CPD article: Equine gastrointestinal parasite infections

As grazing animals, horses can be infected by a wide range of gastrointestinal parasites including roundworms, tapeworms and bots. Horses grazing on pasture will be repeatedly exposed to these infections and even horses kept indoors without access to grass may be exposed to intestinal roundworm infection. As a result, the monitoring, treatment and reduction of parasite burdens in horses is a vital part of equine preventative health care. Successful parasite management in horses requires cooperation between veterinary professionals, stable managers and owners. Several parasites need to be considered. This article will discuss the parasites, diagnosis and treatment for each.

Infections with small strongyles is common, with horses becoming infected on pasture through the uptake of infective third-stage larvae (L3). The larvae then develop in the intestinal mucosa before they re-enter the intestinal lumen. Infections in horses kept indoors are rare and when they do occur, red worms are not present in sufficient numbers to cause clinical disease. Small burdens are generally well tolerated but large numbers of red worms can damage the intestinal mucosa and result in emaciation, diarrhoea and colic. When large numbers of larvae lie dormant in the mucosa then larval cyathostominosis can occur, a syndrome in which synchronised remergence of numerous L3 larvae results in massive tissue destruction. This disease is mostly seen in animals up to 6 years of age, and results in acute and persistent diarrhoea, which is sometimes accompanied by colic, weight loss or fever. Death is oft en the result.