Prospects of vaccination against schistosomiasis.

The development of a vaccine against schistosomiasis is necessary in order to reduce the risk of reinfection after drug treatment. Recent reports converge on a message strongly supporting the existence of naturally acquired human immunity to this infection and reinforcing the hypothesis that at least partial protection can be achieved by artificial means. Advances in molecular biology have led to the identification and characterization of an array of protective schistosome antigens, and the introduction of new sophisticated methods for their production enables a bypass of previous low-yielding and labour-intensive procedures. Although vaccination of animals with these antigens does not result in consistent levels of protection exceeding 50%, the reproducible induction of about 80% protection with live attenuated cercariae indicates that immunization against schistosomiasis is achievable. The finding of antibodies capable of blocking protective immunological responses suggests a complicated interaction between different properties of the immune system which needs to be understood and modulated in the direction of improved resistance. An overview of the present status of vaccine development in schistosomiasis including results in different animal models and evidence from field studies on humans is presented and discussed.