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Skin diseases
You can find more about horses here
Introduction
Dermatologic problems are common in horses. Even horses who receive the best of care may develop skin problems. There's just no avoiding the host of bacteria, fungi, viruses and insects that can lead to lumps and bumps, scurfy scabs, itchiness and hair loss. The owner sees a couple of scaly, crusty areas on his horse where the hair has fallen out. He has some sort of skin disease, but what? And what should you do?
Most people are afraid of ringworm, but there are a lot more diseases. Frequently a diagnosis can be made from an accurate history and careful physical exam. Occasionally tests may be need to be run to identify the cause of the disease. Most skin diseases clear up quicker with early diagnosis and correct treatment. To help you better understand the most common (and not so common) skin problems that affect horses, here’s a closer look at causes and cures. We make a differ between infectious, non-infectious and miscellaneous skin diseases:
• Dermatophytosis (ringworm)
• Dermatophilosis
• Folliculitis
• Sarcoids
• Warts
• Equine coital exanthema
• Mange (mites)
• Lice
• Sweet itch
• Ticks
• Bot flies (Gasterophilus intestinalis)
• Allergic contact dermatitis
• Urticaria (hives)
• Photosensitization (sunburn)
• Pastern dermatitis (mud fever)
• Nodular necrobiosis
• Skin tumors
• Cushing's disease
• Saddle eczema
• Vitiligo
• Albinism
• Pemphigus foliaceus
• Alopecia
INFECTIOUS SKIN DISEASES
• Dermatophytosis (ringworm)
Dermatophytosis is the most common skin disease in horses. The incubation period is 1-6 weeks.
Dermatophytosis in horse and in a child
Causes of ringworm
Ringworm is caused by various fungi (Microsporum and Trichophyton species) and is very contagious. Both are highly contagious for animal and owner (it's zoonotic)! Predisposing factors include age (young and aged), poor nutrition, stress and crowded conditions. The fungi can persist in the environment for up to one year and therefore are an important source for reinfection.
Horse-to-horse transmission is common, especially in groups of young horses or in sick horses that are immunosuppressed. Spread of the spores via infected tack, blankets, bedding, trailers or fencing can occur. It is rare for healthy horses to get ringworm more than once as usually a horse develops immunity after being infected.
Diagnosis
Diagnosis: The best way to diagnose this problem is by performing a fungal culture. This is accomplished by taking hair samples from the outside edge of a few of the lesions. The hair is then placed on fungal specific media and any dermatophytes are allowed to grow over a period of days.
Signs of ringworm The incubation period is 1-6 weeks, but sometimes shorter. Small hairless lesions that may be red and sometimes look like hives and scaly or crusty areas. Ringworm can affect any part of the body but lesions are usually found on the face, neck, chest, shoulder or on the girth area (known as girth itch). Lesions may or may not be itchy or painful. Symptoms in horses usually start with patches of raised hairs in a circular (ring) pattern. The lesions sometimes look like hives and scaly or crusty areas, typically located in the saddle, face and neck areas.The hairs give way easily when plucked and hair loss follows, leaving a silvery scaling of the underlying skin.
The lesions are mainly pruritic (itchy) in the early stages of the disease but can remain sensitive to the touch for longer periods. The initial ringworm lesions can spread outwards to cover large areas of the body, if no appropriate measures are taken.
A horse may carry fungal infection without any symptoms.
Treatment of ringworm
Ringworm is usually self-limiting, with the horse getting better in one to three months without treatment, but treatment is recommended because infected horses are the source of infection to other animals and people. Exposure to sunshine is thought to be beneficial. To shorten the course of the disease, affected horses can be treated topically with a wide variety of antifungal treatments, such as miconazole (Imaverol®), natamycin and nystatin.
Widespread lesions are best treated with antifungal rinses or dips, such as lime sulfur or even diluted vinegar. However, the fungal spores that have contaminated the stable environment and equipment may persist for years, thus enabling re-infection. Disinfecting the environment, tack and grooming equipment with diluted bleach or commercial antifungal premise sprays is extremely important.
Prevention
As no treatment actually shortens the healing time of ringworm, prevention is key in order to avoid an outbreak on a yard. Vaccinations are not yet widely available and the need for repeated boosters may not be practical or economical.
