Multiple-resistance to ivermectin and benzimidazole of a Haemonchus contortus population in a sheep flock from mainland France, first report.

Anthelmintic resistance was explored by fecal egg count reduction test in a sheep flock from the French Pyrenees at the request of the veterinary practitioner after a poor response to anthelmintics was noted. The FECRT confirmed the suspicion with a mean percentage of reduction in egg excretions of 45% (CI 95%: - 40 to 78.5) and 0% (CI95%: - 162 to 49) within the ivermectin and the benzimidazole groups respectively. Haemonchus contortus was shown to be the IVM and BZ resistant species after morphological and molecular characterizations whereas Teladorsagia circumcincta was probably resistant to BZ only. The H. contortus population was still susceptible to moxidectin, closantel and levamisole. As this sheep flock is a transhumant flock, the spread of this multiple-resistant Haemonchus contortus population to the other sheep flocks sharing the same pastures in Pyrenean Mountains is highly likely. From the knowledge of the authors, this is the first report of multi-resistance to ivermectin and benzimidazole of a Haemonchus contortus population in mainland France.