Macrocyclic lactone-resistant Parascaris equorum on stud farms in Canada and effectiveness of fenbendazole and pyrantel pamoate.

This research aims to identify resistance in a common equine parasite, Parascaris equorum, to two drugs, and confirm the effectiveness of two others. The study found that the parasite showed resistance to ivermectin and moxidectin, but responded well to fenbendazole and pyrantel pamoate.

Study Objective and Methodology

• The study was conducted in 2002 and 2003 on three farms, focusing on 76 foals naturally infected with Parascaris equorum, a common equine parasite.
• The researchers aimed to determine if the parasite was resistant to ivermectin and moxidectin, two commonly used medicines for treating the parasite.
• Additionally, they wanted to confirm the effectiveness of two other drugs, fenbendazole and pyrantel pamoate, in treating the infection caused by the parasite.
• The trials were conducted on two Thoroughbred and one Standardbred farms in southwestern Ontario, Canada.
• Fecal Egg Count Reduction Test was used to estimate the number of Parascaris eggs per gram of feces for each foal pre- and post-treatment.

Treatment Plan and Process

• For each trial, the foals were randomly divided into treatment groups.
• The treatment included the four drugs under investigation, administered at the manufacturers’ recommended dosages, with some foals left untreated to serve as controls.
• After treatment, the researchers again conducted a Fecal Egg Count Reduction Test to measure the parasite’s response to the drugs.

Results and Conclusions

• The study found that the overall effectiveness of ivermectin was 33.5% and for moxidectin it was 47.2% indicating the parasite’s resistance to these drugs.
• In comparison, both fenbendazole and pyrantel pamoate showed a high rate of effectiveness against the parasite, each at 97.6%, demonstrating that these drugs are still viable treatment options.

These findings underline the need for continuous research and monitoring of drug effectiveness and resistance in parasites, in order to maintain effective treatment plans for equine health.