Mounting evidence for acquired immunity to schistosomiasis
in humans supports the case for immunological intervention. On the
other hand, apid reinfection poses a threat to younger age groups due
to the slow maturation of natural resistance. However, rational
approaches, based on advances in immunology and molecular biology,
have substantially increased the odds of producing an effective
vaccine. Since the parasite cannot replicate in the human host and serious
morbidity generally occurs only after a relatively long period of heavy
worm burden, complete protection against infection is not essential.
The chances of success would increase if more than one of the various
host/parasite interphases were targeted, for example reducing morbidity
through decreased worm loads as well as through suppression of egg
production.
Several promising schistosome antigens have now reached an advanced phase of
development and are currently undergoing independent confirmatory testing
according to a standardized protocol. A few molecules are being
contemplated for scaled-up production but, so far, only one has reached the
stage of industrial manufacture and safety testing. Since schistosomiasis
cannot realistically be controlled by a single approach, vaccination is
envisaged to be implemented in conjunction with other means of control,
notably chemotherapy.
