Spatial distribution and seasonality of Biomphalaria spp. in São Luís (Maranhão, Brazil).

Two of the three vector species of Schistosoma mansoni Sambon, 1907 in Brazil occur in the state of Maranhão: Biomphalaria glabrata (Say, 1818) and Biomphalaria straminea (Dunker, 1848). For the implementation of effective measures to combat schistosomiasis, it is necessary to identify the spatial and seasonal dynamics of these snails. Therefore, this work brought together information from malacological survey carried out in São Luís (Maranhão, Brazil) to identify the spatial and seasonal distribution patterns of Biomphalaria spp. snails. We used data from malacological surveys of the Municipal Health Secretary of São Luís, conducted between 2006 and 2013 in 23 neighborhoods. We also used data from the mollusk surveys that we conducted for 2 years (2012-2014) in four of these neighborhoods. During the 8-year period (2006-2013), 15,990 specimens of Biomphalaria spp. were collected. There was a positive association between precipitation and the abundance of mollusks of the genus Biomphalaria. During 2012-2014, a total of 2487 snail specimens were obtained (B. glabrata: 1046 specimens; B. straminea: 1426 specimens). There was a positive correlation between precipitation and B. straminea abundance. High density of human occupation and high precipitation are two factors that affect the distribution and density of Biomphalaria spp.