Benzimidazole resistance in equine cyathostomins in India

• Widespread prevalence of benzimidazole resistance in equine cyathostomes was detected in Uttar Pradesh, India.
• Resistant alleles were significantly higher in cyathostomins of intensively managed horses.
• Higher proportions of heterozygous individuals were detected in working horses.
• Emergence of benzimidazole resistance in working horses is a serious concern in India.

Benzimidazole resistance is a major hindrance to the control of equine cyathostominosis throughout the world. There is a paucity of knowledge on the level of benzimidazole resistance in small strongyles of horses in India. In the present study, allele-specific PCR (AS-PCR) that detects F200Y mutation of the isotype 1 β-tubulin gene and faecal egg count reduction test (FECRT) were used for detecting benzimidazole resistance in equine cyathostomin populations in different agro-climatic zones of Uttar Pradesh, India. Results of the FECRT revealed prevalence of benzimidazole resistance in cyathostomins in an intensively managed equine farm in the mid-western plain (FECR = 27.5%, LCI = 0) and in working horses (extensively managed) at three locations in central plains of Uttar Pradesh (FECR = 75.7–83.6%, LCI = 29–57%). Post-treatment larval cultures revealed the presence of exclusively cyathostomin larvae. Genotyping of cyathostomin larvae by AS-PCR revealed that the frequency of homozygous resistant (rr) individuals and the resistant allele frequency was significantly higher (p < 0.001) in the intensively managed farm in the mid-western plain and in working horses at two locations in central plains of the state. The resistant allele (r) frequency in cyathostomins was significantly higher (p < 0.05) in Vindhyan and Tarai and Bhabar zones of Uttar Pradesh. The prevalence of benzimidazole resistant allele (r) was significantly higher (p < 0.05) in cyathostomins of intensively managed horses (allelic frequency—0.35) as compared to extensively managed horses (allelic frequency—0.22). The widespread prevalence of benzimidazole resistant alleles in equine cyathostomins in Uttar Pradesh, India, necessitates immediate replacement of the drugs of benzimidazole group with other unrelated effective anthelmintics for management and control of equine cyathostomins.