Prevalence of anthelmintic resistant cyathostomes on horse farms.

The article investigates the growing prevalence of anthelmintic resistance (resistance to deworming drugs) in cyathostomes, a type of parasitic worm, found in horses across the southern United States.

Research Methodology

• The researchers conducted a cross-sectional study involving 786 horses spanning 44 farms and stables in five southern US states (Georgia, South Carolina, Florida, Kentucky, and Louisiana).
• Fecal egg count (FEC) reduction tests were conducted as part of the procedure. This test is used to measure the effectiveness of deworming treatments by determining the reduction in the number of worm eggs present in the horse’s feces following treatment.
• Horses on each farm received treatment with a formulation in oral paste of one of four different deworming drugs at their recommended dosages: fenbendazole, oxibendazole, pyrantel pamoate, and ivermectin.
• A mixed linear model was used to analyze the results, factoring in potential differences among the farms, states, ages of horses, treatments applied, and interaction between treatments and states.

Research Findings

• Using a conservative measure of resistance (less than 80% FEC reduction), the study found that 97.7% of farms had cyathostomes resistant to fenbendazole, none had ivermectin-resistant worms, 53.5% had oxibendazole-resistant worms, and 40.5% had pyrantel pamoate-resistant worms.
• Mean percentage reductions in FEC scores across farms were 24.8% for fenbendazole, 99.9% for ivermectin, 73.8% for oxibendazole, and 78.6% for pyrantel pamoate.
• The states’ pairwise contrasts for each treatment indicated that in almost all cases, there were no significant differences between states’ results.

Conclusion

• The researchers concluded that anthelmintic resistance, particularly in equine cyathostomes, is a growing issue, with their findings showing an increased prevalence compared to previous reports.
• The similarity of data from the five geographically and physiographically distinct states suggests that this drug resistance is likely not isolated but prevalent across the southern United States, and potentially nationwide.