Maintaining hygienic work practices is key to preventing a ringworm outbreak on an equine yard. These practices help to minimise the chance of environmental contamination.
If an outbreak should occur then damage control will be mainly through the prevention of direct and indirect spread between horses.
• Dermatophilosis (rain rot, rain scald, rain rash, mud fever, cracked heels, scratches, greasy heel, mud rash, dew poisoning)
Rainrot
Rain rot is a bacterial infection aggravated by prolonged exposure to moisture coupled with injured skin. Chronically infected animals are the primary source of infection. Transmission can occur by flies, ticks, grooming equipment and tack. Once the disease has occurred within a barn or an individual horse, it is generally there to stay, just waiting for favorable weather conditions to reappear. In fact, any horse can be infected and once they have been, will often get it every year. Animals housed under poor conditions may be affected also.
Signs of rain rot
Lesions over the back and rump, although any area can be affected. The lower layer of hair is firmly matted in small scabs which, when plucked may leave a characteristic ovoid (egg-shaped) bleeding surface. The hairs are cemented together into characteristic 'paint-brush' clumps. The undersurface of the scab is concave with the roots of the hair protruding and may have a covering of yellowish-orange pus. The affected areas are mildly to severely painful, but are not itchy to the horse. Humans develop an exudative dermatitis similar to that seen in animals.
Other forms involve the pastern (mud fever).
Treatment of rainrot
Often resolves spontaneously after moving the horse to a dry environment. Also helpful in most cases is daily bathing with antimicrobial shampoos (chlorhexidine or povidone iodine) for the first week, then twice weekly until healed. Severe cases require oral or injectable antibiotics.
• Folliculitis (Staphylococcus aureus)
Staphylococcus aureus is a highly resistant bacterial infection. It is an inflammation of the hair follicles. When the inflammation spreads in the dermis and subcutis, this is called furunculosis. Most cases occur in the spring.
Signs of folliculitis
Warm painful skin, focal crusts, most commonly in the pastern region, but similar lesions elsewhere on the skin can occur. In some cases, the infection seems to rapidly involve deeper tissues. If allowed to become chronic, the underlying tissue can begin to scar and thicken.
Treatment of folliculitis
With the increasing resistance issues of certain bacteria, especially Staphylococcus, it is important to obtain a culture and sensitivity pattern to make sure that the correct antimicrobial agent is selected. Wash the infected with betadine (povidone iodine). Local treatment with antimicrobial ointmenst is not recommended: it will not penetrate deeply enough to be effective.
• Sarcoids
Sarcoids are the most common skin tumours of the horse. Some believe that sarcoids may be better considered as tumours as they seem to be not contagious. Thought to be viral in cause, sarcoids frequently occur in areas subject to trauma and may spread to other areas on the same horse or to other horses through biting, rubbing, fomites (inanimate objects such as tack, grooming tools, et cetera) or insects. They can be found in all breeds and at all ages.
Often the tumours are multiple and can be found everywhere on the body, but mostly on the groin, axilla, face, neck, ears, lips, eyelids and ventral abdomen.
Currently six different types of sarcoids are recognised. A single animal can have several different types at the same time.
Diagnosis
The pathological appearance is typical. Biopsy is possible but may also be dangerous.
Treatment
Because many equine sarcoids often recur after they are removed, treatment can be challenging. Often more than one of the following treatments are used on the same sarcoid:
• Cryosurgery.This method destroys the tumor by using extremely cold temperatures. Like surgical removal, cryotherapy is often combined with other techniques to achieve a better outcome.
• BCG-immunotherapy
• Surgical removal. Complete surgical removal of the tumor is often difficult and many sarcoids return. This method is often combined with some of the other techniques.
• Chemotherapy. This treatment requires special training on the use of chemotherapy for both the veterinarian and horse owner.
• Topical therapy
The prognosis of sarcoids is always guarded and is dependent on the size and the location of the tumours. They don't metastise but although they stay local therapy is not always successful and recurrence is quite possible.
