Availability, Distribution and Infectivity of Freshwater Snails with Helminth Parasites in Selected Sites of Sokoto State, Nigeria

Distribution of snails was determined from six collection sites of Kware and Wamakko Local Government Areas of Sokoto State. The sampling sites for snail collection were sides or edges of freshwater ponds, slow moving streams, lakes, irrigation canals and rivers found around the villages and towns in which the sampling sites were located. Scoop net was employed in the collection of freshwater snail samples, the collected snails were counted and expressed as the number of snail species per 10 scooping. The snails were identified by the Museum of Natural History, Department of Zoology, ABU, Zaria and using the key to freshwater biology. The snails were taken to laboratory, placed in aquaria with tap water for acclimatization in 48 hours before screening for infectivity with cercariae. Different freshwater snails found from sites of the study were identified as Bulinus globosus, Biomphalaria glabrata, Radix natalensis, Melanoides maculatus, Bellamya cascarillas, Bellamya crawshayi and Lanistes ovum. B. globosus was the species with high number of 46% and distribution while, B. crawshayi was species with low number of 2.8% and least population. The snails were screened for infectivity with cercariae by placing them individually in glass jars (about 10 snails) per aquarium and were exposed to day light for 6 hours. Additional illumination of 100w electrical bulb was provided. The snails were subjected to abrupt reduction of temperature by at least 5oC by placing ice block in the aquarium to facilitate the emergence of cercariae. Three of the seven snail species collected (Bulinus globosus, Biomphalaria glabrata and Redis natalensis) shed cercariae of different morphological characteristics, swimming behaviours and resting positions. Out of the 117 cercariae released, 67 (57.3%) of S. haematobium were isolated from B. globosus, 38 (32.5%) of F. hepatica were isolated from R. natalensis, 12 (10.2%) of S. mansoni were isolated from B. glabrata and non were isolated from M. merculatus the result of the study indicated infectivity of the three snail species and thus, confirmation of their roles as vectors of schistosomiasis and fascioliasis in the study area. Chemical and phytol-molluscicides are therefore recommended to control population of snail vectors as well as the prevalence of schistosomiasis and fascioliasis. Further research on freshwater snail vectors of helminth disease agents is also recommended.