Identification of foals infected with Parascaris equorum apparently resistant to ivermectin.

The research article discusses the identification of young horses (foals) found to be infected with a parasitic worm (Parascaris equorum), showing the parasite’s strong resistance to the commonly used drug ivermectin.

Study Purpose and Approach

• The study aimed to identify any issues with the effectiveness of ivermectin in treating Parascaris equorum infections amongst a group of Thoroughbred foals in Ontario, Canada.
• These foals were subjected to routine fecal examinations, with the presence of P. equorum eggs indicating an active infection.
• After ivermectin treatment, the count of P. equorum eggs was repeated to determine the treatment’s effectiveness.

Findings

• From the initial group of 37 foals, P. equorum eggs were found in the feces of 9 foals.
• After administering ivermectin and conducting a second fecal test, P. equorum egg counts increased in 7 out of the 9 foals, remained unchanged in one, and decreased in five foals.
• In an additional group of 21 foals treated with ivermectin, P. equorum eggs were detected in 12 of them 13 days after treatment.

Conclusion

• The results suggested that the P. equorum parasites in these foals were resistant to ivermectin when administered at the recommended dosage.
• It was observed that high P. equorum egg counts following ivermectin treatment were more likely in those foals that had been regularly treated with ivermectin from birth and those permanently residing on the farm, compared with foals treated with other anthelmintics or with an unknown deworming history.
• The study thus indicates a potential issue in the widespread use of ivermectin as a treatment for this infection, suggesting the need for further research into alternative treatments and potential causes for this resistance.