Different types of sarcoids
• Warts
Warts on the nose and lips of a horse
Viral papillomatosis (warts) are also viral-induced tumors. It's relatively common in young horses (1-3 year of age), sometimes less than 1 year of age, kept in large groups. Warts are usually a self-limiting condition lasting 3 – 6 months, however warts are contagious to other horses sharing feeders and tack.
Signs
The infection with the virus occurs through little wounds or abrasions. Incubation period is 2-3 months. Small warts on the nose and lips.
Treatment
Spontaneous resolution usually within three months. Surgical excision or cryosurgery are effective if removal for cosmetic reasons is needed or if a wart is very extensive. Horses with many warts often have other diseases.
Prevention
When an animal has a wart infection, it should be isolated from other animals. Any infected animal should also be kept from rubbing on feeders and posts that may be used by other animals. Cleaning of equipment with a product like chlorhexidine is essential for preventing the spread of warts.
• Equine Coital Exanthema (Genital horsepox, Equine venereal balanitis in stallions)
This is a contagious benign venereal disease of horses that probably occurs worldwide. It affects both sexes and is caused by equine herpesvirus type 3 (EHV-3). The incubation period is 5-7 days.
Signs
Multiple, circular, red nodules up to 2 mm in diameter on the vulvar and vaginal mucosa, the clitoral sinus, and perineal skin. They may be mildly pruritic. These lesions develop into vesicles and then pustules and eventually rupture, leaving shallow, sometimes painful, ulcerated areas that may coalesce into larger lesions. Skin lesions persist for long periods as unpigmented scars. However, pregnancy rates are not reduced. Lesions in stallions are similar to those in mares and are found on both the penis and prepuce. As a result, intromission is painful, and the stallion may be reluctant to copulate.
Treatment
Sexual rest to allow ulcers to heal and prevent the spread of the disease. Use antibiotic ointments to prevent secondary infections
• Mites (mange)
Lice and mite (Chorioptes) infections are the most common parasitic skin infections in horses. Infections with Chorioptes are the most common mite infections in horses, while infections with Sarcoptes and Psoroptes are very rare. The are very contagious and may spreda through direct contact or indirect contact (tack, grooming material, etc.).
Chorioptis mange
Chorioptic mange is common in heavy breeds of horses and is most often identified in winter in horses with feathered fetlocks (Friesians, etc.). Lesions caused by Chorioptes equi start as a pruritic dermatitis affecting the distal limbs around the foot and fetlock. Papules are seen first, followed by alopecia, crusting, and thickening of the skin. Clinical signs are usually limited to the distal limbs, but sometimes the whole body can be affected. A moist dermatitis of the fetlock develops in chronic cases. The disease course is usually chronic without treatment, but the prognosis is favorable when treated. Diagnosis is made after microscopic examination of a skin sraping. Before treatment it's advisable to clip long hair. Topical treatments with anti-ectoparasitics are recommended. The whole horse should be washed. Amitraz is contra-indicated, because it's very toxic to horses: it can cause severe colic and death! Blankets, brushes, and ropes can be soaked in boiling water, while saddles and other leather items can be treated by wiping on a topical insecticide.
Administration of ivermectin or doramectin are also very effective. Repeat these treatments within 10-14 days, as the eggs are not killed by this treatment.
To control infestation on individual horses, a 0.25% fipronil solution (Frontline), the commonly used canine flea and tick control agent, can be used.
Left: Chorioptic mange in a Shire
Middle: Chorioptes mite
Right: close-up Psoroptes mite
Psoroptic mange
Psoroptic mange is very rare: it produces lesions on thickly haired regions of the body, such as under the forelock and mane, at the base of the tail, under the chin, between the hindlegs, and in the axillae. There is moderate to serious pruritus. Treatment: see Chorioptes.
Sarcoptic mange
Sarcoptic mange is also very rare but is the most severe type of mange in horses. Sarcoptes infections cause very intense pruritus, leading to severe automutilation and often secondary bacterial infections. Lesions start as small papules and vesicles that later develop into crusts. Alopecia and crusting spread, and the skin becomes lichenified, forming folds. If untreated, lesions may extend over the whole body, leading to emaciation, general weakness, and anorexia. Negative skin scrapings do not rule out the disease; biopsy may establish a diagnosis. If suspected, sarcoptic mange must be treated (see Chorioptes).
