Variations of titers of immunofluorescent antibody against cercaria, adult and egg antigens developed in rabbits infected with Schistosoma japonicum before and after treatment with praziquantel.

The antibody titers of Schistosoma japonicum infected rabbits were examined against different antigens in various stages of S. japonicum using the indirect immunofluorescent antibody test with FITC-labeled anti-rabbit-gamma-globulin. The first immunofluorescent reaction could be demonstrated in the gut of adult worms 3 to 4 weeks after infection, depending on the strength of infection, then 2 weeks later within the egg shell and on the cercaria and about 1 more week later in the tegument of adult schistosomes. Treatment with praziquantel resulted in a remarkable decrease of the titers with cercaria antigen and in only a gradual decrease with egg, tegument and gut antigen. Therefore cercaria antigen seemed to be the most reliable index of successful treatment. The high sensitivity of gut and egg antigen might lead to difficulties to distinguish the successfully treated cases from chronic cases of S. japonicum infections.