The abundance of digenean larvae in snails at a pond in Mbezi-Temboni, Dar es Salaam, was investigated from July 1996 to June 1997. A total of 2,112 snails belonging to three species, Bulinus globosus Morelet 1866, Bulinus forskalii Ehrenberg 1869, and Melanoides tuberculata Müller 1774 were examined, and 28 (1.3%) were found infected by four species of digenean trematodes. Trematodes were recovered only from Bulinus species; none of the examined M. tuberculata was infected. B. globosus was infected by Schistosoma haematobium Bilharz 1852 (1.14%), unidentified furcocercous cercariae (0.4%), and echinostome cercariae (0.76%). B. forskalii was infected by echinostome cercariae (0.25%) only, Generally, prevalence of digenean larvae in their host snails was very low and varied with the seasons. Variation of prevalence with the seasons was probably influenced by factors such as rainfall, population dynamics of host, and temporal availability of definitive hosts. Furthermore, S. haematobium and echinostome cercariae from B. globosus occurred alternately but not concurrently, suggesting a possible presence of intramolluscan competition.
Kigadye et al. (Mon,) studied this question.