 Thereafter, all residents between 10 and 19 yrs of age will be interviewed at their homes regarding the fulfilment of the inclusionexclusion criteria. Those who fulfil the criteria and agree to participate in the screening phase of the trial signed Screening Informed Consent will be given stool vials and asked to provide stool samples two samples within 5-day intervals that will be collected at their homes in the following days, stored in heat-proof containers and taken to the premises of the Service of Reference for Schistosomiasis Diagnosis of the CPqAM to be promptly prepared for examination by the Kato-Katz method Katz et al, 1972, Rev. Inst. Med. Trop. Sao Paulo, 14: 397-400 aiming to identify positive cases and estimate individual egg load. Females on childbearing age will also be asked to provide a urine sample for pregnancy test. Pregnant women will only be treated with Praziquantel after weaning, as currently recommended by Funasa, and will be excluded from the trial. The 2 stool samples provided by each individual will be analysed for S. mansoni infection. Two slides will be prepared from each stool sample, and the mean value of the 4 slides as measured by number of eggsg of stool will be calculated. Only those harbouring at least 100 epg who are able and willing to follow-up will be invited to participate in the study. At this stage, individuals with positive diagnosis for S. mansoni and that for any reason were excluded from the study will receive standard treatment for schistosomiasis. 