The efficacy of human schistosomicide treatment may depend on the rate of transmission.

The efficacy of different treatment protocols in humans infected with Schistosoma mansoni at sites with different transmission conditions was evaluated by the disappearance of anti-worm intestine IgM antibodies in an indirect fluorescence antibody test (IgM-IFT) and anti-egg antibodies in the circumoval precipitin test (COPT). Patient sera coming from sites of active low transmission (ALT), active high transmission (AHT) and low interrupted transmission (LIT) from Venezuela were studied. Chemotherapy protocols were (1) ALT, 60 mg/kg praziquantel (Pzq60); (2) AHT, one dose of 40 mg/kg Pzq followed by one dose of 20 mg/kg oxamniquine for one group and one dose of 40 mg/kg Pzq alone for the other group; (3) LIT, one dose of 40 mg/kg Pzq repeated every 3 months up to three doses. Cure rates occurred mostly between 3 and 12 months with the exception of Pzq60-ALT where it was evident before 3 months. Higher cure rates were evident in both places of low transmission (ALT and LIT) and the lowest in the AHT regardless of the treatment protocol. Cure was more evident with COPT compared to IgM-IFT. The rate of serological cure appears then to depend on the previous state of transmission. The differential cure rate evaluated by both techniques is probably due to the persistence of antibodies against antigens in different stages of the parasite.