Spring Skin Things

Spring is an exciting time of the year. The weather is warming up and we’re all more than ready to get our horses out on the trails or into the show arena. But spring showers bring more than flowers; insects are an unfortunate side effect of spring. Wet weather and insects can combine to create a skin-tastrophe for your horses. Arm yourself with the knowledge to identify common skin issues and their basic treatments.

Skin issues usually seen in the wet months

Dermatophytosis
Commonly known as “ringworm”, dermatophytosis is a fungal skin disease commonly seen in the wetter months of the year. Caused by several species of fungi that are easily transmitted between horses through direct contact or shared equipment, outbreaks are usually seen when many horses are brought together for breeding or training. Infected hairs and scale can remain infectious in the environment for months. Although extremely contagious among horses, dermatophytosis is rarely transmitted to humans.
Dermatophytosis can be diagnosed by its clinical appearance and history. About 50-60% of cases can be confirmed by examining plucked hair with a microscope. Dermatophytosis typically appears as one or more circular patches of hair loss with scaling or crusts, often found on the face, neck, back or girth area. These are typically not itchy. Young horses tend to be predisposed to dermatophyte infections, however all ages and breeds can be affected. In healthy horses, dermatophytosis are usually self-limiting and tend to resolve on their own in 3 months.  
Although no treatment is necessary in healthy horses, horses undergoing steroid treatment should discontinue the use of steroids to allow for proper healing. Horses with Cushing’s disease typically have higher steroid levels in their body and should have their Cushing’s disease well-controlled in order to allow for proper healing. While a horse is recovering from dermatophytosis, the grooming supplies, tack and blankets of the affected horse should not come into contact with other horses. Shampoos containing the antifungal ingredient miconazole can be beneficial.  

Dermatophilus
Dermatophilus is a pustular and crusting skin disease. The culprit behind dermatophilus is an actinomycete bacteria easily recognized under a microscope due to its unique “railroad track” appearance. It needs two things to set up shop: moisture and damaged skin. Although commonly known as “rain rot,” even sweat under blankets and tack can provide enough moisture to support bacterial growth. The damage to skin can be a minor cut or even inflammation.
Dermatophilus is easily diagnosed by skin scrapes and microscopic evaluation. Dermatophilus is classically recognized by “paintbrush lesions” caused by serum drying and clumping hairs together in a crust that may have pus underneath it. Lesions are most common on the topline and saddle area but can occur anywhere. When seen on pink-skinned muzzles, it can be referred to as “dew poisoning.” Horses with chronic infections or in the healing phase have more dry crusts and hair loss. Horses suffering from dermatophilus are often not itchy.
The number one method of treatment is to keep the affected areas dry. If kept dry, dermatophilus can clear up on its own in as little as 4 weeks. Removing the crusts and “paintbrush lesions” is helpful, however they should be disposed of properly since they can be infectious for almost 4 years in the environment. Shampoos and soaks containing chlorohexidine can be helpful and should be used for 3-5 days consecutively and then once weekly until the skin infection has resolved. If the pink skin of a muzzle is affected, sunscreen should be used along with a chlorohexidine shampoo. 

Skin issues due to insects

Insect Hypersensitivity
Insect hypersensitivity is the most common skin disease of the horse and goes by several names such as “sweet itch” or “summer itch.” Insect hypersensitivity is a response to proteins in the saliva of Culicoides species, commonly called gnats, biting midges, punkies or no-see-ums. These insects bite horses indiscriminately, but some breeds may be more likely to have an adverse reaction.

Diagnosis is based on clinical signs and history. Signs of insect hypersensitivity usually begin to show around 3-4 years old and worsen with age. Clinical signs include intense itchiness along with small bumps called papules, most commonly around the mane, base of tail and rump, although other areas can be involved as well. In chronic cases, hair loss becomes evident in a rat-tail and buzzed off mane and the skin can become thickened like elephant skin. Due to horses scratching and biting themselves, the affected areas can easily become infected with bacteria.
The number one technique for controlling insect hypersensitivity is multifaceted insect control. Culicoides species are most active during dawn and dusk and are poor fliers. Therefore, keeping horses inside with strong fans blowing in the barn at these times and letting horses outside to graze overnight can drastically reduce their insect exposure. Topical anti-itching therapies include cold hosing and hypoallergenic/moisturizing shampoos. Systemic anti-itch treatments include antihistamines, omega 3 & 6 fatty acids and glucocorticoids (steroids). Antihistamines and omega 3&6 fatty acids are often not enough to control the discomfort on their own, but by using them in conjunction with steroids, the lowest effective level steroid can be achieved. 

Habronemiasis
Commonly referred to as “summer sores,” habronemiasis is transmitted by flies carrying the eggs of nematodes. Flies deposit them on the horse in moist areas and sometimes open wounds. Although flies carrying the nematode eggs can land on all horses, habronemiasis is most often seen in 1-2 horses in a herd.
Habronemiasis is commonly seen on the legs, belly, prepuce, inside corner of the eye, the crease of the lips, and in wounds. It is characterized by bumps of the skin (papules) or a chronic, non-healing wound with exuberant granulation tissue. Habronemiasis develops rapidly and quickly becomes ulcerated, oozing a blood-tinged exudate. Small yellow granules may be seen throughout the lesion under close examination. Lesions vary in itchiness.
Habronemiais can occasionally be diagnosed by a deep skin scrape and microscopic evaluation, however a biopsy gives a much better chance of definitive diagnosis. A combination of local and systemic treatment is used against this skin disease. Two doses of ivermectin or moxidectin can be given 21 days apart to treat the nematode larvae while a topical steroid ointment will help reduce inflammation and itchiness. If a wound is involved, a bandage should be placed over the wound to prevent further deposition of larvae by flies while the area heals.

These four unpleasant but manageable skin diseases are among the most common skin problems you are likely to encounter. If your horse is exhibiting symptoms that do not match these, or if the recommended treatment doesn't appear to be working, call your veterinarian