Clinical and Parasitological Evaluation of Ivermectin and Ivermectin + Pyrantel Against Oxyuris Equi in Equines.
Authors: Rodrigues Vinícius D, de Freitas Mariana G, Milan Bruno, Reckziegel Guilherme H, Borges Dyego G L, Nakatani Matheus T M, Tutija Juliane F, Borges Fernando de A
Journal: Journal of equine veterinary science
Summary
# Clinical and Parasitological Evaluation of Ivermectin and Ivermectin + Pyrantel Against Oxyuris Equi in Equines Pinworm (*Oxyuris equi*) control is becoming increasingly challenging, with emerging reports of treatment failures that prompted this Brazilian research team to compare the efficacy of ivermectin monotherapy against a combination formulation. Thirteen parasitologically confirmed cases were treated with oral ivermectin alone (200 µg/kg), and animals in which eggs reappeared before the pre-patent period were retreated with ivermectin plus pyrantel pamoate (6.6 mg/kg); therapeutic efficacy, clinical signs and egg reappearance periods were systematically monitored. The combination achieved 100% therapeutic efficacy versus only 53.84% for ivermectin monotherapy, with egg reappearance periods of 77.55 days and 50 days respectively—both shorter than the expected pre-patent period of 84 days, indicating incomplete larval elimination and early recrudescence. Animals receiving combination therapy showed greater clinical improvement at 30 days, with ivermectin-treated horses being 4.5 times more likely to display clinical signs at the same timepoint, and a significant negative correlation existed between egg reappearance timing and clinical persistence in the monotherapy group. These findings suggest that practitioners dealing with suspected pinworm treatment failures should consider combination therapy with pyrantel, particularly where clinical signs persist or recur despite standard ivermectin dosing.
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Practical Takeaways
- •Consider ivermectin + pyrantel pamoate combination for better control of equine pinworms; single ivermectin treatment shows inadequate efficacy in this population
- •Monitor treated horses closely beyond day 30, as egg reappearance occurs well before expected (50-77 days), potentially requiring earlier retreatment protocols
- •Clinical signs (pruritus, weight loss, irritability) are reliable indicators of active pinworm infection and should prompt parasitological confirmation and treatment adjustment
Key Findings
- •Ivermectin + pyrantel pamoate combination achieved 100% therapeutic efficacy compared to 53.84% with ivermectin alone
- •Egg reappearance period was shorter than pre-patent period for both treatments (77.55 days with combination, 50 days with ivermectin alone), indicating potential early reinfection
- •Animals treated with ivermectin alone were 4.5-fold more likely to present clinical signs 30 days post-treatment than those receiving the combination therapy
- •Presence of egg mass was always associated with at least one clinical sign, demonstrating direct correlation between parasitological and clinical findings