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 public.

h142.jpg (21408 bytes)

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 "back" button of your browser to return to this page.

Clinical signs - prepatent disease





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