Abstract: 　Objective] To study the ultra pathological changes of syncytium of Schistosoma mansoni after cyclosporin A (CsA) treatment. [Methods] MF1 mice were infected with Schistosoma mansoni cercariae. Six weeks later, the adult worms were recovered by portal vein perfusion. After the worms were exposed to CsA of 20 μg/ml for 24 h, the drug induced damage of the worm surface was observed by SEM and TEM. [Results] Incubation of male and female schistosomes with 20 μg/ml of CsA for 24 h resulted in disruption of the tegument and rupture of the spines. Progressive surface damage and swelling and vacuolization of the tegument led to eventual disruption of the syncytium. [Conclusion]The antischistosomal action of CsA is direct, the syncytium is the main site for CsA attack.

Key words: cyclosporin A, Schistosoma mansoni, syncytium, ultrastructure