Comparative use of faecal egg count reduction test, egg hatch assay and beta-tubulin codon 200 genotyping in small strongyles (cyathostominae) before and after benzimidazole treatment.

This research examines benzimidazole resistance in small strongyles (a type of parasite) in horses, using three techniques; faecal egg count reduction test, egg hatch assay and DNA testing of beta-tubulin genes. Results from three different farms indicate varying levels of drug resistance.

Introduction

• The study was aimed at evaluating the resistance of a type of horse parasite, small strongyles, against benzimidazole (BZ), a common anthelmintic drug. The research was carried out on three farms located in the tenth region of Chile.

Methodology

• The study used samples from a total of hundred horses and measured BZ resistance using three different methods. One method is the faecal egg count reduction test (FECRT), which measures the amount of parasite eggs in the animal’s faeces before and after drug treatment.
• Another testing method used was the egg hatch assay (EHA) that checks how well the eggs of the parasites can hatch after exposure to the drug.
• The third method was an allele-specific PCR, a type of genetic testing, for detecting beta-tubulin genes, which are heavily involved in BZ resistance. More specifically, the study looked for the presence of beta-tubulin isotype 1 genes coding for phenylalanine (phe) or tyrosine (tyr) at codon 200. These represent genetic markers of BZ resistance.

Observations and Data

• Resistance to BZ was found at all three farm sites, albeit to varying degrees. Farms located in Valdivia and Riñihue showed a higher degree of resistance than the third farm in Frutillar.
• Genotyping was performed on over 1700 single larvae from both pre- and post-treatment samples. While there was a general trend towards higher percentages of resistance-associated genotypes (phe/tyr and tyr/tyr) after treatment, the study did not find a statistically significant difference for the phe/phe genotype percentages.

Significant Findings

• A significant negative correlation was observed between the LD(50) values and the phe/phe percentages, and a positive correlation between the FECRT results and the phe/phe percentages, indicating a potential difference in the significance of the codon 200 polymorphism in BZ resistance mechanisms.

Conclusion

• The study results suggest the existence of BZ resistance among small strongyles in horses. While all three testing methods showed the presence of resistance to some degree, the observations indicate that the mechanisms of resistance may differ from those seen in other parasites, namely sheep trichostrongyles.