Tegumental changes in adult Schistosoma mansoni harboured in mice treated with praziquantel enantiomers

Praziquantel administered to the host causes damage to the tegument of Schistosoma mansoni. In this study, the effects of racemic praziquantel (Pra) and its enantiomers, levo-praziquantel (l-Pra) and dextro-praziquantel (d-Pra) were compared using scanning electron microscopy (SEM). Mice infected with S. mansoni for 49 days were treated with a single dose of Pra (300 mg/kg), l-Pra (150 mg/kg) or d-Pra (150 or 600 mg/kg). Groups of three mice were killed after 4 and 24 h, and schistosomes collected by perfusion and examined by SEM. Treatment with Pra or l-Pra, for 4 or 24 h, caused tegumental damage to S. mansoni including severe swelling, vacuolization, fusion of the tegumental ridges and loss or shortening of the spines on the tubercles, collapse and peeling. After treatment with d-Pra at 150 mg/kg, no apparent damage was observed. When the dosage was increased to 600 mg/kg, after 4 h lesions on the tegument similar to those induced by Pra or l-Pra were seen, but less severe. After 24 h, there was evidence of recovery. The study thus clearly showed that l-Pra was more active than d-Pra in causing tegumental damage. d-Pra showed a qualitatively similar activity at a higher concentration. It is possible that this effect was due at least to some extent to the small amount of l-Pra (<2%) which was present in the preparation of d-Pra used.