Changes on Schistosoma mansoni (Digenea : Schistosomatidae) worm load in Nectomys squamipes (Rodentia : Sigmodontinae) concurrently infected with Echinostoma paraensei (Digenea : Echinostomatidae)

The water rat, Nectomys squamipes, closely involved in schistosomiasis tran smission in Brazil, has been found naturally infected simultaneously by Sch istosoma mansoni and Echinostoma paraensei. Laboratory experiments were con ducted to verify parasitic interaction in concurrent infection. It was repl icated four times with a total of 42 water rats and essayed two times with 90 mice pre-infected with E. paraensei. Rodents were divided into three gro ups in each replication. A wild strain recently isolated from Sumidouro, RJ , and a laboratory strain of S. mansoni from Belo Horizonte (BH) was used. Rats infected with E. paraensei were challenged 4 weeks later with S. manso ni and mice 2 or 6 weeks after the infection with S. mansoni. Necropsy took place 8 weeks following S. mansoni infection. The N. squamipes treatment g roups challenged with S. mansoni RJ strain showed a significant decrease (8 0 and 65%) in the S. mansoni parasite load when compared with their respect ive control groups. There was a significant change or no change in the host s challenged with the BH strain. The persistence time of E. paraensei withi n host was extended in relation to control groups, with a consequent enhanc ement of the number of recovered worm. An E. paraensei strain-specific infl uence on S. mansoni parasitism is reported. This paper presents some experi mental data about this interaction in N. squamipes. and Mus musculus.