Passive avoidance response in mice infected with Schistosoma mansoni.

Schistosomiasis is a parasitic disease of humans and rodents affecting more than 200 million people worldwide. Following the onset of infection, the worms induce granulomas around schistosome eggs in the liver, intestine and central nervous system (both brain and spinal cord), which are likely to cause changes in cognitive functions. In the present study, CD-1 female mice were percutaneously infected with 60 cercariae of Schistosoma mansoni and the effect on the mice's cognitive abilities were assessed by using the passive avoidance learning paradigm both in an early and a late phase of infection (independent groups). The results of the study show that infected animals without brain granulomas (early phase) had impairments in their passive avoidance response, whereas mice with brain granulomas (late phase) behaved as uninfected ones. Moreover, a decreased propensity to start exploration was observed in mice with granulomas in the brain. The results suggest that the murine model of infection may be a useful tool for studying human neuroschistosomiasis.