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
|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
||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
|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
||Strongylus edentatus - an
immature adult dissected out of a subperitoneal cyst on the right flank.
Image courtesy of Merial Inc.