Investigations on immunity to schistosomiasis have dealt principally with two main topics: with immunodiagnosis and with methods for producing resistance either by the use of vaccines or by previous infection with irradiated cercariae and with nonhuman strains.
As far as immunodiagnosis is concerned, a large number of serologic tests have been devised that seem to be of help in the diagnosis of chronic infections in which eggs are difficult to find in feces or urine. All of these tests can be carried on with relative simplicity; antigens have been purified to some extent, and the actual tests are very simplified so that they can be used under field conditions. Antigens prepared from cercariae and from adult worms are the most commonly used. The intradermal reaction is also used extensively, and since the nitrogen content of antigens has been standardized, a definite area of the wheal formed after injection can be called a positive reaction.