Small mammals are found naturally infected by Schistosoma mansoni, becoming a confounding factor for control programs of
schistosomiasis in endemic areas. The aims of this study were: to investigate the
infection rates by S. mansoni on the water-rat Nectomys squamipes during four years in endemic areas of Sumidouro, state of Rio de Janeiro, using mark-recapture technique; to compare two diagnostic methods for
schistosomiasis; and to evaluate the effects of the
chemotherapy in the human infected population on the rodent
infection rates. The rodent
infection rates of S. mansoni increased when rodent population sizes were lower. Coprology and serology results presented the same trends along time and were correlated. Serology could detect recent
infection, including the false negatives in the coprology. The
chemotherapy in the humans could not interrupt the rodent
infection. Rodents can increase the schistosomiaisis transmission where it already exists, they probably maintain the transmission cycle in the nature and can be considered as
biological indicators of the transmission sites of this parasite since they are highly susceptible to
infection. The water-rats may present different levels of importance in the transmission dynamics of S. mansoni
infection cycle for each area, and can be considered important wild-reservoirs of this human disease.