Demodectic mange
Demodex equi is rare in horses. The mites live in the hair follicles and sebaceous glands. This disease has been reported in association with immuno-suppression (stress, other diseases, chronic corticosteroid treatment, etc.). Demodicosis in horses can manifest as patchy alopecia and scaling, or as nodules. Lesions appear on the face, neck, shoulders, and forelimbs. There is no pruritus.
Severe Sarcoptes mange
• Lice (pediculosis).
Left: nits (eggs) of lice.
Right: Hamatopinus louse
Lice and mite (Chorioptes) infections are the most common parasitic skin infections in horses.
Lice infestations most commonly occur in late winter and early spring when the horse’s hair coat is at its longest and when horses are congregated together. There are sucking lice (Haematopinus) and biting lice (Damalinia). Lice occur predominantly in young or diseased animals.
Signs of parasatic infestations
Extreme pruritus. Additionally, horses troubled by lice often rub or bite at affected areas (usually the legs).
Diagnosis
The diagnosis is made with the naked eye (lice and nits can easily be seen) or after microscopic examination af a skin scraping.
Treatment for both problems
Treatment for both problems Includes topical anti-ectoparasitics, selenium sulfide shampoos, lime sulfur dips and oral dewormers, such as ivermectin. All in-contact horses and the environment must be treated. Horses should be retreated in about two weeks to kill young lice and nits that have just hatched and were not affected by the first treatment.
Ivermectin has a limited effect.
• Sweet itch (summer itch, culicoides hypersensivity, Queensland itch, Summer Seasonal Recurrent Dermatitis)
Sweet itch
Culicoides hypersensitivity is an allergic skin disease affecting susceptible horses and ponies (especially Welsh and Icelandic ponies and Friesian and Shire horses) that become hypersensitive to the bites of the insect of the genus Culicoides ('biting midges', 'punkies', 'no-see-ums'). The allergic reaction is caused by the saliva of the insect.
This very itchy, but not contagious disease is initially seen only in the warmer months, between March and October, during the early morning and the evening. As affected animals age, the disease generally becomes more severe and reactions can be seen year round. All horses are liable
Signs of sweet itch
Peeling skin, crusts, scaling, hair loss and redness primarily involving the forehead, crest of neck, withers, shoulders, rump, ventral midline and the base of the tail.
Diagnosis
The pathological appearance is typical
Treatment of sweet itch
The best treatment is, of course, avoidance of contact with the insects. Since culicoides are primarily night feeders, keep the horse inside from dusk to dawn. You can also use special suits or blankets. Fly spray repellent is a must. In severely affected horses, corticosteroids is usually necessary to control the itchiness. The symptoms immediately reappear when the horse is brougfht back to the pasture.
It is also a good precaution when buying horses in the winter to ask about skin problems that could have been a problem the previous summer. You can assume that a problem last year will most likely be a problem this year.
• Ticks
Ticks are found especially in areas with long grass. Usually ticks cause mild irritation at the site of the bite. Ticks transmit several serious diseases to both animals and humans, including Lyme disease. Most insecticides or anti-flea preparations will kill them. If pulled out, leaving the head in, an area of irritation van persist.
• Bot flies (Gasterophilus intestinalis)
Left: Eggs of the Horse bot fly on the hairs of a leg
Right: Gasterophilus larvae in the gastrointestinal mucosa
This is not really a skin disease, but the adult horse bot fly may cause fear in horses. The bot flies are about the size of house flies. There are three types of horse bot flies. The females deposit yellow eggs (sometimes black eggs) on the hairs of the chest, shoulder, (front) legs, belly and flank of horses and are difficult to remove from the hairs. In these eggs are larvae. They are licked by the horse and after that the life cycle in the horse starts. They migrate from the oral tissues to the stomach, where they attach to the lining to complete the larval growth stage. When that stage is complete, they detach and are passed out with the manure, where they pupate, and in time, emerge as adults.
Severe infestations of horse bots cause gastrointestinal stress, block the stomach outlet (causing colic) or rupture the stomach (causing death).
