Further observation on histopathological alterations of adult Schistosoma japonicum harbored in mice following treatment with mefloquine at a smaller single dose.

The purpose of the present study is to assess the histopathological alterations of adult schistosomes caused by a smaller dose of mefloquine. Mice were infected with Schistosoma japonicum cercariae for 35 days and then treated with a single 200 mg/kg oral dose of mefloquine. Groups of mice were killed between 12 h and 28 days posttreatment, and the livers were removed, fixed, and processed routinely and examined by light microscopy. Twelve hours to 48 h or 3 days posttreatment, 10.3% to 53.3% of male worms and 10% to 25% of female worms shifted to the liver revealed normal appearance. However, 46.7% to 69.2% of male worms and 45.5% to 75% of female worms showed signs of degeneration, including moderate or high swelling of tegument and/or muscles with roughing surface or formation of small vesicles beneath the tegument or collapse of damaged tegument, light swelling of parenchymal tissues, and light dilatation of gut. These histopathological changes aggravated either in extent or in severity along with time, especially the speed of emergence of dead worm granuloma that was faster in female worms than in male ones. In female worms, severe damage to the vitelline glands was universal, which was characterized by necrosis and karyopyknosis of vitelline cells and emergence of small vacuoles among the vitelline gland lobules. Seven days to 28 days posttreatment, almost all of the female worms shifted to the liver were classified as dead or dead worm granuloma, while the percentage of dead male worm and its granuloma examined in the liver was 52.1% to 53.3%. The results indicate that smaller dose of mefloquine (200 mg/kg) still shows strong histopathological response to kill female schistosomes, but its lethal effect against male worms is weakened.