The effects of closantel treatment on the ultrastructure of Haemonchus contortus.

H. contortus were recovered from sheep 0-14 h after intramuscular treatment with closantel. Ultrastructural examination revealed that mitochondria were more electron dense and contained swollen cristae compared with untreated controls. Following treatment, the basal channels in the intestine became prominent and there was vesicle formation in all organs examined. In contrast, closantel-resistant H. contortus appeared normal after drug treatment. It is likely that closantel affects membrane associated processes responsible for fluid and ion homeostasis as well as mitochondrial function. Untreated H. contortus were maintained in balanced salt solution for 12 h which caused lesions indicative of fluid imbalance, but at 23 h there were serious structural abnormalities.