Colic that requires surgery
The story of the large redworm was first discovered by researchers at Glasgow University. They established that when the larvae (immature stages) of this parasite reach the large intestine of the horse, they migrate through the gut wall. The migratory route is then along the arteries of the intestine to a site where the major intestinal artery branches off from the aorta. Here the larvae congregate in the wall of the artery, thus damaging the normally smooth wall and causing blood clots to form.
These clots can, at some time in the future, dislodge and travel down the artery until they become stuck in a small branch. When this happens the gut, which should receive blood from the blocked artery, becomes starved of oxygen. If this situation is prolonged for more than a few minutes the gut wall begins to die. This is painful for the horse and also causes leakage of potentially fatal bacteria and toxins into the abdominal cavity.
Tapeworms can be the cause of a very specific obstruction of the gut, impaction of the ileum (the last three feet of small intestine) at the point where it joins the large colon.
This type of colic problem has to be corrected surgically. Research using the tapeworm antibody test has demonstrated that horses with high levels of infection are up to twenty times more likely to suffer this type of colic.
A further colic problem related to worms is that of “intussusception.” This is a technical term describing a situation where one piece of gut telescopes into an adjacent piece of gut.
Both small redworms and tapeworms have been implicated in this condition which most frequently occurs around the caecum. This problem has to be corrected surgically, and only then with considerable difficulty.