Treatment: use a suitable anti-parasiticum like ivermectin in the autumn or early winter.
NON-INFECTIOUS SKIN DISEASES
• Allergic contact dermatitis
Allergic contact dermatitis occurs when irritating substances come into direct contact with the skin of hypersensitive horses. Irritants vary, but can include bedding, fly sprays, shampoos, liniments, urine, etc.
Signs
Lesions occur in areas that come in contact with the offending substance and vary from mild redness, flaking and itching to severe hair loss, skin thickening, pain and occasionally skin sloughing. These swellings often "pit" when an indention is made in them with a finger.
Treatment
Remove the causative substance and wash the skin with copious amounts of water. Adds Dr. Sargent, “In severe cases, topical or systemic anti-inflammatories and antibiotics may be required.”
• Urticaria (hives, skin bumps)
Urticaria
This is a common, allergic response that can be caused by many things, including diet, infectious diseases (bacterial, fungal, viral and parasitic infections), stinging nettles (nettle rash), insect bites (sweet itch), chemicals (carbolic acid, turpentine or crude oil, etc.), medicines (especially to antibiotics and nonsteroidal anti-inflammatory drugs, the most common cause) and Inhaled allergies (pollens, molds, smoke, dust, plus others). Sunlight, heat, exercise, psychologic stress, and genetic abnormalities may precipitate or intensify urticaria. Often the cause is not clear but it occurs in all domestic animals but most often in horses.
Signs
The sudden appearance of hive-like lesions (weals or plaques), which can occur anywhere on the body and the upper limbs, but mainly on the back, the flanks, the eyelids and legs. The localized edemas result when the capillaries beneath the skin leak a clear fluid from the blood into the tissue spaces below the skin's surface. The lesions are elevated, round and flat-topped. They may or may not be itchy. Lesions typically last from a few hours to a few days. In severe cases, the cutaneous eruptions are preceded by fever, anorexia, or dullness. Horses often become excited and restless.
Treatment
Acute urticaria usually disappears spontaneously. Severe urticaria reactions can be treated with corticosteroids. Antihistaminic drugs have minor effect in horses and may even induce urticaria.
Prevention
Try and pinpoint what is actually causing the problem and of course avoid or eliminate it. Get rid of irritants in the field such as stinging nettles. Protect your horse from flies.
• Photosensitization (sunburn)
Photosensitization is an abnormal, inflammatory skin reaction to UV light that occurs in areas with white hair and non-pigmented skin, most often on the muzzle or bridge of the nose and the ears. Its is a systemic disease, and there are two forms of photosensitization: a primary form associated with eating certain medicines (tetracyclines) and plants (St. John’s Wort, oats, clover, vetch, alfalfa, et cetera), and a secondary form that occurs with liver disease.
Signs
The skin is characterized by redness, localized swelling, sensitivity to the touch and could have weeping of serum. In many instances there will be loss of skin. With secondary photosensitization, the horse will also be itchy.
Treatment
Primary photosensitization is treated by eliminating access to the offending plants and keeping the horse out of the sun. Topical antibiotic/steroid ointments are also beneficial. With secondary photosensitization, treatment is directed toward managing the liver problem. Stabling during the day may be necessary or applying products to protect against sunburn. Always test products on a small area of skin first to make sure it won't cause irritation itself.
• Pastern dermatitis (mud fever, greasy heal, scratches, cracked heels)
Left: Pastern dermatitis. Right: Choriptes mite
Pastern dermatitis is a syndrome caused by a variety of diseases (including bacterial infections, dermatophilosis, staphylocoocusfungal diseases such as ringworm, chorioptic mange, irritant contact reactions, photosensitization, trauma, neoplastic disorders, metabolic disorders, etc.) These causes can be diagnosed with skin scrapings, fungal cultures and skin biopsies. A variety of factors have been associated with the development of scratches: white hair on the lower limbs, trauma and insect bites, increased moisture or standing water, treated bedding, and poor stable or pasture hygiene. Horses with a lot of feathering on their legs, like Friesians and Shires, seem to be particularly susceptible.
Signs
Inflammation, swelling, open sores and foul-smelling crusts on the rear half of the pasterns and matted hair. The skin may become thickened and painful enough to cause lameness.
