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Fungal diseases not just skin deep


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Because the infection is almost always follicular in horses, the most consistent clinical sign is one or many circular patches of alopecia with variable scaling and crusting, says Danny Scott, DVM, Dipl. ACVD, and William Miller Jr., VMD, Dipl. ACVD, professors at the New York State College of Veterinary Medicine at Cornell University. Some horses may develop the "classical ring lesion with central healing and fine follicular papules and crusts at the periphery."

Fungal culture of affected hair and scale is the most effective way to diagnose ringworm infection, to identify the dermatophyte, says Catherine Kohn, VMD, Dipl. ACVIM, professor at The Ohio State University College of Veterinary Medicine. Normal horses and those with non-fungal skin disease may be positively cultured as well as dermatophyte-infected animals.

"Where a practitioner can get into difficulty is possibly treating for something that isn't there," Kohn cautions.

Ringworm can look like sarcoids, summer sores, seborrhea, pemphigus, etc., so it needs to be identified properly.

"The antifungals are not going to be of much help if one is not treating a fungal condition," she says, so getting a skin scraping and finding the organism is a good plan prior to a treatment regimen.


If there is an outbreak in young horses, then management must be assessed in addition to treatment. Sometimes just getting the horses out in the sunlight will speed recovery, as well as improving their plane of nutrition and deworming them. If a practitioner sees many cases within a group of young horses, isolation protocols should be instituted, and equipment should not be shared between infected and healthy horses.

"Without improving management, one is probably not going to have a beneficial outcome," Kohn says. "Considerable dollars may be spent trying to treat the disease, when improved management would help quite a bit."

If a large surface area of the horse is affected, it's harder to treat, but the main approach should be topical.

"There is a sea of antifungal agents out there, although there is little evidence as to the efficacy of any of them, so it is difficult to give advice on the choice of topical medication based on evidence," Kohn says.

The goal of the therapy is to maximize the horse's ability to respond to the dermatophyte infection, so that means correcting nutritional imbalances, concurrent diseases, and getting rid of things like systemic anti-inflammatory drugs, which might depress the horse's immune system to fight the infection.

With a few lesions, creams and lotions can be applied topically twice a day. Lime sulfur washed over the affected area is reasonably inexpensive and is easy to apply. A large spectrum of products also can be used topically, such as chlorhexidine, miconazole, niastatin cream, thiabendazole and dexamethasone.

A good thing about the rinses is that you can easily treat a larger surface area of the horse if needed, as opposed to using a more expensive cream or ointment. The animal should be bathed daily for the first week, then bathed two times a week to control the infection. The treatment with tamed iodine shampoos, chlorhexidine shampoos or 5-percent lime sulfur solutions are often effective. When bathing with shampoos, it's best to work the shampoo into the skin and allow it to soak for at least 15 minutes before rinsing, sources say.

In well-managed conditions, you're usually dealing with a few lesions on one or a few animals. The rinse can be used daily, for a week or so, and cut down on your treatment once or twice weekly until the animal is cured. That's the general approach, which may take weeks to resolve, but it's better to treat it and get it done before you put the horse in contact with other animals.


Source: DVM360 MAGAZINE,
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