Studies on larval digeneans infecting freshwater snails.

The present study examined the diversity, taxonomy and population biology of digenean larvae infecting fresh water snails in five habitats in Dar es Salaam, Ruvu and Morogoro. A total of 9424 snails belonging to 12 species and five families were examined for digenean infection in which 20 morphologically distinguishable cercariae were recovered. Nine cercariae were identified. These were Cercaria no. I (Schistosoma haematobium Bilharz, 1852), Cercaria no. II (S. mansoni Sambon, 1907), Cercaria no. IV (reptilian schistosome), Cercaria no. VII (avian schistosome), Cercaria no. VIII (Cercaria species near ocellatta La Vallete, 1855), Cercaria no. IX (Cercaria species near vivax Sonsino, 1892), Cercaria no. X (Cercaria species near decora Fain, 1953), Cercaria no. XV (Cercaria species near kunga Fain, 1953), and Cercaria no. XVII (Sphaediotrema species near globolus Szidat, 1937). The eleven unidentified cercariae were considered as new descriptions. Prevalence of digenean larvae in their respective snail hosts was found to be low and varied with seasons. Prevalence also varied among snail hosts, was highest in Lymnaea natalensis followed by Bulinus tropicus. In addition, prevalence varied among habitats. Highest prevalence was recorded at Kinondoni pond and lowest at Ruvu ponds. Prevalence was also found to increase with host size in L. natalensis, B. tropicus and B. globosus. Factors influencing prevalence are discussed. Argentophilic papillae patterns (chaetotaxy) were studied using light microscopy on the surface of furcocercous, echinostome and xiphidiocercariae. It was found that papillae patterns are species specific and related species show resemblance while unrelated species show complete patterns. The usefulness of papillae patterns in separating cercarial species is discussed.