The effect of pre-exposure to Fasciola hepatica or Schistosoma mansoni on challenge infection with Fasciola hepatica.

Two groups of 12 and 6 rats were inoculated with Fasciola hepatica and Schistosoma mansoni, respectively. The Schistosoma-inoculated group, as well as 6 Fasciola-inoculated rats and 6 uninfected rats were challenged 8 weeks later with F. hepatica. A control group of 6 rats was left unexposed. Eight weeks after the challenge exposure all rats were necropsied and subjected to post-mortem examination. The number of Fasciola recovered after challenge was lower in both groups of rats primarily infected with F. hepatica or S. mansoni. F. hepatica-induced pathological changes were observed in all infected rats, but were pronounced in the group which was first exposed at the time of challenge of the primarily infected groups. No Schistosoma eggs or adults were detected in Schistosoma-inoculated rats. The results demonstrated that rats primarily infected with F. hepatica acquired resistance against a challenge exposure to the homologous parasite. Also S. mansoni, even without patency, can provide partial protection against F. hepatica infection.