Schistosoma mansoni: liver phase challenge attrition is a stage-dependent phenomenon in guinea-pigs vaccinated with highly irradiated cercariae.

Guinea-pigs vaccinated with highly irradiated cercariae of Schistosoma mansoni have been examined for their ability to kill challenge parasites at the level of the liver. Skin and lung phase attrition were eliminated by surgical introduction of 4/5 day old schistosomula, or 2, 3 or 6 week schistosomes into the mesenteric vasculature of vaccinated and naive animals. These experiments showed consistently that lung schistosomula and 2 week old parasites were killed preferentially by sensitized animals, but that older worms were refractory. Liver phase immune elimination would therefore seem to be a stage-dependent phenomenon in the vaccinated guinea pig model of schistosomiasis.