Large strongyles

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Large strongyles

Parasite Overview

There are three primary species of large strongyles that infect horses: Strongylus vulgaris, Strongylus endentatus and Strongylus equinus. Of the three types of large strongyles, S. vulgaris—the bloodworm—causes the most severe disease in horses. It burrows into the walls of arteries that supply blood to the small and large intestines, which can cause colic, tissue death, impaired intestinal function, twisting of the intestine, intussusception, bleeding and even intestinal rupture.

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Parasite Life Cycle

Adult strongyles produce eggs that exit the body in horse’s feces.
Eggs develop into infective larvae that live on pasture vegetation or in stalls.
Horse consumes grass, feed or water contaminated with infective larvae.
Larvae migrate through horse’s body.
Larvae become egg-laying adults in large intestine.

Clinical Signs

Fever
Decreased or absent gastrointestinal noises
Hyperemic mucous membranes
Normal to slightly elevated heart rate
No or mild pain
Negative gastric reflux
Sore mass palpable on rectal examination

Risk Factors

Age less than 3 years old
Contaminated environment
Environmental conditions conducive to egg and larval survival (mild temperatures)
Presence of “high egg shedder” horses in herd

Note: Widespread use of anthelmintics has made S. vulgaris much less common than it was 50 years ago.