Loperamid, an efficacious drug against fish-pathogenic acanthocephalans.

A total of 20 drugs were tested for their efficacy in the treatment of infections involving the two major acanthocephalans infesting rainbow trout in European trout farms. In in vitro experiments, the antidiarrhoeic loperamid and the well-known anthelminthic drug niclosamide showed the best efficacy. Worms treated with loperamid contracted the posterior end of their body, in which severe necrosis of the tegument caused the death of the worms. In in vivo experiments, loperamid was the most efficacious drug: 50 mg/kg given to rainbow trout on 3 consecutive days led to a complete cure. According to preliminary tolerance tests in water baths, the toxicity of this drug is low as compared with that of niclosamide, which is very toxic. Thus, loperamid can be recommended as the drug of choice for therapy of acanthocephalan infections in fish.