A Study of Schistosomiasis Prevalence and Risk of Snail Presence Spatial Distributions Using Geo-Statistical Tools

Abstract

Schistosomiasis mansoni is an endemic disease, typical of developing countries. In Brazil, schistosomiasis is caused by the etiological agent Schistosoma mansoni, whose intermediate hosts are species of mollusc of the Biomphalaria genus. It is a fact, accepted by almost all the researchers, that S. mansoni was introduced in Brazil by the African slavery trade during the sixteenth century (Almeida Machado, 1982). It was in the northeast of Brazil that the sugar cane found fertile and favourable soil, especially in the coastal plains with their hot and humid climate, where today the states of Pernambuco and Bahia are located. The scarce manpower, obtained from the native Indian, did not meet demand and it was more profitable to import slave labour from Africa. From the mid-sixteenth century (1551-1575) until mid-nineteenth century (1851-1860) about four million slaves arrived in Brazil. This migration started in the main African regions of the west, the east, southwest and Mozambique. Although many regions of Africa supplied slave labour to Brazil, the majority originated from the Congo and Angola. The Portuguese colonization of Angola in the early sixteenth century, enabled the migration of more than two thirds of Africans, from the ports of Luanda, Benguela and Cabinda. During the sixteenth and early seventeenth centuries, there was a large influx of Africans from the ports of the Bay of Benin (region of Ghana/Nigeria). The Brazilian port of Salvador and Recife received most of the slaves (Klein, 2002), originated from endemic regions of both S. mansoni and S. haematobium infections. However, the absence of an intermediate host for S. haematobium in Brazil was a limiting factor which minimized the later problem in the country (Camargo, 1980). The wetlands used for planting sugar cane almost always follow the rivers’ banks and streams and the presence of molluscs of the Biomphalaria genus, susceptible to S. mansoni, provided the ideal environmental conditions for the schistosomiasis introduction into the country (Camargo, 1980). The endemic area has remained unchanged for several years, probably due to the shortage at that time of roads and transportation, hampering the population movement (Camargo, 1980).