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What? Equine sarcoids are skin tumours (usually benign) found on all equid species (horses, donkeys, mules, zebras and exotic asses). Although sarcoids are a type of skin cancer they are believed to not metastasise. They are usually identified by a vet by appearance, however the only definite way to tell is to do a biopsy. However biopsies are not usually taken as they tend to anger the sarcoid and can trigger it to grow at a faster rate, worsening it. Generally sarcoids are non-life threatening but they can be locally invasive and rarely regress.
Cause: Although no one is certain as to what causes equine sarcoids, it is widely believed that infection with Bovine Papilloma Virus (BPV) is responsible. BPV originated in cattle however it is unlikely that cattle play a large role anymore. Most horses will become infected with the virus however not all infections result in tumours. The appearance of tumours depend on the animal’s own immune system with between 2-8% of horses worldwide having the tumours. A widely accepted theory of transmittance is flies and it is believed that scar sites are more susceptible to the tumours.
Appearance: There are believed to be six different types of sarcoid; occult, verrucose, nodular, fibroplastic, malevolant and mixed. Sarcoids can be found on the back, tail, neck, around the eyes, on the face, eyelids, back and front legs and belly.
Occult sarcoids are flat and hairless with dry, crusty and dark patches. They are found on the inside of upper limbs, neck and eyes.
Verrucose sarcoids take on a wart-like appearance and can be ulcerated.
Nodular sarcoids are firm and nodular skin lumps. Many are covered by normal skin.
Fibroplastic sarcoids ulcerated, weeping, raised, sore skin lesions which may develop a ‘neck’ or stalk and become cauliflower-like. They are found in any area of the body.
Malevolant sarcoids are rare, invasive sarcoids, found as several nodules. They may invade deeper tissues beneath the skin.
Mixed sarcoids are combinations of different types of sarcoid.
- Cryosurgery: liquid nitrogen burns off the sarcoid. It works best on flat sarcoids.
- Banding with rubber rings: this works best if the sarcoid has a neck/stalk.
- Topical medication: the three types of topical medicines are ‘Aldara’ ‘XXterra’ and ‘Zorac’. ‘Aldara’ works as an immune response provider, XXterra contains an extract of Sanguinara canadensis and ‘Zorac’ is a retinoid that is also used for the treatment of psoriasis in people.
- Chemotherapy drugs: these can be administered as a cream or an injection.
- Surgical excision. This is often not advised as it can be difficult to remove all of the sarcoid and if part of it is not removed, it often becomes irritated and grows back worse than before.
- BCG vaccine: this is used against TB in humans. In equid species it can trigger their immune system to reject the sarcoid.
For tumours in the peri-orbital area, a new treatment is being used; high dose rate brachytherapy (HDRB). This does not have any significant acute adverse effects and results in a quicker recovery as the procedure is only a few minutes long. Additionally, as the horses are not radioactive, they do not need to be isolated.