Schistosome carbohydrates.

Schistosomes are long-lived in their human hosts (with life-spans measured in years), despite being situated in the blood stream and therefore apparently fully exposed to a wide range of vigorous immunological responses. However, not only have these parasites evolved so as to prosper in the hostile environment of their definitive host, but they also have to negotiate very different environments during the free-living and intermediate host stages of their life cycle. At each stage, surface, or secreted carbohydrates appear to play an important role in the parasite's interaction with its environment.