Histopathological alteration of juvenile Schistosoma japonicum in mice following treatment with single-dose mefloquine

This study aims to observe the histopathological alterations in schistosomula of Schistosoma japonicum induced by mefloquine. Mice were infected with S. japonicum cercariae, and after 14 days, a single dose of mefloquine (400 mg/kg) was administered orally. After 8 h, 24 h, 3 days, 7 days, and 14 days, groups of two to three mice were sacrificed, and livers were removed, fixed and processed routinely, and examined by light microscopy. After 8 h, 51.5% of the schistosomula examined showed degeneration, which included high dilatation of gut, desquamation of gut epithelial cells, swelling of tegument, muscles, and parenchymal tissues, and adherence of inflammatory cells to the damaged tegument of the juveniles. After 24 h, the percentage of dead worm and degenerated worm were 43.2% and 48.4%, respectively, and the intensity of damage increased, including severe swelling and vesiculation of tegument, collapse of damaged gut, and loss of definition in the internal structure. In addition, dead worms were infiltrated by eosinophil-predominated inflammatory cells. After 3 days, more than 96% of schistosomula were severely degenerated and dead, and some of them were focally or extensively infiltrated by inflammatory cells accompanied by necrosis of internal structure. Seven to 14 days after treatment, most dead schistosomula developed to dead worm granulomas with the percentages of 60.1–86.3%, while those of dead schistosomula were 26.7–8.4%. The results indicate that mefloquine exhibits an extensive and severe damage to juvenile S. japonicum harbored in mice.