Representative images of mouse livers and spleens are shown: uninfected mice (naive), bisexual infected control (mf/mf), infected bisexual control (-/mf), primary infection with male cercariae (m/mf), primary infection with female cercariae (f/mf). (A) Macroscopic assessment of livers and spleens reveals less pronounced organ changes in group f/mf than in mf/mf, -/mf and m/mf. (B) Reduction in liver and spleen indexes in group f/mf indicates that a primary infection with female S. mansoni cercariae has a beneficial effect on disease progression. Data are presented as mean ± SD. (C) Serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (AP) are presented as mean ± SD. (D) Numbers of worm pairs and hepatic eggs are given as mean ± SD. P≤0.05 was considered to be statistically significant.