National Farm and Facility Level Biosecurity User Guide for the Equine Sector
Annex 12: Important gastro-intestinal nematode parasites of horses in Canada

Important gastro-intestinal nematode parasites of horses Table Note 35
Parasite Transmission and disease in horse
Large strongyles (Strongylus vulgaris, S. edentatus, S. equinus and Triodontophorus) Eggs shed in manure and develop into larvae in environment. Horses infected by eating larvae on pasture or in bedding. Larvae migrate through abdominal arteries and into other organs.
Horses appear unthrifty and weak, may cause diarrhea, weight loss, colic and bleeding.
Small strongyles (Cyathostomes – many species). Eggs shed in manure and develop into larvae. Horses infected by eating larvae on pasture or in bedding.
Larvae damage the intestine. Often few clinical signs. Weight loss if heavy burden.
Large roundworms (Parascaris equorum) Eggs shed in manure. Horses infected by eating eggs on pasture or in bedding. Larvae migrate through abdomen to lungs which are coughed up, swallowed and enter the intestine.
Respiratory or intestinal signs, unthrifty, weight loss, and colic.
Pinworms (Oxyuris equi) Eggs eaten off of hay or after contact with another horse. Eggs develop into worms in intestinal tract. Worms migrate out of rectum and deposit eggs near anus.
Causes irritation of area, itching and hair loss.
Lungworms (Dictyocaulus arnfieldi) More common in donkeys and mules. Eggs or larvae ingested on pasture, in bedding. Larvae migrate through intestine to lymph nodes and lungs where they mature to adult worms. Eggs from adult worms are coughed up, swallowed and enter intestine.
Irritation of lungs, coughing, difficulty breathing, can lead to pneumonia.
Tapeworms (Anopolocephalus magna, Anopolocephalus perfoliata and Paranoplocephala
mammillana)
Worm segments containing eggs shed in manure. Eggs eaten by pasture mites which are eaten by horses when grazing. Larvae develop in intestinal tract.
Can cause irritation of stomach, weight loss and colic.
Body cavity worms (Setaria equina) Adult worms in abdomen produce larvae which enter the blood and can be transmitted to mosquitoes. Larvae mature in mosquitoes and can be transferred to horses when mosquitoes feed. Occasionally adult worms migrate to lungs and infrequently to the eye. Migration to the eye can cause significant inflammation and lead to blindness.
Bots (Gasterophilus intestinalus) Flies lay eggs that stick to horse hair. Larvae develop and are ingested by horse.
Cause irritation to mouth and stomach.

Table Notes

Table Note 35

Bliss DH. The Control of Gastro-Intestinal Nematode Parasites in Horses with Emphasis on Reducing Environmental Contamination. "A New Control Strategy for an Old Problem." MidAmerica Ag Research, Verona, WI.

Return to table note 35  referrer

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