Worms - Donna Paton

SMALL STRONGYLES (Strongyles spp.)

This worm is also known as the redworm. The new name for this species is Cyathostomes. Although very similar to the Large Strongyles they do not cause as much damage, as they do not migrate through blood vessels. They are the most common worms for horses of all ages, up to 95% of horses have them.

Redworms are usually 2.5cm long and are thin with tapered ends. They are red to brown in colour, and have a small mouth and sharp hooks, which are used for grasping and penetrating.

99% of the worm eggs are passed in manure. They take 12 to 24 hours in manure to hatch into larvae. The larvae then develop for seven to ten days, before crawling into grass where they are then eaten by a host. Some larvae enter the gut wall and form deep nodules or cysts, where they may remain for up to two years. Other larvae may burrow but not cause a tissue reaction. Only a few species attach and suck blood. Either worming or the intake of green pasture then triggers the larvae to move on to the large intestine.

The adult worms are found in the large intestine where they cause irritation, utilising blood and protein for themselves. They cause persistent diarrhoea and may sometimes cause colic.

Foals are the most susceptible. In young foals, usually around 6 to 12 weeks, they may stunt growth and cause persistent diarrhoea. The more common signs of infestation are high fever, depression, intermittent diarrhoea, constipation and colic. Colic is the best indicator of Strongyle infestation. The incidence of colic in a group of animals is also a good indicator of the effectiveness of the worm control program. In adult competition horses, infestation may cause poor performance.

LARGE STRONGYLE (Strongylus spp.)

These worms are also known as bloodworms, and are not to be confused with redworms (small strongyle). The bloodworm is considered the most dangerous internal parasite. Every horse has bloodworms, even though the symptoms may not be displayed. They can cause permanent damage. There are three species Strongyle vulgaris, Strongyle equinus and Strongyle endentatus.

Bloodworms are usually 5cm long and are thin with tapered ends. They are usually red to brown in colour. The Large Strongyle have very large mouths with sharp hooks, used for grasping and penetrating.

The adult female may lay up to 6,000 eggs per day. The eggs hatch in 12 to 24 hours in fresh manure and will develop into larvae within seven to ten days. Larvae may survive for up to 26 weeks on pasture before being ingested.

Strongylus vulgaris

This is the most harmful worm in the large strongyle family. Damage occurs from the immature larvae, which travel through blood vessels, located mainly near the gut and hindquarter region. They irritate the arterial wall causing the wall to thicken; this causes the formation of Thrombi. The Thrombi then break off and from clots, which block the blood supply to the bowl. The immature larvae also weaken the blood vessel walls. They also can restrict blood flow and even block the arteries. They travel in these arteries to the cranial mesenteric artery. Small numbers may even be found in the aorta and other arteries.

Adult worms live in the large intestine where they damage the lining as they burrow through it, to suck the blood from the small blood vessels underneath. They can cause blood loss and haemorrhages, when they detach and reattach. In the large intestine they use up precious nutrients that are vital for the horse.

Signs of infestation are high temperature, loss of appetite, loss of body condition, depression and colic. The larvae may also cause a cranial aneurism, which can rupture.

Strongylus equinus

Ingested larvae penetrate the colon forming nodules; they emerge from these 10 to 11 days. After penetrating into the liver; where they remain for six to seven weeks. They go back to whence they came and penetrate the pancreas. It takes four to five months to develop into adults. Once adults they attach themselves to the caecum as bloodsuckers.

Horses usually infected with these worms show signs of high temperature, colic depression and loss of body condition. They also cause the necrosis and hepatitis.

Strongylus edentatus

Slightly smaller than S. equinus, being 26 to 38mmm in length, it is found commonly in horses (along with S. vulgaris). These worms tend to erratic migrations and have been known to be found in the testes, kidney, the abdominal cavity and elsewhere.

The migrating pathway to the vulgaris is similar but the pathway of the larvae is different. The larvae invade the liver within two days, by travelling through the cecal veins from the caecum.

Horses generally suffer from a high temperature, depression, colic constipation and diarrhea. Illness and death can result in two weeks. Horses do not generally suffer unless infested with large numbers.

If anyone else would like more of this article e-mail me and I will send you the copy.

Donna P.