Merck Manual

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Ringworm (Dermatophytosis) in Dogs

By

Sandra R. Merchant

, DVM, DACVD, School of Veterinary Medicine, Louisiana State University

Last full review/revision Jun 2018 | Content last modified Jun 2018
Topic Resources

Ringworm is an infection of skin, hair, or claws caused by a type of fungus. In dogs, about 70% of ringworm cases are caused by the fungus Microsporum canis, 20% by Microsporum gypseum, and 10% by Trichophyton mentagrophytes. In young or debilitated animals and in Yorkshire Terriers, infection may be persistent and widespread. The infecting fungus is spread easily in the environment. People can easily be infected with these fungi.

Most cases of ringworm are spread by contact with infected animals or contaminated objects such as furniture or grooming tools. Broken hairs with associated spores are important sources for spread of the disease. Contact does not always result in infection. Whether infection is established depends on the fungal species and on host factors, including age, health, condition of exposed skin surfaces, grooming behavior, and nutrition. Infection leads to short-lived resistance to reinfection. Under most circumstances, dermatophytes grow only in the dead cells of skin and hair, and infection stops on reaching living cells or inflamed tissue. As inflammation and host immunity develop, further spread of infection stops, but this process may take several weeks.

Ringworm, shown here on the shoulder of a dog, is caused by a type of fungus.

Ringworm, shown here on the shoulder of a dog, is caused by a type of fungus.

Infected dogs develop bald, scaly patches with broken hairs. Dogs may also develop acne-like bumps on the skin. The most common sites affected by ringworm are the face, ear tips, tail, and feet. Ringworm is diagnosed by fungal culture, examination with an ultraviolet lamp, and direct microscopic examination of hair or skin scale. Fungal culture of hairs and scrapings from the affected areas is the most accurate method. Direct microscopic examination of hairs or skin scrapings may allow early diagnosis.

Ringworm infections in healthy adults may clear up without treatment, but treatment might speed recovery and decrease the spread of the fungus in the environment. Medicated shampoos and dips are usually used to treat the entire coat. Diluted bleach can be used to clean the pet's environment. Additional, oral medications are needed in longterm or severe cases and are often necessary for Yorkshire Terriers. Your veterinarian can provide you with information about any treatment that may be appropriate for your pet and advise you regarding precautions you should take to avoid ringworm infection in yourself and members of your family.

Also see professional content regarding ringworm in dogs.

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