Benzimidazole resistance in equine cyathostomins in India.

The research paper investigates the level of benzimidazole resistance in a type of horse parasite in Uttar Pradesh, India, indicating that increased resistance to this commonly used deworming medicine calls for its replacement with more effective treatments.

Objective and Methods

The study aimed to assess the level of resistance to benzimidazole, a commonly-used drug for treating equine cyathostomins, more commonly known as “small strongyles,” in horses living in different zones of Uttar Pradesh, India. Researchers employed two techniques to identify benzimidazole resistance:

• The Faecal Egg Count Reduction Test (FECRT), which measures the number of parasite eggs present in a horse’s feces before and after treatment with benzimidazole.
• Allele-Specific Polymerase Chain Reaction (AS-PCR), intended to recognize a particular genetic mutation (F200Y mutation of the isotype 1 β-tubulin gene) associated with drug resistance.

Results

The researchers found widespread resistance to benzimidazole among the equine cyathostomin population. This pattern was particularly pronounced in horses from an intensively managed farm in the mid-western plain and three locations in central plains, where post-treatment larval cultures revealed the presence of exclusively cyathostomin larvae.

• The FECR (Faecal Egg Count Reduction) ranged between 27.5% on the intensively managed farm and between 75.7% – 83.6% in the working horses from central plains, indicating a high level of benzimidazole resistance.
• Genotyping revealed a high frequency of resistant (rr) individuals and the resistant allele in these areas. Importantly, the resistant allele frequency was notably higher in specific regions (Vindhyan and Tarai and Bhabar zones) of Uttar Pradesh.

Implications

The resistance level was significantly higher in the parasites of intensively managed horses compared to extensively managed horses. This finding suggests that certain practices associated with intensive management might contribute to increased drug resistance.

• The high prevalence of the resistant allele in the equine cyathostomins of Uttar Pradesh serves as a cause of concern and highlights the impending need to replace benzimidazole and similar drugs with alternate effective anthelmintics.
• The researchers emphasized the need for other, unrelated, effective treatments for the management and prevention of equine cyathostomins given the widespread resistance to benzimidazole.