Strongyloides westeri (Threadworm)

What you need to know

Infection occurs by eating larvae or through the skin. Larvae that enter through the skin migrate to the lungs, then up the wind pipe where they are coughed up and swallowed. Larvae mature into adults in the small intestine. Adults lay eggs that are passed in the dung. Threadworm larvae in the lungs can cause bleeding and respiratory problems. The worst damage often occurs in untreated foals who can suffer diarrhoea, weakness, weight loss and poor growth.

Effective wormer chemicals; Ivermectin, Oxibendazole.

More information

Strongyloides westeri is found in the small intestine in foals. Adult horses rarely harbour 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 diarrhoea 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 ( Strongyloides sp , Strongyloides sp). Diagnosis can be made based on observation of eggs somewhat more oval and about one-third the length of strongyle eggs that contain larvae. Transmission of larvae to foals in mare's milk may be prevented by routine treatment of mares with ivermectin within 24 hr postpartum.