Large Strongyles in Horses
Strongyles are a strain of nematode worm that affect horses,particularly young horses or those that haven’t been exposed to parasites before. The parasite’s eggs can be found in the faeces of infected horses, with an infected animal passing 75-100 million eggs daily! Unlike many other parasitic life-cycles these eggs then hatch in to larvae on the pasture. The larvae go through a series of three molts and at the third stage can infect a horse. This can take around 1-2 weeks. These third stage larvae can live up to three months. They can be found at the tip of blades of grass, ready and waiting for a grazing horse to ingest them.
Each species of worm has a slightly different life-cycle and migration pattern. The Stongylus vulgaris is particularly interesting. Once ingested the larvae migrate to the large intestine where they shed their sheath and penetrate the intestinal wall. No matter where in the wall they penetrate, the larvae always end up in the same spot – the ‘root of mesentery’ with the horse’s abdominal cavity. This is where the cranial mesenteric artery, the artery that branches off to supply the entire midgut, originates. The congregation of larvae in this one spot causes potentially fatal damage to this artery. In rare cases the artery can rupture causing a rapid death, whereas in other cases they cause weakening of the arterial wall which can result in aneurism. An aneurism means a malformed artery, appearing as a balloon-like bulge in the vessel. This in turn causes disrupted blood flow and therefore the development of clusters of blood clots. If these loosen, break off and enter the blood stream they can block blood flow to the intestines, causing colic known as ‘thromboembolic colic’.
To diagnose a horse with these parasites it is easy to check for eggs in the faeces.
Worm your horses guys!