Equine sarcoid - everything you need to know about the skin tumor in horses!

What is a sarcoid in horses?

Equine sarcoid is the most common skin tumor in horses, with 2 to 8 % of all equines suffering from some form of sarcoid. In addition to horses and donkeys, mules and zebras can also be affected. Equine s arcoid is a benign skin tumor that can occur singly (solitary) or in several places (multiple). However, it does not form metastases, i.e. it does not attack any internal organs; instead, it proliferates into the surrounding tissue.

Experts describe a combination of several factors as triggers, with the bovine papillomavirus being described in combination with skin injuries, a weak immune system and poor hygiene.

Sarcoids are not fatal in horses, but can massively impair their well-being. Sarcoids are therefore not just a cosmetic problem: They are a skin cancer in horses that must be treated by a vet.

Equine sarcoid should not be confused with sarcoidosis, an inflammation that also spreads to the internal organs such as the lungs.

Causes: How or why does a sarcoid develop?

There are still many unanswered questions about the exact causes of equine sarcoid. However, experts are certain that the trigger is multifactorial and that the bulging skin tumor in horses is caused by a combination of different factors. It is also clear that it can be triggered by a local infection with viruses. One of the main players here is the bovine papillomavirus - a virus that is actually known from cattle. However, for a horse to be susceptible to the virus or an infection with it, a number of other factors must be involved.

Favoring factors for sarcoids in horses can be:

• Genetic predisposition
• Small, inconspicuous skin lesions
• Insects such as flies, especially in summer
• A weak immune system
• Stress-inducing environmental factors, as stress lowers the immune system
• Metabolic disorders with overloaded liver and kidneys

A genetic predisposition in the susceptibility to papilloma viruses can be explained by the fact that sarcoids can occur more frequently in some breeding lines.

Furthermore, the papilloma viruses require an entry point, as they are skin cancer-causing viruses. Small, unnoticed injuries are the main stumbling block here. If flies then come into contact with the wound at high temperatures, they act as potential carriers of the viruses. Equine sarcoid cannot be transmitted directly from horse to horse. It needs so-called vectors, potential carriers. And flies and other insects are at the top of the list. As sarcoids often occur in areas that flies also prefer on horses, such as the face or the inner thigh area, it makes sense to identify flies as vectors. However, grooming equipment, saddle girths and saddle blankets that are used by several horses can also transmit the viruses between horses.

For this reason, fly protection is important in summer. 

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Symptoms - how do I recognize a sarcoid in a horse?

Sarcoids can behave very inconspicuously at first, so that they are not even noticed. Some skin changes also resemble mumps, which is why skin cancer is mistaken for this in its early stages. Horse owners also make the mistake of confusing it with warts relatively frequently. Distinguishing it from other skin diseases is not so easy, especially in the early stages of the disease. This makes it all the more important to take a closer look at even the smallest skin and coat changes, take them seriously and seek veterinary advice accordingly.

So how do you recognize whether a horse has a sarcoid?

Sarcoids occur most frequently in areas with thin skin and little fur, where moisture is added. These are the head areas such as eyes, nostrils, the mouth or the base of the ears or the genital region. In geldings and stallions, sarcoids also tend to develop on or in the hose. However, areas of the body where small injuries are easily overlooked and a lot of irritation occurs are also "sarcoid hotspots". These are mainly the armpits, the rump between the forelegs, the girth area or the inner thighs.

Skin changes and skin irritations such as redness or inflammation can be seen in these areas. As a result, the horse may also lose its coat in these areas. However, lumps, small or larger growths and swellings are also signs of sarcoids. Depending on the type of sarcoid, lumps can also develop along the lymphatic channels.

Some sarcoids release a secretion that further irritates the surrounding tissue. In summer, the secretion attracts flies and maggots, which must be avoided at all costs to prevent the sarcoid from spreading.

Appearance & forms of equine sarcoid

Sarcoids can look very different, which sometimes makes it difficult even for experts to distinguish sarcoids from other tumors, inflammations and infectious diseases. Especially in their early stages, they are so inconspicuous that they go unnoticed for a while. However, sarcoids grow, starting with small changes to the skin and coat and progressing to growths which, depending on their shape, can even hinder the horse's movement.

