Lack of efficacy of monepantel against Haemonchus contortus and Trichostrongylus spp in small ruminants

Infections with trichostrongylid worms are common and a major cause of production loss in small ruminants worldwide. In Australia, infections with Haemonchus contortus and Trichostrongylus spp cost the Australian sheep industry up to AUD$369 million annually. Currently, the control of these two parasites relies heavily on the use of anthelmintics and grazing management. However, the frequent use of drugs resulted in widespread development of anthelmintics resistance in many trychostrongylid species including H. contortus and Trichostrongylus spp. Monepantel (Zolvix®, Novartis, Australia), an amino-acetonitrile derivate, is one of the most recent anthelmintics released in Australia and it proved to be active against strains of H. contortus and Trichostrongylus spp that are resistant to broad-spectrum anthelmintics. However, lack of efficacy of monepantel against Teladorsagia circumcincta and T. colubriformis was recently reported in New Zealand and Australia. In this trial, the efficacy of monepantel in sheep and goats naturally infected with H. contortus and Trichostrongylus spp was assessed by faecal egg count reduction tests (FECRT) and total worm counts (WC).