Site potential for challenge attrition in mice, rats and guinea pigs vaccinated with irradiated cercariae of Schistosoma mansoni

The potential sites of attrition of a challenge population of schistosomes have been investigated in mice, rats and guinea pigs vaccinated with irradiated cercariae of Schistosoma mansoni, by the use of challenge regimens that permit sequential site elimination. Vaccinated mice showed significant immunity to a percutaneous cercarial challenge, but were only marginally resistant to an i.v. challenge with healthy lung stage worms. Vaccinated rats and guinea pigs differed from mice, in that they were able to mediate significant challenge attrition at post-skin sites. Healthy lung worms were subject to immune elimination by rats in the lungs, or perhaps en route to the liver, but not in the liver itself. In contrast, guinea pigs had the capacity to kill challenge lung worms injected into either the lungs or the liver. Interestingly, lung worms harvested by extended incubation were shown to be sub-optimal in terms of viability, since they were eliminated in significant numbers when injected i.v. into vaccinated mice. These data show that different hosts vaccinated in essentially the same manner differ in terms of their site potential for challenge attrition. It is emphasised however, that sites implicated by these experiments as having the capacity to mediate immune elimination are not necessarily the sites at which challenge attrition occurs under normal circumstances.