Treatment
If you ask ten horse folks about the treatment of scratches, you'll get ten different answers. Some seem to work and some don't.
Treat the underlying cause: avoiding pastures that have excessive mud or standing water, and keeping affected horses stalled during wet weather or until the morning dew has dried can be helpful.
Remove the scabs. Ointments generally can’t reach the bacteria causing scratches which hide safely underneath these scabs. Most scabs are removed without too much trouble when using lukewarm water and a mild shampoo like Betadine. Clipping hairs, especially feathers, can also help decrease moisture retention (Friesian-owners hate to hear this); remove the horse from unsanitary, wet conditions; and minimize contact with irritating chemicals, plants, et cetera. Clean the area, and apply shampoos, soaks, topical or systemic antibiotics and/or steroids per veterinary recommendation. Some people have good results with putting tooth paste on it...
In more severe cases or those that involve multiple legs, daily systemic antibiotics may be necessary.
Therapy of Chorioptic mites: see • Mange (mites)
Prognosis
Unfortunately, those horses that develop scratches tend to develop them again. Early identification and treatment is the best remedy.
• Nodular necrobiosis (equine collagenolytic granuloma, eosinophilic granuloma)
Nodular necrobiosis
This is one of the most common nodular skin disease in horses. You'll see one to several firm non-painful dermal nodules (0.2-1.2 inches, or 0.5-3.0 cm, wide) located in the deep skin layer, primarily on the withers, neck, and back, although they also can appear elsewhere. The hair over them is undamaged. There is usually no pain or itching. There are no known predisposing factors, nor is the cause known, although some sort of hypersensitivity reaction related to insect bites and mosquitoes is likely. Incidence is higher during the warm seasons due to higher insect activity. Treatment is usually not necessary because the nodules are frequently no more than a blemish. Horses with multiple lesions may be treated with corticosteroids.
• Skin tumors
Some common dermatological tumours can be diagnosed with a high degree of confidence by the experienced equine practitioner based on the presenting history and gross clinical signs. Where possible, a histopathological diagnosis should be sought for confirmation.
Left: Melanoma around the anus of a pony. Middle: melanoma under the ear. Right: Squamous cell carcinoma of the third eyelid
1. Squamous cell carcinoma is a malignant skin tumor of the outermost layer of the skin. Squamous cell carcinoma can develop in virtually any location in the integument. It’s primarily found in nonpigmented areas of the skin at mucocutaneous junctions such as eyelids, lips, nose, genital area and occasionally the mucous membranes.
Clinical signs
Reddened, roughened or ulcerated skin.
Treatment
Surgical removing of the tumor, chemotherapeutic drugs, cryosurgery (destruction of unwanted tissue by freezing), anti-inflammatory therapy or radiation therapy.
2. Equine ear papillomas (warts in the ear), Viral papillomatosis (warts) and Sarcoids are viral-induced skin tumors (see: infectious skin diseases above) are all viral skin diseases in the horse. Some believe that sarcoids may be better considered as tumours as they seem to be not contagious.
3. Melanoma is a common tumor in older horses and is seen more often in gray or white horses.
Clinical signs
Round, nodular or ulcerated slow-growing lumps underneath the tail, perianal region (anus, vulva); less commonly on the lips and base of the ears. Incidentally melanoma are found elsewhere. Usually the tumours ar benign but there are highly malignant cases and extensive metastases to the lymphnodes, liver, lungs, and spleen. Signs of malignancy include areas of pink tissue within the melanoma.
Treatment
This is often not possible. Surgical excision unless tumors are numerous. It seems that cimetidine (Tagamet®) is a potential treatment for equine melanoma. Equine melanocytic tumors treated with cimetidine for 1-12 monthes showed diverse responses in different experiments. In some cases the number and size of tumors decreased by 50-90% but in others the response was partial or none.
Miscellaneous Skin Problems
• Cushing's disease
Although this is not really a skin disease, the most notable symptom of this endocrine disease is the growth of heavy, coarse, often curly hair, which does not shed in the summer. This may be accompanied by sweating and seborrhea. This irregularly long and sometimes wavy hair often persists throughout summer months. Equine Cushing's disease is caused by a tumor in the pituitary gland, which is responsible for the production and regulation of hormones.
