Sarcoids in horses

What are Sarcoids?

Sarcoids are the commonest tumour of the horse. They can occur at any age although most appear between two and ten years. The cause is believed to be a cattle wart virus but the way the virus induces the tumours is unknown. Files may play a key role in transmission, so fly control is vital to prevent spread.

Sarcoids are found:

  • In areas where the skin is thin, has little or no hair, and has a tendency to sweat. This includes the groin, the head and around the eyes. These are also areas where flies feed.
  • Rarely on the upper trunk, back and neck, unless the skin has been traumatised. The trauma may be slight, for example, bridle rubs on the face or rein rubs on the neck.
  • On the limbs, often at the sites of wounds where they may be mistaken for proud flesh.

Should I Buy A Horse With Sarcoids?

Because in principle they are treatable, it may be unreasonable to fail a horse with sarcoids at a pre-purchase veterinary examination. The vet’s advice will depend on the number, size, type and location of the sarcoids, and whether previous attempts at treatment have been made.

However, if they are detected at a pre-purchase examination, insurance companies will normally exclude sarcoids from cover.

Key Facts About Sarcoids

  • Some horses and breeds (Lipizzaner) are naturally resistant and will never develop sarcoids.
  • Sarcoids should never be underestimated. They have the potential to grow and spread, and be resistant to treatment. Every year many horses are humanely destroyed because of uncontrollable sarcoids.
  • A horse may have only a few to over a thousand sarcoids.
  • Some sarcoids remain quiescent for years, whereas others may grow, multiply and ulcerate.
  • A few horses self-cure but these are very uncommon.
  • Treatment must be intensive. Treatment failure often prompts the sarcoid to re-grow in a more aggressive (and more difficult to treat) fashion.
  • Even when successfully treated, new sarcoids may appear on a treated horse at any time.
  • The earlier treatment is started the more effective it is. It has been stated that ‘The fewer sarcoids a horse has, the fewer it will get‘.

Recognising Sarcoids – What To Look For

There are five main types of sarcoid, and a rare sixth very aggressive (malevolent) type.

Type 1: Occult

These are often very subtle in their early stages and may be just a hairless area with a slightly roughened surface. They are often circular and can look like ringworm.

Type 2: Verrucose

These have a roughened, warty appearance and occur especially inside the elbow and on the groin. In this horse the sarcoid has probably developed due to trauma to the site, perhaps as little as a fly bite.

Type 3: Nodular

Usually covered by normal skin, these hard nodules occur especially in the groin. These may be multiple sarcoids or just one. Sometimes the skin overlying the sarcoid ulcerates.

Type 4: Fibroblastic

The pink fleshy appearance of this sarcoid is typical. These are especially aggressive and fast-growing sarcoids. Treatment failure of sarcoid types 1-3 often results in the development of this type at the treatment site.

Type 5: Mixed

Often several types will occur on one horses.

Sarcoid Treatment In Horses

Consult your vet as soon as you suspect your horse may have a sarcoid. The vet will determine the most appropriate treatment. The options usually are:

Do nothing

Very flat, occult legions may be left untreated but must be watched carefully to ensure they are not transforming into another type.

Surgical excision

This is a good option for some nodular sarcoids but there is high rate of re-growth with other types.

Application of rubber ligature

This is best reserved for nodular sarcoids with little or no skin involvement. It is sometimes combined with injecting a cytotoxic drug into the sarcoid.

Freezing with liquid nitrogen

This is only moderately effective and there is a high rate of re-growth. It is only appropriate for very shallow tumours.

Injection of the human BCG vaccine

The vaccine is injected into the sarcoid and is very effective in sarcoids around the eyes but there is a risk of side effects.

Injection of anti-cancer drugs

This is effective in some cases but the drugs are difficult to obtain, require multiple treatments and there are safety risks to personnel.

Use of cytotoxic creams

Currently this is the best method, provided the appropriate strength of cream is used and treatment protocol is observed.

Radiation therapy

This is very effective but also very expensive. It is usually reserved for small sarcoids present around the eyes or over the joints where collateral damage to the adjacent structures (almost inevitable to a degree with the other treatment methods) is undesirable.

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