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Scratches, Ringworm and Moose Ticks-Western Canada’s most common (and not so common) skin conditions.

posted by Horse Owner Today    |   March 2, 2011 21:30
Western Canada’s most common (and not so common) skin conditions.

         Dr. Sue Ashburner still shudders when she describes the sight of one of her equine patients covered with thousands of bloodsucking ticks last winter. “We occasionally see wood ticks on horses during May and June, but I didn’t know what kind of ticks would be on horses in February,” admits Ashburner, a veterinary clinician at WCVM’s Large Animal Clinic in Saskatoon, Sask.
               Dr. Lydden Polley, a parasitologist at the College, soon solved the mystery: he identified the parasites as Dermacentor albipictus (Acari: Ixodidae), more commonly known as moose ticks.
                “It was the first time I ever saw a horse in this area covered in moose ticks,” says Ashburner. “That’s what I like about working on dermatology cases. There are always new things, and those cases challenge you to find out what you’re dealing with. Sometimes we never know the cause, but we usually know how to treat what we see.”
               At least once a week, Ashburner gets a chance to use her dermatological know-how on equine patients living around Saskatoon — an area that’s populated with horses of all breeds and disciplines. The clinic’s number of dermatology cases usually rises in the spring after horses shed their coats and owners suddenly notice lumps, bumps, growths or parasites that have shown up during the winter.
               Thanks to advances in diagnosing and treating equine skin conditions, veterinarians can offer clients more effective therapies and more understanding of what causes skin problems to develop. Most clients call for advice or to arrange for a veterinary visit, but some still insist on using their own home remedies that often makes Ashburner’s job tougher. “After they’ve scraped it, treated it or used ointments that burn the skin, it doesn’t look anything like it originally did. These remedies usually just make things worse.”
               While Ashburner isn’t expecting another moose tick infestation case soon, here are some common skin conditions that she and veterinary pathologist Dr. Ted Clark regularly see out in the field and in the pathology laboratory. Their comments accompany some additional information gleaned from the text, Equine Dermatology, co-authored by Drs. Danny Scott and William Miller Jr. 
              
• Dermatophytosis or ringworm is a fungal infection that’s transmitted by contact with infected hair, bedding, tack and grooming equipment. Ashburner often diagnoses multiple cases of ringworm in young horses living in close quarters throughout the winter months: the infection often goes unnoticed until horses shed their winter coats.
               The most consistent clinical sign is one or many circular patches of alopecia (hair loss) with variable scaling and crusting. But horses may also develop the classic ring lesion with a healed centre and fine follicular papules and crusts on the ring’s edges. Lesions are usually multiple, and they’re most commonly found on the face, neck, the sides and girth. The lesions usually go away within three months, but veterinarians often use topical and systemic treatments to help their patients’ response to the infection, to reduce the spread of the fungus and to speed up the healing process.
 
• Sarcoids are the most common skin tumour of horses around the world. Veterinary researchers believe the cause of sarcoids is viral, and research has shown that bovine papillomaviruses (BVP) are commonly involved in sarcoid development. Lesions frequently show up in areas of a horse’s body after a wound or trauma, or they may also spread to other areas of the same horse or to other horses through biting, rubbing, tack, equipment and insects. Sarcoids occur anywhere on a horse’s body, but most lesions are found on the head, neck and ventral body surface. The lesions’ appearance can be verrucous (wart-like), fibroblastic (proud flesh-like), mixed verrucous and fibroblastic, and occult (flat).
               Sarcoids do not metastasize, and some tumours may disappear after several years. Depending on available resources, veterinarians can choose from surgical excision, cryosurgery, radio-frequency hyperthermia, laser therapy, radiotherapy, chemotherapy, immunotherapy or combinations of treatments. 
 
• Papillomas present in two different forms: as warts (viral papillomatosis) or as aural plaque (ear papillomas). Viral papillomas spread through direct contact or indirectly through contact with contaminated equipment or housing. Young horses often develop clusters of warts, usually on their muzzles or lips. “They bother the owner much more than horses,” says Ashburner. “If left alone, they tend to go away and you can’t rush them. People always buys potions and lotions, but they usually make no difference.”
               Aural plaques — white-greyish crusts commonly found in horses’ inner ears — don’t respond very well to topical treatments, and they rarely go away. Fortunately, these lesions are only a cosmetic problem.
 
• Eosinophilic granuloma or nodular necrobiosis is an equine dermatosis most commonly seen in the spring and summer. These nodules are round, elevated, and occur as single or multiple lesions on the back, withers and neck. The lesions aren’t painful or itchy, and the overlying skin and hair coat are normal. Veterinarians can surgically remove one or several lesions, or treat multiple lesions with systemic glucocorticoids over several weeks. Some lesions undergo spontaneous remission in three to six months, while older or larger lesions must be surgically removed.
 
