Abstract: Objective To observe the effect of mefloquine on the tegument of adult Schistosoma japonicum harbored in mice. Methods Twelve mice were each infected with 60-80 S. japonicum cercariae. At 35 days post-infection， 10 mice were treated orally with mefloquine at a single dose of 400 mg/kg. Two mice were sacrificed at 8 h， 24 h， 3 days，7 days， and 14 days post-treatment respectively， and schistosomes were collected by the perfusion technique， fixed and examined under a scanning electron microscope. Schistosomes obtained from the remaining 2 untreated mice served as control. Results 8 h post-treatment，male and female schistosomes showed focal swelling of the worm body accompanied by extensive swelling， tough junction and fusion of tegumental ridges. Meanwhile， some of the sensory structures showed enlargement and part of them collapsed. 24 h after mefloquine administration， head portion of some male and female worms revealed high swelling accompanied by severe damage to oral sucker. 3 days post-treatment，focal swelling of worm body along the whole worm was universal. In some male and female worms，the damaged tegument fused together to form a large mass protruding from the tegumental surface. In addition， focal or extensive peeling of tegumental ridges was seen or collapse of enlarged sensory structure resulted in formation of hole-like appearance. 7 days post administration， focal swelling of worm body and damage to tegument induced by mefloquine were similar to those aforementioned， but focal peeling， collapse of enlarged sensory structures， and deformation of oral sucker in male and female worms were universal. 14 days post-treatment，individual male worm survived the treatment revealed normal appearance of tegumental ridges in head portion， although light focal swelling of worm body was still observed. Conclusion Mefloquine causes focal swelling of worm body， extensive and severe damage to the tegument in adult S. japonicum.

Key words: Mefloquine, Schistosoma japonicum, Schistosomiasis, Scanning electron microscopy