The water rat,
Nectomys squamipes
, closely involved in schistosomiasis transmission in Brazil, has been found naturally infected simultaneously by
Schistosoma mansoni
and
Echinostoma paraensei
. Laboratory experiments were conducted to verify parasitic interaction in concurrent infection. It was replicated 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 groups 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. mansoni 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 groups challenged with
S. mansoni RJ strain showed a significant decrease (80 and 65%) in the
S. mansoni parasite load when compared with their respective control groups. There was a significant change or no change in the hosts challenged with the BH strain. The persistence time of
E. paraensei within host was extended in relation to control groups, with a consequent enhancement of the number of recovered worm. An
E. paraensei strain-specific influence on
S. mansoni parasitism is reported. This paper presents some experimental data about this interaction in
N. squamipes and
Mus musculus
.
