The present study investigated whether Schistosoma japonicum or Schistosoma bovis could establish prenatally in lambs. Three ewes were exposed to S. japonicum by intramuscular injection of cercariae, and 3 ewes were exposed to S. bovis cercariae using the leg-emerging technique approximately 2 mo before delivery, and 1 age-matched pregnant ewe served as an uninfected control. The study lasted 18–20 wk after infection, which was 8–9 wk after delivery. All 6 exposed ewes became infected with either S. bovis or S. japonicum. Eight lambs were borne by the 7 ewes, of which 1 (S. bovis exposed) was dead and 1 (S. japonicum exposed) died at delivery. Of the 3 S. japonicum-exposed lambs, 2 were found infected. Four lambs born of S. bovis-exposed ewes were negative. Despite having no worms, these 4 S. bovis-exposed lambs as well as the 1 negative S. japonicum-exposed lamb had, in contrast to the nonexposed control lamb, few, but distinct, liver granulomas dominated by eosinophils and giant cells with large central necrotic areas but with no remnants of eggs or worms. Hence, congenital infection was demonstrated in S. japonicum-infected lambs, but not in S. bovis-infected ones.

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