• Allergic reactions show up as anything from bumps and wheals in all shapes and patterns to angioedema (swelling) involving the muzzle, eyelids, under the belly, legs or the entire body. These reactions result from insect bites, plants, drugs or vaccines, a change in feed, bedding or the horse’s environment.
               Gathering a thorough medical history is how veterinarians usually track down the source, says Ashburner. “It could be caused by a minor environmental change, a sudden hatch of bugs in the area. It really pays off to ask a lot of questions.”
               Ashburner and her colleagues usually try to eliminate the source of hypersensitivity or generally treat the horse to try and decrease its immune response. “One treatment that has worked quite well is to feed the horse raw linseed oil: its Omega 3 fatty acids help to decrease the animal’s hypersensitive response in the skin. That seems to calm things down and it helps to make the other treatments work better.”
 
• Scratches or pastern dermatitis most commonly affects one or both hind limbs with varying levels of pain and itchiness. The condition initially shows up as erythema (dew poisoning), swelling and scaling on the pastern, then progresses to discharge, matting of hair and crusting.
               Veterinarians usually diagnose this problem when there’s abrasive mud in corrals, or when ice crystals are mixed in the snow and dirt. “We think the moisture content has something to do with it: something seems to set up the right environmental conditions to induce scratches, particularly in the spring,” says Ashburner, adding that the condition usually shows up on a white leg. 
               “It responds very well if treated early, but it’s often missed by the owners until the horse’s pastern is very sore or very swollen. And the longer they have it, the harder it is to treat.” Severe cases of scratches can also lead to a longstanding, immune-mediated infection called vasculitis that can take months to cure.
               If diagnosed early, the ideal treatment is to clean the area very well with mild soap (no abrasive cleaners) then remove as much of the scabby debris as possible. Clipping the hair can help to remove the scabs. “We keep the area dry and use a topical cream — a combination of antibiotic and steroid cream — to fight the mixed infection,” explains Ashburner.
               Clark adds that it’s important for veterinarians to be aware that scratches isn’t “one specific disease with one specific cause.” If certain horses or horse herds continue to be plagued by this type of dermatitis, practitioners need to look at the animals’ environment, their habits and what they’re used for to learn more about probable causes.
 
• Rain scald (dermatophilosis) is a bacterial skin infection that causes superficial, pustular and crusting dermatitis in horses. These lesions are most commonly found on horses’ rumps, saddle area, face and neck — or on pasterns, coronets and heels (in the form of scratches).
               The two most important factors that lead to rain scald are skin damage and moisture. The condition is often diagnosed in horses after intense rain, and when temperatures and humidity are high. Veterinarians on the Prairies don’t often see rain rot, but it’s a common problem in B.C. 
               While most cases of rain rot go away within a month, the best treatments include keeping the animal dry, removing crusts, and using topical treatments and using systemic therapy if the infection is chronic or severe. 
 
• Melanomas are malignant skin tumours that are most commonly — but not exclusively — found in grey or white horses over six years of age. Arabians, Percherons and Lippizaners commonly develop these tumours that are often found on the undersurface of the tail and the perianal region. Tumours can also be found on the lips, base of the ear, on the legs, or anywhere else on the horse’s body. The melanomas are usually firm, nodular to plaque-like, and they may or may not be alopecic (hair loss), hyperpigmented or ulcerated.
               Veterinarians can use surgical excision or cryotherapy to remove solitary tumours, but in most cases, the tumours require no treatment.
 
• Insect hypersensitivity: Western Canadian horse owners and veterinarians deal with fewer parasitic problems than in other parts of the world because of the region’s cooler climate, but insect hypersensitivity is still a common problem in the spring and summer months. Controlling insects and using anti-itching agents can help to manage insect hypersensitivity. The use of ivermectin, moxidectin and other dewormers has also helped to reduce the occurrence of conditions like sweet itch, says Ashburner.
               - Sweet itch or Summer Seasonal Recurrent Dermatitis (SSRD): The most important cause of equine insect hypersensitivity is Culicoides gnats (sandflies, no-see-ums, biting midges). Affected horses develop itchy, crusted papules on the top of their tails, along their mane, neck, withers, hips, ears and forehead. The disease’s itchy nature causes horses to scratch and chew at themselves, or they may rub against stalls or fences. That can lead to hair loss, ulcer development and damage to the animals’ manes and tails.
               - Mange is caused by mite infestations in horses’ coats. Owners and veterinarians usually see these infestations during the late winter and early spring, and contributing factors include crowding, prolonged stabling, and poor nutrition.
               - Lice infestations are commonly found in horses during the winter when the animals’ coats are longer and they may be in close contact with their herd mates. Biting lice are usually found on the horses’ dorsolateral trunk, while sucking lice prefer the animals’ mane, tail and fetlocks. Clinical signs include scaling, a dishevelled coat, hair loss and mild to moderate itchiness.
 
 
 Reprinted with permission of Horse Health Lines, news publication for the Western College of Veterinary Medicine's Equine Health Research Fund. Sign up for the Horse Health Lines e-newsletter at www.ehrf.usask.ca