Ecological Aspects of Biomphalaria in Endemic Areas for Schistosomiasis in Brazil

Schistosomiasis is a disease caused by trematodes belonging to family Schistosomatidae. Within this family, only genus Schistosoma has species that parasitize humans. It is accepted that the genus Schistosoma was brought to the Americas during the Atlantic slave trade and with Eastern and Asian immigrants. However, only Schistosoma mansoni Sambon, 1907, settled here certainly due to the presence of susceptible intermediate hosts, freshwater planorbid snails belonging to the genus Biomphalaria and to environmental conditions similar to the region of origin (Morgan et al., 2001). Of the major endemic diseases that occur in Brazil, schistosomiasis is widely distributed, being considered as a serious medical and socio-economic problem. Brazil is considered one of the endemic foci of the disease, with active transmission in at least 16 states, despite the variability of data regarding its prevalence in different regions of the country (Cunha, 1970; Katz & Peixoto, 2000). Since human activity plays a significant role in expanding the territory colonized by hosts of S. mansoni, human migration has contributed to the expansion of schistosomiasis to developing regions. In Brazil, the first centuries of territory occupation were marked by the presence of scattered populations in coastal areas, increased by the first expeditions, called colonial exploratory expedition, in the seventeenth century. The discovery of gold and precious stones in the eighteenth century in the current states of Minas Gerais, Mato Grosso, Goiás and Bahia contributed to the increase in population, and encouraged the opening of roads, which significantly strengthened the relationships of these areas with the sources of supplies. Many cities that emerged in function of these and other activities have become more important with the intensification of trade, such as port cities. The nineteenth century opened up new perspectives for the settlement of the Brazilian territory, also marked by the beginning of the territory mechanization with the construction of railroads, telegraph and the first shipping companies, resulting in urbanization process in the country (Ferreira, 1959; L.A. Souza, 2004). The phenomenon of urbanization itself only emerged in the mid twentieth century. After the 50s, as a result of industrialization, economic ties and the urban factor became correlated. A new logic in the organization of Brazilian society was established. Economic and social innovations are enormous as they are associated, in this context, to the demographic revolution, the rural exodus and the integration of the territory