Efficacy of eprinomectin 5 mg/mL topical solution administered pour on at 1 mg per kg body weight against Przhevalskiana silenus myiasis in goats

Abstract

The larvae of the goat warble fly, Przhevalskiana silenus, chiefly parasitize domestic goats. Its occurrence in Europe is restricted to the southeastern Mediterranean and the southern Balkans; however, the parasite is prevalent and of considerable economic impact in the Middle East and in parts of Asia. Eprinomectin 5 mg/mL topical solution (EPRINEX® Multi, Boehringer Ingelheim) administered at 1 mg eprinomectin per kg body weight pour on was recently authorized as an anthelmintic for sheep and goats with zero hours milk withdrawal in several European countries. Considering that the product in cattle has claims against a broad range of parasites including infestation with warble fly larvae (Hypoderma spp.), this study aimed to test the efficacy of eprinomectin 5 mg/mL topical solution against P. silenus myiasis in goats. Forty-five goats sourced from a farm with a history of P. silenus infestation were randomly assigned to three groups of 15 animals each. Group 1 was untreated (control) while Groups 2 and 3 were treated once with eprinomectin 5 mg/mL topical solution at 1 mL per 5 kg body weight, either in the absence of clinical evidence of P. silenus larvae (Day 0, Group 2) or after warbles had formed (Day 167, Group 3). Goats were examined for warbles on Days 89, 103, 117, 131, 163, 174 and 181, and larvae were collected, examined for viability and speciated. On Day 186, the goats were euthanized, skinned, and examined for remaining larvae. No live larvae were recovered from goats included in treated groups while live larvae were collected from six of the 15 untreated animals (1–3 per animal) (P < 0.01 at α=0.05) demonstrating complete efficacy of the treatments. All larvae collected were identified as P. silenus. The administration of the treatments was well accepted by all animals and no related adverse events were observed. Eprinomectin 5 mg/mL topical solution was demonstrated to be an efficacious and safe treatment against P. silenus myiasis both when the larvae of P. silenus were expected to be L1/L2 and before skin damage occur, and when warbles with L3 have already developed.