Schistosomiasis Research Group

There are at least two laboratory animal models where the parasites establish but are then eliminated in a self-cure response, that might form the basis for a vaccine. In the laboratory rat this occurs around four weeks after a primary infection when the worms are in the portal veins of the liver, coincident with rising IgE levels in the circulation and hepatic mast cell degranulation (Cutts & Wilson 1997; Miller et al. 1994). Whilst such a mechanism might be difficult to replicate in a vaccine, the antigens that trigger the protective response could represent a chink in the parasite’s armour.

The rhesus monkey is an altogether more promising model where our recent observations, in collaboration with researchers at BPRC, Rijswijk, The Netherlands, suggest that parasite elimination, occurring between 12 and 18 weeks after infection, correlates with IgG levels. As a result of immune pressure, the mature worms in the portal system first cease egg laying, then blood feeding and eventually starve to death. We are devising techniques to collect and characterise the gut secretions of adult worms (at present only 2-3 proteases have been identified). Apart from the parasite eggs, these gut secretions represent the major source of material released by the adults into the host bloodstream and hence a likely source of antigens relevant to the two self-cure models.