Multi-drug resistant Haemonchus contortus in a sheep flock in Antioquia, Colombia

- The Colombian situation on anthelmintinc resistance is largely unknown due to the absence of veterinary diagnostic services.
- Antihelmintic resistance was evaluated in a sheep farm experiencing high lamb mortality and poor body conditions of ewes due to haemonchosis.
- Complete lack of in vivo efficacy was detected for recommended dosages of albendazole, ivermectin, levamisole plus tricabendazol.
- Moxidectin and trichlofon reduced FEC by 75% and 38%, respectively. DrenchRite assay confirmed the in vivo results.

A sheep farm experiencing high lamb mortality and poor body conditions of ewes due to haemonchosis was tested for the presence of anthelmintic-resistant nematodes in August 2014. A fecal egg count reduction test was performed in Colombia on this farm and a DrenchRite® Larval development Assay (LDA) was shipped to the University of Georgia in the United States for resistance testing. The fecal egg count reduction test (FECRT) was conducted on 70 out of 500 animals allocated into five groups of 14 animals each: untreated control, albendazole (ABZ; 3.5 mg/kg sc), ivermectin (IVM; 0.2 mg/kg sc), moxidectin (MOX; 0.2 mg/kg sc) and levamisole (LEV; 5 mg/kg sc) plus triclabendazol/ivermectin (TBZ; 10 mg/kg and IVM; 0.2 mg/kg po). Individual fecal egg counts (FEC) using the modified McMaster technique and pooled larval cultures were performed 10 days after anthelmintic treatment. Following 10 days the initial results from the ABZ and IVM groups, 24 animals were treated twice with trichlorfon (TCF; 50 mg/kg po) on days 0 and 6, and then checked for FEC on day 10. Mean differences in FEC before and after treatment were negligible (3 to 8% change) for the control, ABZ, LEV-TBZ and IVM groups. The MOX treatment resulted a mean FEC reduction of 76.7%, which was not-significant by t-test (p = 0.08). The TCF treatment showed a mean FEC reduction of 42.3%, which was also not-significant (p = 0.1). The DrenchRite® LDA was used to evaluate the resistance status to benzimidazole, levamisole, ivermectin and moxidectin on this farm. Coprocultures indicated that the predominant worm species was Haemonchus contortus (Colombia 94-100%) (UGA 77% H. contortus and 23% Trichostrongylus colubriformis). Resistance was evaluated for both H. contortus and T. colubriformis. The LDA results indicated high resistance to all 4 anthelmintics for both parasite species. The current study, together with similar surveys in 4 other Antioquian goat and sheep farms, confirms the presence of multi-drug resistant H. contortus to all three classes of anthelmintics in this region of Colombia.