The Large Strongyles
Clinical signs - patent infections
It is generally accepted that mucosal feeding adults of all three
Strongylus species can have significant effects on infected horses although there appear
not to be any clinical signs that can be specifically attributed to them.
|General clinical signs of pale mucous membranes, poor weight gains and
even weight loss combined with dull, staring coats are seen in horses infected with large
strongyles. However, these clinical signs are generally seen in most parasitic infections
of the g.i. tract. The "wormy horse" (as shown in the image on the right), is
generally a poor performer and poor looking, a description that is often described as
"unthrifty". Horses like this are now relatively uncommon in the United States
because of the wide use (some would say the overuse) of anthelmintics and the
acceptance of parasite control programs by veterinarians and the horse-owning
Image courtesy of Dr. Harold Drudge and Hoechst Roussel
These clinical signs are related to the feeding habits of
adult worms which grasp a piece of mucosa with their large mouths and digest it, a process
that produces considerable bleeding at the bite site and results in formation of an ulcer.
Necropsies show that there are many more ulcers than adult large strongyles in the cecum
and colon, a finding that suggests these worms feed, then move to a fresh site . It
also implies that their primary source of food is mucosal tissues and that blood is
ingested only as part of the mucosal meal. This means that the large strongyles are more
accurately described as mucosal feeders than blood suckers.
However, their method of feeding, which can reach deep into the muscularis
with significant damage to blood vessels, can produce significant blood loss and result in
a clinically apparent anemia. Radio-active isotope studies comparing infected with
worm-free foals have shown significant protein and red cell losses into the g.i. tracts of
infected animals. These findings are not surprising but give a pathophysiological
foundation for the clinical picture we see in patent infections with large strongyles.
Click here to see a picture (courtesy
of Merial Inc) of a feeding Strongylus edentatus adult but remember to use the
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Clinical signs - prepatent disease