Prevalence and clinical implications of anthelmintic resistance in cyathostomes of horses.

This research investigates how widespread, and what the implications are, of anthelmintic resistance in a type of parasitic worm (cyathostomes) that affect horses. The study found that some common treatments were less effective, but no resistance was detected to one drug, called ivermectin.

About the Study

• The study was set out to understand the prevalence and clinical implications of drug resistance in cyathostomes, a specific type of parasitic worm that burdens horses, to common anthelmintic treatments.
• In this prospective research, 80 horses from 10 different farms in northeast Georgia were studied. The researchers used three common anthelmintic drugs: pyrantel pamoate, fenbendazole, and ivermectin, alongside a control group that received no treatment.
• The horses were classified in a descending order based on their pre-treatment fecal egg count (FEC), divided into groups of 4, and then randomly allocated to one of the four treatment groups.
• To determine the effectiveness of each drug, fecal samples were taken 24 hours before treatment and then at 2, 4, and 6 weeks after treatment to calculate the FEC. The mean percentage reduction in FEC was then determined for each treatment group.

Findings of the Study

• The findings of the study indicated that resistance to fenbendazole was highly prevalent as it was ineffective at reducing FEC in horses from 9 out of 10 farms. Similarly, resistance to pyrantel pamoate was evident in horses from 2 farms, raising concerns about its efficacy.
• On the other hand, ivermectin was found to be effective in reducing FEC in horses from all 10 farms. This suggests there was no detected resistance to ivermectin among the studied population.
• However, the researchers caution that there was a small sample size in this study and the complete prevalence of cyathostome resistance to ivermectin couldn’t be accurately determined. Therefore, the efficacy of ivermectin should continue to be monitored closely.

Implications and Conclusions

• Resistance to anthelmintic treatment in cyathostomes of horses appears to be an emerging concern. The effectiveness of fenbendazole and pyrantel pamoate was found to be compromised due to resistance.
• However, ivermectin remains fully effective in treating horses affected by these parasites. The study emphasises a need for continuous monitoring to detect any potential emergence of ivermectin resistance in the future.
• In light of these findings, a periodic review of anthelmintic treatment strategies might be necessary to ensure effective controlling of the parasites in horses.