Curly hair in Cushing's disease (left) and Saddle pressure (right photo)
• Saddle eczema
An improperly fitting saddle may create pressure points on the horse's back muscle and cause the horse pain. Secondary bacterial infection may cause a folliculitis. So it is important that the saddle is comfortable for both the rider and the horse and eliminate saddle pressure from your horse's back. A horse can tell you in many ways if a saddle fits incorrectly. Objection to being saddled, resistance to work and training aids, front leg lameness, stumbling and tripping, not traveling straight, tail swishing and ear pinning, and hypersensitivity to being brushed all can be signs of a poor saddle fit.
• Vitiligo
Vitiligo refers to a skin depigmentation from an unknown cause, but is only a cosmetic problem. The skin is otherwise normal, but there is a gradual, often profound loss of pigment often around the muzzle, face, and eyes, and/or sometimes around the genitals. This pigmentation disorder has the same effect on horses as it does humans (like Michael jackson). Not much is known about Vitiligo (human or equine) such as the cause or how it is inherited. There is no known treatment.
Human and equine vitiligo
• Albinism
This is a genetic defect present at birth where melanin production is defective. These horses have white hair, white skin, pink eyes, and are sensitive to sunlight (photophobic). (> albinism)
• Pemphigus Foliaceus
This is a relatively common autoimmune skin disease that can become very severe and affect much of the body and causes destruction of normal skin cells. In a general sense, an autoimmune disease is one where the immune system of the animal recognizes normal cells and tissue as foreign. In the case of pemphigus foliaceus, the horse’s immune system attacks normal skin tissue causing changes to skin cells. It usually affects horses age 5 years and older.The destruction of skin cells occurs first on the face, belly, or limbs and can progress to involve the entire body. Initially, the affected areas are inflamed and develop fluid filled vesicles. These vesicles eventually rupture, leaving a break in the skin that begins to scale and crust. This problem can be diagnosed by taking a biopsy of an affected area and having that sample examined by a pathologist. These horses require high doses of steroids to suppress the immune system. Some animals require treatment with products like aurothioglucose, while others may require lifelong therapy.
• Alopecia
Alopecia is loss of hair. It comes in a variety of patterns with a variety of causes although often it is idiopathic. Possible causes are periods of high fever after serious illnesses, metabolic or hormonal causes, toxines from different plants (selenium), etc.
In most cases the hair coat will reappear within a few months. Treatment: biotin orally may be beneficial...
In the spring, horses can experience a seasonal alopecia in which large patches of hair shed out before entry of the new hair growth, leaving a bald patch of skin. The area of naked skin appears normal and the hair will reappear within about a month.
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The following is a list of questions a horse owner might be asked by a veterinarian when dermatologic (skin) problems occur:
• How long has the problem been going on?
• Do the symptoms come and go?
• If there is more than one lesion, where did you notice the first one?
• Do other horses, animals, or humans in close proximity have similar problems?
• Have there been any changes in the horse’s environment, diet, or supplements?
• Have there been any medications or vaccines given recently (orally, topically, or by injection)?
• Does the problem seem to be associated with certain seasons or types of weather (sun, rain, wet/humid)?
• Does the problem seem to be associated with any external parasites such as flies or biting insects?
• When was the last time you de-wormed your horse, and what product did you use?
• Have you noticed a change in hair coat?
• Does the problem seem to cause itching (pruritus)?
• Do the lesions seem to be associated with certain color patterns on the horse?
Frequently a diagnosis can be made from an accurate history and careful physical exam. Occasionally tests may be need to be run to identify the cause of the disease. There are many tools available to a veterinarian to help with a diagnosis. With so many skin problems in horses, the best form of diagnosis for any of the many would be to have your veterinarian biopsy the skin. The test is simple and gives minimal discomfort to the animal.
Taking a skin biopsy (a full thickness sample of the skin)
You will find most skin diseases and photos in: "Practitioners guide to equine dermatology" by Marianne M. Sloet van Oldruitenborgh-Oosterbaan and Derek C. Knottenbelt.
