ABSTRACT
Schistosomes are capable of surviving for many years in the blood of their hosts by virtue of their numerous ingenious evasive strategies that allow circumvention of "front line" host immune responses. Epidemiological data of Wilkins strongly suggests that vaccination based on a "natural antigen" approach will be most successful in the case of schistosomiasis hematobia. More epidemiological studies are required to establish that this strong age-related resistance is a universal feature of schistosomiasis hematobia in endemic areas. The importance of knowing how schistosomules and schistosomes can be killed in vivo by naturally occurring or induced immune responses is obvious. Schistosomes that "escape" from the hepatoportal circulation via these collaterals are not recovered at portal perfusion and the host appears to be resistant to infection. The female schistosome lays eggs as undifferentiated embryos that develop in host tissues over a couple of weeks into a mature miracidium ready to hatch from the egg on contact with fresh water.
