Ringworm is an infection of skin, hair, or claws caused by a type of fungus known as a dermatophyte. In cats, about 98% of ringworm cases are caused by the fungus Microsporum canis. The fungus is spread easily in the environment and often infects people (see Disorders Affecting Multiple Body Systems of Cats: Fungal Infections in Cats).
The fungi spread to people primarily by contact with infected cats and 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 habits, and nutrition. Infection leads to temporary 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.
Infected cats can develop circular, bald, scaly patches with broken hairs in ring-like whirls. The center of the rings can regrow darker than normal hair. The most common areas for ringworm to occur are the face, ear tips, tail, and feet.
Veterinarians diagnose ringworm 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 clear up without treatment, but cats with widespread ringworm are most often treated with anti-fungal medications prescribed by a veterinarian. Treatment with medicated shampoos can speed healing in some cases. Such treatments are not always effective, however. 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.
Last full review/revision July 2011 by Karen A. Moriello, DVM, DACVD; Thomas R. Klei, PhD; David Stiller, MS, PhD; Stephen D. White, DVM, DACVD; Michael W. Dryden, DVM, PhD; Carol S. Foil, DVM, MS, DACVD; Paul Gibbs, BVSc, PhD, FRCVS; John E. Lloyd, BS, PhD; Bernard Mignon, DVM, PhD, DEVPC; Wayne Rosenkrantz, DVM, DACVD; Patricia A. Talcott, MS, DVM, PhD, DABVT; Alice E. Villalobos, DVM, DPNAP; Patricia D. White, DVM, MS, DACVD