Acute, chronic and late-stage infections with Schistosoma japonicum: reactivity of patient sera in indirect immunofluorescence tests.

Sera from 74 patients with acute, chronic or late-stage schistosomiasis japonica were tested in indirect immunofluorescence tests, with sera of healthy Chinese individuals serving as controls. Cryostat sections of adult Schistosoma japonicum and S. mansoni were used to determine the reactivity of sera with the parenchyma, tegument or gut of the worms. There was inconsistent reactivity between total immunoglobulin and the parenchyma during the acute and chronic stages and hardly any such reactivity in the late stage. Reactivity with the tegument was consistently positive in the acute stage (25 sera) but some chronic-stage sera (four of 32) and most late-stage sera (11 of 17) did not react. In contrast, reactivity with the gut was uniformly strong during the acute and chronic disease, whereas late-stage patients had generally lower titres and one did not react. Similar results were obtained with tests for IgA antibodies, although the titres were generally lower. The homologous reactions with S. japonicum frequently yielded higher titres than the heterologous reactions with S. mansoni, particularly with sera of generally low reactivity. Although the immunofluorescence tests showed limited value in identifying the stage of the disease in individual patients, within the study population, acute, chronic and late-stage schistosomiasis japonica could be distinguished in terms of mean titres.