There are 6 known forms of equine sarcoid:

• Occult
• Verrucous
• Nodular
• Fibroblastic
• Mixed
• Malevolent

There are mild and aggressive forms, whereby a mild, benign sarcoid can also change into an aggressive form - either for no apparent reason or through irritation and manipulation. It is therefore imperative that sarcoids are treated by a vet.

Occult sarcoid (concealed)

If a sarcoid is occult, it remains covered and inconspicuous, especially at first. It can only be recognized on flat, hairless areas, the surface of which may also appear scaly. It mainly affects areas of the body with sparse hair. As this form of skin cancer in horses remains hidden and only develops slowly, it is easily confused with other skin problems.

Verrucous sarcoid (wart-like)

Verrucous sarcoids in horses are often confused with warts, as they have an equally lumpy and rough surface. In addition, unlike all other forms, they grow relatively slowly and are therefore not classified as particularly aggressive. Wart-like growths can nevertheless cover very large areas and restrict the horse's movement or well-being.

Nodular sarcoid (nodular)

Nodular sarcoids can be felt under the fur as firm, shifting lumps. They can occur individually (solitary) or in groups (multiple) and are usually a sign of a serious disease process. In white horses, nodular sarcoids are often confused with black skin cancer (melanoma).

Fibroblastic sarcoid (fiber-forming)

The large, fleshy and cauliflower-like growths of fibroblastic sarcoid are among the most aggressive forms of sarcoid in horses. The growths penetrate deep into the surrounding tissue, which is why they are difficult to remove. Inadequate treatment increases the risk of fibroblastic sarcoids recurring. They can also bleed easily and therefore represent a dangerous entry point for further infections.

Mixed form

Their varied occurrence makes the treatment of mixed sarcoids particularly difficult. Mixed forms usually consist of verrucous and fibroblastic sarcoids. Even undetected sarcoids that are not treated but continue to be irritated can develop into mixed forms.

Malevolent sarcoids (malignant)

Malignant sarcoids are the most aggressive form of sarcoids and require intensive treatment by a vet. Malignant sarcoids can not only damage the surrounding tissue, but also spread to the lymphatic system.

Clinical or biopsy - diagnosis of sarcoids in horses

As soon as you suspect a sarcoid, do not under any circumstances undertake a more detailed examination yourself. Any irritation promotes the proliferation of the sarcoid! You should also urgently refrain from experimenting on your own, such as smearing zinc ointment on the sarcoid to try to dry it out. Always leave the diagnosis to the vet and it is better to call him too early than not at all.

As even the slightest touch can stimulate the sarcoid to grow further, the veterinarian's diagnosis is usually made exclusively clinically, i.e. by looking at the appearance alone. A biopsy can provide reliable information about the shape of the sarcoid, which provides a basis for the treatment plan. However, the tissue sample can promote uncontrolled growth. In addition, the puncture site provides an excellent entry point for viruses and bacteria, which can lead to secondary infections.

Although sarcoids in horses are generally not fatal, early diagnosis can prevent them from spreading. Because remember: Sarcoids in horses are not a cosmetic problem, but a tumor disease worthy of treatment.

What to do with sarcoids in horses?

The first step is to make sure that the affected areas of skin are protected from further touching and irritation. Above all, the horse should not scratch or bite these areas. In summer, fly protection is also important.

There are over 40 approaches to treating sarcoids in horses. The choice depends on the shape of the sarcoid, its location, length and size - there is no universal therapy. Sometimes it may even be best to do nothing at all and let the horse's immune system do its work. The sarcoid will then fall off on its own. However, waiting and watching is not always enough to treat sarcoids. That is why we are presenting a selection of the most important forms of therapy for sarcoids in horses below.

Surgery

In cancer therapy - sarcoids are a type of skin cancer - there are three pillars: Surgery, chemotherapy and radiotherapy. 

Surgical intervention is only an option in the treatment of an equine sarcoid if a safe distance can be established between the sarcoid and the skin tissue. It must be a well-defined lump. Otherwise there is a risk that the sarcoid will not be completely removed or that tumor cells will be "carried over" and the cancer will return elsewhere. Therefore, when surgically removing the sarcoid, 2 cm of surrounding healthy tissue must also be removed. Nevertheless, there is always the possibility that the horse's skin cancer will return after this procedure. There are therefore other forms of surgical therapy that can be a useful addition:

• Laser therapy: there is only a small risk of tumor cells being "carried over" and the sarcoid becoming established elsewhere
• Electrosurgery
• Cryosurgery: Tumor cells react extremely sensitively to strong temperature fluctuations, which is why the sarcoid is quickly frozen to -20°C and then thawed again

It is only possible to say with certainty whether the procedure was actually successful six months after the treatment. Unfortunately, skin cancer returns in around half of all cases.

