Distribution of freshwater snails in the river Niger basin in Mali with special reference to the intermediate hosts of schistosomes

Abstract

Snail surveys were carried out in various parts of Mali . All areas surveyed are part of the Niger basin being either affluents or irrigation schemes fed by this river . The snail species present varied greatly between areas .The following potential hosts of schistosomes were recorded : Biomphalaria pfeifferi, Bulinus truncatus, B, globosus, B. umbilicatus, B. forskalii and B. senegalensis.In the large irrigation schemes, i .e. `Office du Niger' and Baguineda, only B, pfeifferi and B. truncatus appear to be intermediate hosts . Snail distribution appeared to some extent to be focal and high snail densities appeared to be associated with human water contact activities, which apparently create favourable biotopes for the snails . This is probably due to an alteration of the vegetation and an increase of the trophic status of the site by contamination with food remnants and other debris . The larger irrigation canals or lakes in these schemes play an important role in the transmission of human schistosomes and transmission appears to be very focal in these habitats . Infected snails are almost exclusively found in well-defined human water contact sites (WCS) . Local infection rates with schistosomes were often high (i .e. up to 27% in B, pfeifferi) .In urban areas (i .e. Bamako), transmission patterns are more variable . In Bamako schistosome-infected B.truncatus were found in the Niger river . A number of smaller semi-permanent or permanent streams are very important transmission sites, and schistosome infections were recorded from B. pfeifferi, B. truncatus and B. globosus. Schistosome infection rates in B. pfeifferi were often high (up to 30%).In a new lake at Selingue, B. truncatus was found to be widely distributed only about a year and a half after the dam was constructed, and in some sites schistosome infections were recorded .

Schistosomiasis in Lake Malaŵi Villages

“…B. globosus and B. nyassanus. Bulinus globosus (Morelet 1866) is found in most of the sub-Saharan Africa in various freshwater habitats including streams, rivers, seasonal pools and lakes (Brown, 1994;Mandahl-Barth, 1972;Cantrell, 1981;Madsen et al, 1987;Ndifon and Ukoli, 1989). Bulinus nyassanus (Smith, 1877) is a member of the B. truncatus/tropicus group and is endemic to Lake Malaŵ i; it is found on open sandy areas and has a preference for habitats devoid of vegetation and with substratum consisting of coarse and, to a smaller extent, fine sand, where it is normally found in the upper 2-3 cm of the substratum (Wright et al, 1967;Louda et al, 1983;Phiri et al, 2001;Madsen et al, 2004).…”

Current status of fish-borne zoonotic trematode infections in Gia Vien district, Ninh Binh province, Vietnam

“…Snails were collected during the morning hours for 20 minutes per site by scooping [ 37 , 38 ] and/or hand-picking, transferred to plastic containers and transported alive to the laboratory where they were identified according to keys by Brandt [ 39 ] and Dang [ 40 ].…”

Trematode infections in cattle in Arumeru District, Tanzania are associated with irrigation

“…Collection of snails was performed by scooping [17,18] and or hand picking conducted by two people at each site for 20 min. Snails were identified morphologically using a field guide to African freshwater snails [19,20].…”