the effect of mass-chemotherapy in the control of bilharziasis

with the success achieved in the interruption of the transmission of bilharziasis by snail control in most endemic areas of iran, mass-chemotherapy has been used extensively for reducing the number of cases in various villages. niridazol was chosen for this purpose after a screening of several drugs. eight thousand eight .l1undred seventy-four cases in 259 localities were treated from 1966 to the present time. the side-effects encountered were generally mild. this extensive mass-treatment has resulted in a reduction of the prevalence of infection below 10% in the majority of villages in all foci. the overall reduction in the positively rate was 92.2% in 100 villages where transmission had been stopped and 64.4% in 14 villages where transmission had not been stopped. the results of follow-up examinations revealed that only 3 and 2.1% of treated cases, respectively, were still passing viable eggs 3 and 6 months after therapy. the success achieved in this area, in spite of vast programs of irrigation development, is proof that with the schistosomicidal drugs now avails.