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Chemotherapy

A sarcoid can also be treated locally with ointments or injections. Either the ointment is applied to the tumor or the drug is injected directly into the tumor. Both options are extremely lengthy, as they can only be repeated several weeks apart. In addition, the horse must be placed under short anesthesia for the injection.

Radiotherapy

Radiotherapy is often chosen for non-operable tumors. The radiation causes the tumor cells to stop dividing and thus spreading. In the long term, the sarcoid recedes and eventually falls off. Radiotherapy has a relatively high success rate in the treatment of sarcoids. However, the success rate decreases with the size of the tumor and the frequency of unsuccessful treatment attempts.

The horse must be placed under general anesthesia for radiotherapy in order to lie quietly in front of the radiation machine. This is precisely adjusted so that only the diseased tissue is irradiated.

All three forms of cancer therapy can be combined in the treatment of equine sarcoids to increase the chances of success.

Alternative forms of therapy for equine sarcoids

Alternatively, the vet can also prescribe ointments that can treat the tumor. Ointments containing thuja, mistletoe, sunflower, propolis, turmeric, bloodroot or cankerroot can be used for this purpose. The success of ointments depends on the size of the tumor.

Another option is immunotherapy: the horse's immune system is stimulated to defend itself against the tumor cells. This is done with either a bacterial vaccine or an autologous vaccine. The latter is obtained from parts of the tumor and is produced after around 10 days. Autologous vaccines can also be used for prophylaxis in whole groups of horses so that the horses are less susceptible to sarcoids. The sarcoid vaccine must be administered twice at intervals of approximately three weeks.

Influence of feeding and the immune system on equine sarcoid 

When fighting sarcoids, the horse's organism needs a strong immune system to deal with the tumor cells. This not only enables it to fight off the viruses that cause skin cancer, but also makes it easier for it to defend itself against the sarcoids that have developed.

The horse's immune system is weakened by various factors. On the one hand, stress plays a decisive role here. The hormone cortisol, which is released during stress, weakens the immune system and puts a strain on the metabolism. This is why horses with metabolic problems such as mauke, itching and obesity can often be affected by sarcoids. But digestive problems in horses such as watery stools and diarrhea are also indicators of a weak immune system, as many immune cells are produced in the intestines. If the horse has flatulence or watery stools, the intestinal flora is disturbed and therefore unable to produce sufficient immune cells. This makes the horse more susceptible to viruses such as bovine papillomaviruses, which cause sarcoid.

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This brings us to the next point: feeding horses with sarcoids. The sarcoid is not the actual problem that the horse is struggling with. Sarcoids are just the tip of the iceberg, the causes lie much deeper and are often due to an inadequate basic supply of nutrients. The first thing to look at is therefore the mineral supply: Is the horse supplied with all trace elements? Is the need for zinc, manganese and copper covered? Is the horse being fed a mineral feed whose nutrients are organically available?

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Any treatment of sarcoids should be accompanied by support for the detoxification organs liver and kidneys. A horse that is unable to break down harmful substances and detoxify its body will accumulate toxins in its body that will harm it in the long term. The liver and kidneys can be supported with dandelion, stinging nettle and milk thistle.

Finally, the intestinal flora should be maintained with the correct feed to improve the absorption of nutrients. A weak intestinal flora is not able to absorb nutrients from the feed - they are flushed out unused, which provokes a lack of trace elements. If the intestinal flora is already out of balance, it can be rebuilt with the help of feed charcoal and feed containing yeast fungi.

It goes without saying that the feed should be of consistently good quality. The toxins in the feed would only put additional strain on the entire organism and make the horse more susceptible to sarcoids.

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Prevention - can sarcoids be prevented in horses?

