More than 40 different species of parasites that commonly infect horses are grouped under the term "small strongyles." These and another type of strongyle parasite, large strongyle worms, most often will infect a horse simultaneously. However, horses tend to be burdened by greater quantities of small strongyles, which also produce more eggs than the large strongyle worms.
Small strongyle larvae pose a significant health risk because they feed on the superficial lining of the large intestines, or the mucosa, where they cause damage that leads to the formation of ulcers, as well as severe inflammation of the cecum and colon. Larvae will migrate inside the intestinal wall and continue to develop into an adult, and live there within the mucosa in a dormant stage for an extended period of time.
Typically during the late winter and spring months, the small strongyles migrate out of the intestinal wall into the center of the intestines, and this massive movement of worms causes clinical signs such as diarrhea and colic. Severely affected horses and ponies may die from a small strongyle infection.
