Strongylus equinus and Strongylus edentatus

Pathogenesis of migrating stages

Migrating larvae of Strongylus equinus and edentatus do not appear to cause pathological changes of enough severity to translate into recognizable clinical signs. However, migrations of larvae through the liver may produce nodules and formation of fibrous tissue that are readily seen at necropsies of infected horses.

The early migrations of Strongylus equinus larvae into the intestinal mucosa produce hemorrhagic nodules that are easily recognized at necropsy or during abdominal surgery in horses with colic. Whether or not these nodules may themselves produce colic in horses is debatable. However, their presence certainly indicates recent infections and it is safe to assume that such horses will also be infected with other large and small strongyles and these  may be primary contributors to the observed signs of colic.

The life cycle of Strongylus edentatus includes migration to the flanks where immature adults and L4s may be found at necropsy enclosed in subperitoneal cysts.  Although these lesions  have no clinical significance, they do indicate the presence of strongyle infections and a poor parasite control program in the farm of origin.

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Abdominal surgery in a horse with chronic colic showing hemorrhagic nodules in the small intestine caused by larvae of Strongylus equinus
Image courtesy of Dr. William Donawick
Necropsy of a horse showing hemorrhagic nodules in the intestine due to migrating larvae of Strongylus equinus. Image courtesy of Merial Inc Cross section of a larvae of Strongylus edentatus in the liver of a foal 62 days post infection. Image courtesy of Dr. Harold Drudge and Hoechst Roussel

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Acute reaction in the liver of a foal 2 months after infection with Strongylus edentatus.  Image courtesy of  Dr. Harold Drudge and Hoechst Roussel. Extensive fibrosis in the liver of a foal 5 months after infection with Strongylus edentatus. Image courtesy of Dr. Harold Drudge and Hoechst Roussel. Strongylus edentatus - an immature adult dissected out of a subperitoneal cyst on the right flank.
Image courtesy of Merial Inc.




Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on January 24, 2000