Threadworm (Strongyloides westeri) is usually seen in young foals, as early as four days after birth, up to 6 months of age. The worms cause inflammation, edema, and erosion of the small intestinal lining, which can result in impairment of digestion and absorption of nutrients.
The primary medical problem of a strongyloides infection is diarrhea that may not respond to treatment. Poor growth and depression can also be present.
Treatment of mares with a dewormer effective against strongyloides within 24 hours of birth significantly reduces transmission of the parasite to foals. The infection can be diagnosed by a standard fecal flotation test.
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