Seasonality as a determinant of the efficacy of praziquantel in population-based chemotherapy: lessons from the practice.

During October-November 1991, 1356 male farmers, 18-40 years old from a village in Fayoum Governorate, Egypt, were examined for Schistosoma haematobium infection. The prevalence of infection was 22.2%. Infected farmers were treated immediately with praziquantel at the recommended dose of 40 mg/kg body weight in a single, oral dose. Twelve weeks after treatment 86/262 (32.8%) infected farmers were negative for S. haematobium eggs in urine. In another study conducted in a satellite village in the Nile Delta (Beheira Governorate) where S. mansoni infection is prevalent, all residents of both sexes between 5 and 50 years of age (n = 858) were examined for S. mansoni. The prevalence of S. mansoni was 69.0%. Infected subjects were treated with the same dose of praziquantel during January-February 94, with an overall resultant efficacy of 85.5% (471/551) and 97.2% (103/106) in 18-40 years old males 8-10 weeks post treatment. The high cure rate in the second study was probably because treatment took place 2 months after the end of the high transmission season.