Ringworm (Dermatophytosis)

What is Ringworm?

Ringworm (dermatophytosis) is a fungal infection of the hair, skin, and occasionally nails. Three species of ringworm cause the majority of infections: Microsporum canis (M. canis), Microsporum gypseum, and Trichophyton mentagrophytes. The most common sources of infection are other infected pets, rodents, contaminated environments, and soil. It occurs more frequently in kittens, puppies, immunocompromised animals, and long-haired cats. 

People who come in contact with infected animals are at risk of developing ringworm. As with animals, many individuals who are exposed will not develop an infection. Please consult your physician concerning this matter. You should also wash your hands well after handling your pet and use good hygiene.


The clinical signs of infection are highly variable. Skin involvement may be localized, multifocal, or generalized. Alopecia  (hair loss) is common because the infection infects the hair follicle and hairs are easily epilated. Classic circular patches of hairloss may be noted but it is important to consider other causes of hairloss such as bacterial skin infection and skin mites.  Bacterial skin infections are more common than ringworm in dogs and fungal culture is necessary to confirm infection.  Other signs may include red bumps, itching, crusting, scaling, and nail disease. When the nails are affected they may be broken and brittle, which may result in either loss of nails or nail deformities. However, ringworm nail infections are uncommon and a veterinary dermatologist should be consulted to evaluate for other diseases if nails are lost or deformed.

Diagnosis & Treatment

Ringworm diagnosis is based on Wood’s light examination (a special test with a certain type of light), fungal cultures, and/or skin biopsy. A Wood’s light  exanimation is only a screening test and ringworm culture is the gold standard for diagnosis. These cultures may take up to two weeks to grow and false negatives and false positives can occur if they are performed in-house.

Therapy for ringworm includes environmental clean up, topical therapy and in most cases oral antifungal therapy. Termination of treatment is based on physical exam and having two to three negative fungal cultures 2 – 3 weeks apar

Environmental Control

Isolate or confine affected pets to one part of the house (ideally in an easily cleaned, uncarpeted room). Vacuum daily and change the vacuum bag after each use. If possible throw away grooming aids, cat trees, collars and other infected items. Otherwise pet beds and blankets should be washed daily in water and bleach (1 cup/laundry tub with high water level and hot water). Use a Clorox solution (1:20 dilution) to disinfect all hard surfaces.

Treatment of Pets

Focal lesions may be treated with topical therapy alone. Antifungal creams, shampoos and dips may be utilized. Options include topical terbinafine, clotrimazole, enilconazole, ketoconazole, miconazole and lym sulur dips. For cats with ringworm and dogs that are unresponsive to topical therapy alone, oral systemic  antifungal therapy is indicated. Options include: terbinafine, itraconazole, and fluconazole.


The prognosis is good, except for endemic multicat households and catteries. Animals with immunosuppressive diseases also have a poorer prognosis for cure.