chemotherapy. At the same time, the incomplete form and the spatial inequalities that characterized the urbanization process created favorable conditions for the spread of schistosomiasis mansoni and the establishment of new foci.