Hypersensitivity to parasite proteolytic enzyme in schistosomiasis.

A proteolytic enzyme which hydrolyses hemoglobin was obtained from the supernatant fraction of homogenized Schistosoma mansoni. This enzyme elicited histaminic skin reactions in various animals, including man, which were infected with S. mansoni. It failed to induce reactions in monkeys harboring S. haematobium, S. japonicum, or S. intercalatum. In a preliminary field trial in the Caribbean, the skin test proved to be somewhat less sensitive than the customarily used extract of adult worms in Coca's solution. However, the enzyme appeared to induce fewer false positive reactions and delayed responses than did the Coca's extract. A new diagnostic test for schistosomiasis probably could be developed by using specific parasite enzymes against which the host has become sensitized in the course of infection.