Parasitological and ecological aspects of Schistosomiasis mansoni in the valley of the Paraíba do Sul River (São Paulo State, Brazil) I. Natural infection of small mammals with Schistosoma mansoni.

Small mammals naturally infected with Schistosoma mansoni were studied in the valley of the Paraíba do Sul river (São Paulo State, Brazil). 192 animals of 12 species were examined post mortem. Cavia aperea, Holochilus brasiliensis leucogaster, Nectomys squamipes squamipes, Oryzomys nigripes eliurus and Zygodontomys brachyurus were found infected. Most schistosome eggs found in the faeces were mature but no eggs were found in the faeces of C. aperea although adults were recovered. In the other infected animals the number of eggs per gram of faeces showed a marked daily variation. Perfusion of the portal system demonstrated that in H. b. leucogaster worms usually remained in the mesenteric veins. In C. aperea 75.7% of worms were found in the portal and intra-hepatic veins. H. b. leucogaster seems to be the rodent most likely to play a role in the epidemiology of schistosomiasis mansoni in the valley of the Paraíba do Sul river.