Integrated epidemiology and multi-assay evidence of anthelmintic resistance in ovine gastrointestinal nematodes of Northern India

Gastrointestinal parasitic (GIP) infections are a major constraint to sustainable small ruminant production worldwide due to increasing anthelmintic resistance caused by extensive reliance on chemical anthelmintics. In this study, a total of 2308 faecal samples were collected and examined from naturally infected sheep across northern India, encompassing 15 districts of Punjab and 07 of Himachal Pradesh. An overall prevalence of 96.4% for GIP infections was recorded with strongyles being predominant followed by coccidia. Quantitative faecal examination revealed 62.6% light, 10.2% moderate and 27.2% severe nematode infection with Haemonchus (60.0%) being the most prevalent genera as per coproculture examination. The logistic regression analysis revealed season and deworming status to be the significantly associated risk factors with prevalence of GIPs. The efficacy of fenbendazole, levamisole and ivermectin was evaluated at 14 sheep farms across the study region by in-vivo (faecal egg count reduction test, FECRT) and in-vitro assays (egg hatch test, larval development assay). The findings of FECRT revealed multi-anthelmintic resistance status (resistance against more than one class of anthelmintic) across all farms with an overall percent efficacy (mean ± SE) for fenbendazole, levamisole and ivermectin as 61.6 ± 5.0%, 57.4 ± 6.4% and 57.4 ± 5.2%, respectively. Results of in-vitro assays revealed 78.6%, 78.6% and 100% sheep farms as resistant against fenbendazole, levamisole and ivermectin, respectively. The high prevalence of GINs can be linked to its resistant status observed against commonly used anthelmintics, highlighting the need to investigate novel chemical and non-chemical approaches for effective worm management in the region.