Equine tapewormsPhoto kindly provided by University of Liverpool Diagnosteq Lab

Most horses are exposed to tapeworm and they may become infected at any age. Light infection is common, and if limited, is unlikely to produce any clinical signs. In severe cases, infection can cause physical damage to the gastrointestinal tract resulting in the following clinical signs:

• Diarrhoea
• Dull Coat
• Poor Growth
• Intermittent Colic Episodes
• Poor performance
• General Lethargy
• Ulceration of the GI lining
• Colic
• Obstruction
• Rupture
• Anaemia
• Un-thriftiness

Diagnostics & Treatment of Tapeworm

We know from the tapeworm life cycle that when the tapeworm sheds its eggs they are dispersed in a segment of its body called the proglottid.

If the proglottid remains intact then no eggs will be found in the faeces in spite of the horse being infected. As a result, tapeworm eggs are rarely detected in faecal egg counts (FEC) even if the horse is infected.

ELISA Antibody Test

The ELISA antibody test can be utilised to check for tapeworm exposure. This test is convenient and simple to carry out as saliva samples can be utilised.

Tapeworm - treatment options and resistance

Source: Canter Guidelines

Large Strongyles (aka Large Redworms)There are three major species of Large Strongyles, which are Strongylus vulgaris, S edentates, and S equinus. Of these, the most common is Strongylus vulgaris.

Thankfully the large Redworm (Strongylus vulgaris) is no longer as common

The eggs are ingested by the horse and once hatched, they burrow into the walls of the gastrointestinal tract.

Migration through the blood vessels occurs, until mature, and can cause massive internal damage before they return to live in the intestinal wall. Large Strongyles are blood feeders and they ingest mucosal plugs as they move through the intestine. Anaemia can result from this blood loss.

Large strongyles- treatment options and resistance

Source: Canter Guidelines

(cyathostomes spp)

Cyathostomes spp infestation in small intestine

The most common worm is the Small Redworm (cyathostomin spp) which can lead to encysted small Redworm disease if untreated.

When ingested, the larvae burrow into the lining of the intestines. They either develop and re-emerge to continue the life cycle, or stay in a state of hibernation in the intestinal lining-hypobiosis.

Hypobiotic larvae can all emerge at once causing severe damage to the intestinal wall which can cause weight loss, diarrhoea, shock and death.

The Typical Life Cycle of Small Strongyles

1. The horse ingests grass which has stage L3 larvae on it.
2. The larvae enter the large intestinal mucosa. There it either undergoes hypobiosis (similar to hibernation) and emerges as L4 later or immediately emerge as L4. There is a high damage risk of large numbers of encysted L4 emerging from mucosa at same time
3. The L4 larvae develop and lay eggs
4. These eggs pass out in faeces
5. The eggs on the faeces develop first into L1, then into L2 and finally into L3 larvae
6. The larvae move onto the grass
7. The horse ingests grass and the cycle starts again

Small strongyles- treatment options and resistance

¹ Larvicidal efficacy of moxidectin ranges from about 20 to 70% against Early Third Stage Larvae (EL3s), and 50-80% against developing larvae (late L3s and mucosal L4s) (Nielsen, 2022).
Source: Canter Guidelines

(Dictyocaulus arnfieldi)

Lungworm can cause coughing and respiratory difficulty in horses, although they are relatively uncommon. Lungworm is more common in donkeys and risk increases when horses and donkeys graze together

Horses become infected by eating the worm larvae from the pasture. The larvae will then move to the lungs, where they become adult. These adults, living in the airways, can cause obstruction leading to coughing and breathlessness. The adults lay eggs which are coughed up and swallowed to then be passed out in the droppings; thus continuing the cycle.

Lungworm - treatment options and resistance

¹ Not all authorised products have this indication
Source: Canter Guidelines

(Oxyuris Equi)

Adult pinworm emerging to lay eggs

The pinworm lives in the large intestine and passes out of the anus to lay its eggs.

The pinworm is a grey/white worm with a long tail, which tapers to a point. While the male is significantly smaller, the female pinworm can reach up to 20cm in length.

Although pinworms live in the large intestine and colon, the adult worm emerges at night to lay eggs on the skin around the rump. After laying her eggs, the female pinworm will then return inside the rectum. A female pinworm can lay up to 60,000 eggs per day.

The pinworm can cause severe itching around the anus which can occasionally lead to self-trauma.

Pinworm - treatment options and resistance

Source: Canter Guidelines

Bot eggs

The bot (stomach worm) is not a worm but the larvae of Gasterophilus flies.

The adult horse bot fly emerges a during the summer or fall season. After the fly emerges from the pupa, it quickly finds a mate, lays the eggs on the horse's coat and, on grooming, the eggs make their way to the mouth where they hatch in mouth as larvae.

Over winter the larvae burrow into the stomach lining (where they spend 8-10 months) and are then passed out via the faeces and will hatch in the summer.

Heavy infestation may result in trauma and ulceration of the stomach lining.

Disease is also caused by the larvae in mouth. Larvae here create borrowing holes, which in turn become infected. The 3rd stage larvae are passed in the faeces and over winters to develop the following summer.

Infected horses can often show no signs, which is why treatment should be given over the winter months to kill them.

Bots - treatment options and resistance

Source: Canter Guidelines

Large Roundworms (ascarids)Photo kindly provided by University of Liverpool Diagnosteq Lab

Ascarids, (also known as roundworms) are parasites which are mainly a problem to foals. However, small numbers can also be carried by adults.

The adult worms are very large and can be up to 40cm in length. Once the larvae of this parasite are swallowed, they pass through the gut wall, via the liver to the lungs. Heavy infestations can cause coughing as the larvae travel through the lungs.

Adult worms can cause intestinal impaction. They pose a considerable threat to young horses and their developing immune systems, and they have to potential to kill by triggering colic. Even if a young horse escapes colic, a heavy ascarid burdened young horse will appear depressed and its normal growth will be affected.

The most common ascarid to infect horses is Parascaris equorum.The eggs laid by the large females pass out into pasture protected by a tough shell which equips them well for survival.  They can withstand drying conditions and even freezing; waiting for that moment when a passing horse ingests them with grass.

Large Roundworms - treatment options and resistance

Source: Canter Guidelines

In-Feed medication tips from Bimeda Equine, ao you & your horse can get back in the saddle.

meloxicam 20mg/ml

oxytocin 16.6 µg