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Veterinary Health Center

Skin Conditions Continue After Summer

Mary Bagladi-Swanson, DVM, DACVD

As summer comes to an end, seasonal equine dermatology conditions may also be winding down. Itching or hives that were initiated by spring and summer pollens may wane or completely resolve. Horses that may have been rubbing their manes, tails or bellies, from allergic reactions to Culicoides gnats ("no-see-ums"), show signs of decreasing itch, as the insect populations die off.

Many dermatologic conditions, however, are not strictly seasonal. Although bacterial skin infections may be more prevalent in the summer, when the heat and humidity are high, the infections can occur year round. Staphylococcal folliculitis (bacterial infection and inflammation of the hair follicles) usually affects areas that are in contact with tack or blankets. These areas are more prone to skin abrasions, trauma, heat and moisture. You may notice papules (small bumps on the skin) that may be haired initially. Eventually, the hair falls out and the papules become scaly and crusty. Horses are not usually itchy, but may show signs of discomfort, associated with the affected skin. If predisposing factors, such as ill-fitting tack or poor grooming, are not corrected the condition can become chronic or recurrent. Eliminating predisposing factors, along with the use of mild antibacterial shampoos, often results in resolution of the lesions. Dermatophilosis ("rain scald") is another bacterial skin disease that frequently occurs in horses. Skin damage from coarse vegetation, abrasions, insect bites, etc., along with moisture, are required for the infection to become established in the skin. Areas frequently affected include the back, muzzle and pasterns. White haired, light skinned areas may be more severely affected. Horses develop thick scabs/crusts with tufts of hair protruding from the crusty lesions. Early skin lesions may have pus beneath each crust and are often painful. The condition can be treated by careful removal and proper disposal of the crusts, topical antibacterial treatment and keeping the horse dry. If the disease is severe, oral antibiotic therapy may also be necessary. Dermatophilosis is potentially contagious to other horses and is rarely contagious to humans.

Fungal infections are common in the fall, as well as other times of the year. Horses can develop dermatophytosis ("ringworm") after direct contact with infected horses. Also, horses may develop the fungal infection by contact with infected hairs or dandruff present on brushes, clippers, blankets and tack. The lesions are often found on the head, neck and sides. Horses infected with dermatophytosis have patchy, circular areas of hair loss and dandruff/scale. They may develop papules and the condition may resemble bacterial skin infection. The level of itch can vary, but is usually minimal. Microscopic examination of hairs might show evidence of fungal organisms, but a fungal culture is a more reliable diagnostic test. Most healthy horses can self-cure within a few months. However, topical antifungal therapy (antifungal rinses/dips) and environmental decontamination are utilized to hasten recovery and decrease potential contagiousness to other horses. Transmission from horses to humans is possible, but uncommon.

Pastern dermatitis ("scratches", "grease heel") does not have one, specific cause, but represents a reaction pattern that is unique to the horse. There are many different causes of pastern dermatitis, including bacteria, fungi, parasites, contact irritants and abrasions. As we enter fall and winter, some horses may be subjected to wet, soggy ground that doesn't readily dry out. Long fetlock hairs trap moisture and may favor the growth of bacteria or fungi. Both hind limbs are usually affected. The skin on the back of the pasterns may become reddened, scaly, crusty and thickened. Severely affected horses may be lame. If conditions are wet, the horse should be moved to a drier environment. Therapy may include clipping long fetlock hairs and gentle cleansing of the affected pasterns. Antibiotics may be needed, for cases that have bacterial involvement. Long-standing cases of pastern dermatitis are often poorly responsive to therapy.

It's advisable to routinely check over your horse's hair coat and skin in order to detect early signs of dermatologic disease. By thorough examination and diagnostic sampling, your veterinarian can recommend the best treatment plan for your horse.