The effect of praziquantel on the pseudophyllidean cestodeBothriocephalus acheilognathi in vitro

Abstract

AdultBothriocephalus acheilognathi were incubated in solutions containing 0 (control), 0.1, 1.0, 10.0 and 100 μg praziquantel per ml (0, 10², 10³, 10⁴ and 10⁵ μgl⁻¹) of 0.9% saline for 5, 15 and 60 min at a temperature of 18°C. The worms contracted immediately upon being placed in the drug. Scanning and transmission electron microscopy revealed considerable tegumental damage particularly in the neck region. Vacuolization and ‘bubbling’ to the tegument occurred in all of the drug solutions tested. Exposure to drug concentrations of more than 1.0 μgml⁻¹ (10³ μgl⁻¹) praziquantel for 15 min or greater resulted in many of the ‘bubbles’ bursting and releasing their contents to the exterior. Mature proglottides were distorted and had occasional large swellings resulting in the mass expulsion of eggs. Praziquantel had no ovicidal activity. Exposure to drug concentrations of 100 μg (10⁵ μgl⁻¹) praziquantel per ml saline for 24 h was not lethal to the worms.