Disclaimer: The following is only general information. If you believe that your horse has a problem please call your veterinarian as soon as possible.
A sarcoid is a skin tumour which is the most frequently diagnosed tumour in horses. Surveys have indicated that they account for 20% of all equine noeplasms (tumours) and 36% of all skin tumours. They can occur at any age and anywhere on the body, however they are more usually seen on the head, shoulders and lower limbs.
Sarcoids can be singular or multiple and of various types, which makes them one of the most mismanaged problems. The main problem arises when they are confused with other skin problems, as the treatment for sarcoids is different, for example, to the treatment for ringworm or warts or proud flesh at the site of an injury.
If your horse develops a lesion anywhere on its body (but particularly on its head, shoulders and lower limbs) seek help... do not treat it as trivial.
The six different types of sarcoids are:
Occult: These are flat, hairless, slightly crusty, dark patches which often have a smooth, dark, hairless area around them. These can be mistaken for ringworm.
Verrucose: These are raised, nobbly dark areas that often spread into poorly defined margins. They can also be ulcerated. May be confused with warts.
Nodular: These are firm, nodular skin lumps which may have normal skin over them. May be confused with cysts caused by insect bites.
Fibroblastic: These are often ulcerated, weeping, raised and sore lesions that may become cauliflower-like or pendulous when the tumour grows from a stalk. Some can be mistaken for proud flesh.
Mixed: It is not unusual to have two or three types of sarcoids at the same time.
Malevolent: Thankfully, these are rare as they invade deeper tissues beneath the skin.
The underlying cause of sarcoids seems to be the Bovine Papilloma virus, which is transmitted from cows to horses by flies.
Firstly, you should take all mystery skin lesions seriously as early treatment (while the sarcoid is small) will have a higher success rate. Your vet may biopsy the lesion to determine if it is in fact a sarcoid, rather than another skin condition, however this does not always give a clear result and can end up making the condition worse.
Currently, there are around 40 different treatments used worldwide, however none of them is 100% effective in curing this disease. The type of treatment will depend on the type of sarcoid, its location, how aggressive it is, clinical experience, owner's attitude, treatment cost, the horse's temperament, and the availability of services, equipment, and facilities in your area.
The one thing that most veterinarians agree on is that the treatment should be as aggressive as possible. Unfortunately, if 'softer' options are used initially and the sarcoid reappears, it usually does so in a more aggressive form.
Some of the most common evidence-based treatments are:
Surgical Removal: Although relatively easy to do it has a reoccurrence rate of anywhere between 15% to 82%, with most of the tumours growing back more aggressively within six months. Experts in the field recommend that surgery should always be coupled with another form of treatment.
Laser Removal: This has better results than surgical removal. This may be due to the fact that laser energy is absorbed by the surrounding tissue, therefore it kills the tumour cells up to 0.2mm beyond the wound margins. The downside is a fear that the procedure causes the infectious particles to become airborne, with unknown consequences to the horse or the surgery staff. Again, it is recommended that laser removal should be used at the same time as other treatment options.
Cryotherapy: This treatment involves freezing the tumour using liquid nitrogen, and although it is a cost-effective treatment it has had widely unpredictable results, ranging from 1% success to 100%, being reported. Another downside is the scarring and loss of hair colour at the site of the treatment. For this reason it is not considered to be appropriate for tumours near the eye, nostrils or similar structures.
Intratumoral Hyperthermia: This treatment uses heat to shrink or kill the sarcoid. The best results have been obtained when it is used in conjunction with chemotherapy (multiple drugs are given at or almost at the same time). Unfortunately, hypertherapy units are not commonly available in veterinary clinics.
Cisplatin Injections and Beads: Cisplatin is a chemotherapy drug, which can be administered by injection or beads. Injections are administered three to five times every two to three weeks at the site of the tumour. If the beads are used they are inserted into the tumour and the surrounding area where they can slowly deliver the drug over the next 30 days. Large sarcoids will need to be debulked (made smaller) before the injections or beads are used. This treatment has the highest success rate of 96.4%, with only a 3.6% recurrence rate.
Topical Acyclovir: Acyclovir is an anti-viral drug that has proved successful in shrinking large sarcoids so that cisplatin can be used. It also has a reasonable success rate (68%) with flat and mild-types of sarcoids. It needs to be applied every day for two to six months.
Topical Immiquimod: This drug is also used to shrink the tumour and has also had some success in resolving sarcoids that have already been reduced in size. The drug is applied every other day for 32 weeks, or longer if required. Some side effects include inflammation, oozing, loss of hair colour and hair loss.
Topical Blootroot Extract: This is a natural extract that results in cell death by burning. The salve must only be applied to the tumour and surrounding healthy tissue must be protected. The treatment is painful but economical with the sarcoid sloughing off in seven to ten days. Unfortunately, the treatment is usually required more than once. Bloodroot is marketed under the brand name Xxterra.
Bacillus Calmette-Guerin (BCG) Injections: BCG injections are used to stimulate the immune system. They have had good success around the eye region (83 – 100%), however the injections are not as successful for sarcoids on other parts of the body. BCG injections can cause severe inflammation, allergic reactions and anaphylaxis (life-threatening allergic reaction).
Autogenous Vaccine/Sarcoid Implantation: A vaccine is created using tissue from the horse's own body, or frozen pieces of sarcoid are implanted. Both treatments are trying to stimulate an immune response. To date these treatments have had mixed results.
Given that flies are the vectors that carry the virus from cows or other infected horses to an uninfected horse, the main preventative measures would be:
Minimise the fly population around horse facilities by good housekeeping (frequently removing manure) and installing fly traps (mechanical and chemical).
Use fly veils, fly sheets and fly sprays to minimise fly contact.
Cover any wounds with either a bandage or a product that seals the wound.
Take particular care of uninfected horses when they are in close proximity to infected horses during the fly season.