Strongyloides westeri is a parasite that has been associated with diarrhea in nursing foals approximately 10 to 14 days old.
When a foal nurses from an infected mare, parasite larvae are passed from mother to foal in the milk. In about two weeks the larvae mature and produce eggs that the foal passes into its feces, sometimes as diarrhea. Foals infected with this parasite are usually only minimally affected, and develop a resistance as they age. Grown horses usually have no symptoms of infection.
In order to treat the disease, worming medications are given to both mare and foal. Foals should receive immediate veterinary medical attention if they have diarrhea accompanied by sickness and dehydration, or develop diarrhea while they are not nursing. In these cases, Strongyloides westeri is probably not the underlying cause of the symptoms.
