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Strongyloides sp in Horses

By Thomas R. Klei, PhD, Boyd Professor and Associate Dean for Research and Advanced Studies, School of Veterinary Medicine and Louisiana Agriculture Experiment Station, Louisiana State University

Strongyloides westeri is found in the small intestine in foals. Adult horses rarely harbor patent infections, but mares often have larval stages within their tissues that are activated by parturition to move into the mammary tissue and, subsequently, are transmitted to foals in the milk. However, the relationship of S westeri infection with diarrhea in foals from 10 days of age has not been clearly established. The life cycle of the worm in horses is not known to differ significantly from that of Strongyloides in pigs (see Gastrointestinal Parasites of Pigs). Diagnosis can be made based on observation of eggs somewhat more oval and about one-third the length of strongyle eggs that contain larvae. Ivermectin and oxibendazole effectively remove S westeri. Transmission of larvae to foals via mare’s milk may be prevented by routine treatment of mares with ivermectin within 24 hr after foaling.