Drug Resistance Assessment of Commonly Used Anthelmintics, and Their Combination Effect in Naturally Infected Sheep: The Case of Kaffa Zone, Southwestern Ethiopia
Nahom Belay, Asrat Arke, Lamrot TesfayeABSTRACT
Background
Gastrointestinal nematode (GIN) infections are widely distributed across the country and are responsible for considerable losses in small ruminant production and the emergence of anthelmintic resistance has intensified the challenge. This study evaluated the efficacy of widely used commercial anthelmintics and examined whether combining different drug classes enhances their effectiveness in naturally infected sheep in Kaffa Zone.
Materials and Methods
An experimental trial was conducted using 275 sheep that shed at least 150 eggs per gram count, randomly divided into six groups. Faecal samples were collected from each animal before and after treatment using selected anthelmintics, and the faecal egg count reduction test was employed to identify resistance towards each drug.
Results
Faecal egg count reduction test values and corresponding lower 95% confidence limit were 90.31% and 88.51% for albendazole, 91.39% and 89.53% for tetramisole, and 95.84% and 95.05% for ivermectin, respectively. The findings indicated reduced effectiveness of albendazole and tetramisole, while ivermectin maintained acceptable efficacy. Combination treatments showed markedly higher reductions—99.11% for albendazole with ivermectin and 99.27% for tetramisole with ivermectin. The range of faecal egg counts of infected sheep was from 350 to 6750 EPG before treatment and from 0 to 1550 EPG after treatment. The overall mean of faecal egg counts of infected sheep was 1881.5 ± 69.7 (95% CI: 1744.2–2018.9) and 229.9 ± 28.4 (95% CI: 174.1–285.8) pre‐treatment and post‐treatment, respectively.
Conclusion
The findings suggest the presence of emerging anthelmintic resistance to albendazole and tetramisole in the study area and highlight the potential usefulness of combination anthelmintic strategies. Continued monitoring and integrated parasite management practices are recommended.