The following specimens were incidentally found during necropsy in the colon of a horse from Oklahoma (Image 1).
Image 1: Nematode found at necropsy
Images 2-4: Asymmetrical eggs, pointed tail and esophageal bulb
Oxyuris equi, are the pinworm parasites found in the colon of horses. Gravid females measure 4 to 15 cm. They migrate down the colon to the rectum through the anus to cement the eggs in the surrounding anal skin. The egg masses are a yellowish fluid with thousands of eggs. The fluid and egg masses dry out causing pruritus and contaminating fomites as well as the environment where the eggs become infective. Eggs are asymmetrical with a single polar plug (Image 2). Adults have a pointed tail (image 3) and an esophageal bulb (Image 4).
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