Schistosomiasis japonica in Barrio San Antonio, Basey, Samar in the Philippines. IV. "Atypical" precipitates in the circumoval precipitin test--a reaction of recent infection.

Morphologically distinct circumoval precipitin reactions, not having the usual "segmented" appearance, are characteristic of recently acquired infection of man with Schistosoma japonicum. In contrast to the precipitins seen in plasma of those with chronic infections, reactions of recent infection (RRI) are commonly, large, vacuolated blebs or, if elongate, are smooth and vacuolated in structure. Recognition of these RRI provides a practical, simple method to study incidence of infection and the techniques used are readily accepted by children in primary school grades.