Schistosoma mansoni (Gezira) infection in Biomphalaria pfeifferi snails from Gezira and Jebel Marra.

The comparative susceptibility of Biomphalaria snails from Gezira and Jebel Marra to S. mansoni (Gezira) was investigated. Groups of laboratory-bred snails from the two localities were exposed to 0, 1, 2, 3 and 4 miracidia. The growth rate of the snails was followed over the experimental period by measuring the snails' shell size. Sub-groups of infected snails were examined for daughter sporocyst counts by crushing of the snails. Other groups of exposed snails were maintained until cercariae were shed. The exposed snails grew faster than the controls and growth was not dependent on the number of infecting miracidia. Jebel Marra snails grew faster than the Gezira snails and development of the daughter sporocysts within the snails was temperature dependent. Daughter sporocysts were first found on day 19 after exposure when the laboratory temperature ranged between 18 and 25 degrees C and on day 10 at a range of between 28 and 30 degrees C. Daughter sporocysts and cercarial counts overlapped in numbers per snail exposed to 1, 2, 3 and 4 miracidia for both Gezira and Jebel Marra snails. Nine out of 78 Jebel Marra snails were negative for daughter sporocysts, while all of the Gezira snails were positive. This might indicate greater susceptibility of the Jebel Marra snails to the parasite. Our experiments showed that snails from Jebel Marra are capable of supporting an S. mansoni infection from the Gezira until cercariae are shed. The epidemiological significance of the migrant labourers to the Gezira area in the transmission and spread of intestinal schistosomiasis in Jebel Marra is discussed.