As the causes of sarcoids in horses still raise many questions, it is not possible to make any precise statements about prevention. What is certain, however, is that sarcoids are caused by a combination of different factors. In order to prevent them, high-quality feeding, good stable management and hygiene must be ensured. Each horse should only use its own grooming and saddlery. When grooming, pay attention to any changes in the skin and coat, especially in sensitive areas. And daily, free exercise to promote metabolism and digestion are also important factors in the prevention of sarcoids.

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Summary: The 11 basic rules of equine sarcoid

The 11 basic rules of equine sarcoid were drawn up by Professor Derek Knottenbelt, a professor of equine internal medicine. They can serve as a summary of the above points:

1. A sarcoid is a skin cancer, not a wart.
2. The majority of horses are susceptible to sarcoids, regardless of sex, coat color or breed, although certain breeding lines are particularly frequently affected.
3. Horses with a lesion (sarcoid) are particularly susceptible to recurrent sarcoids.
4. The more lesions the horse has, the more the sarcoid develops. It should therefore never be left untreated.
5. To put it very simply: sarcoids form in summer (flies that can transmit viruses) and grow in winter.
6. Sarcoids grow and become more aggressive over time; the larger they become, the more difficult they are to treat.
7. Any manipulation or intervention can lead to deterioration.
8. Any treatment of sarcoids is difficult and expensive. Every unsuccessful measure worsens the prognosis by 40 %.
9. There are 6 forms, which differ according to their clinical appearance and behavior.
10. Wounds to the skin, including wounds further away from the sarcoid, must be treated separately. A sarcoid can develop from any injury.
11. Sarcoids can also get better if left untreated: It is better to do nothing than the wrong thing.

FAQs - Frequently asked questions about equine sarcoid

Are there horses that are particularly frequently affected by sarcoids?

Around 2 to 8 % of all equidae worldwide are affected by sarcoids. Gender, horse breed and coat color do not seem to play a role. Sarcoids are most common in young horses aged between 3 and 6 years. However, any age group can be affected. Once a horse has had a skin cancer, there is a lifelong risk that the tumor will recur. With advancing age, the risk of a horse developing the disease (for the first time) eventually decreases, but is not completely eliminated.

Even if the breed does not appear to have a direct connection with the tumor disease, researchers were able to identify a frequency in certain breeding lines. In particular in the bloodlines of Quarter Horses, Appaloosas, Arabians and Thoroughbreds. A genetic predisposition to sarcoids is therefore suspected.

Are sarcoids contagious in horses?

How exactly sarcoids are transmitted or triggered has not yet been sufficiently clarified. Therefore, many questions remain unanswered regarding the risk of infection. Infection via the bovine papillomavirus, which is mainly found in cattle, is extremely likely. Whether infection with the virus occurs from cattle to cattle or from cattle to horse or from horse to horse remains an open question. Horses suffering from sarcoidosis should therefore be separated from the group to be on the safe side.

A further risk of infection can come from flying insects that carry infectious DNA. It has been found that sarcoids develop particularly in the summer months when there are lots of flies around, and then on areas of the body that flies like to fly to. Hygiene standards and insect defense therefore play an important role in preventing infection via papilloma viruses. Incidentally, these are very environmentally resistant and can remain on cleaning materials, skin flakes etc. for a long time, where they can survive without a host and remain infectious. 

Sarcoids are not contagious for humans.

How much does a sarcoid operation on a horse cost?

If a sarcoid has to be surgically removed, the cost of hospitalization can be high. Although there is the option of short anesthesia, this is not possible for the treatment of every sarcoid. The type and duration of the operation and therefore the cost of a sarcoid operation depend on the shape and size of the sarcoid. The supply of food in the clinic, wound care, preparations for the operation and the administration of medication also play a role in the costs. It is therefore not possible to generalize a cost range here. Nevertheless, you should expect a four-digit figure for a surgical procedure.

Are sarcoids painful for the horse?

In principle, sarcoids are not painful for the horse. However, depending on their size and extent, they can restrict the horse's movement and therefore its well-being. As sarcoids prefer to grow in areas of high irritation, such as the head, thigh or elbow area, they are particularly troublesome for the horse.

Sarcoids are also generally not dangerous or fatal for the horse, with the exception of malvolent, malignant sarcoids.

Can sarcoids recur?

There is a very high probability that sarcoids will recur once the horse has contracted them. Even a surgical, complete removal of the tumor is no guarantee that the horse can live the rest of its life free of sarcoids. Sarcoids are recurrent.