The name ringworm is misleading since the disease is cause by a fungus, not a worm. Ringworm is a skin disease that affects cats and can be passed on to other animals, including humans.
Common name: Ringworm
Scientific name: Dermatophytosis
All cats are susceptible to developing the disease. However, young and old cats and cats that have a weakened immune system due to stress, medications or illness are more at risk. Cats living in crowded environments like shelters and catteries may also be at increased risk due to increased numbers of infective spores.
Ringworm is the most common infectious and contagious disease affecting the skin of cats.
Infection by ringworm is most common in warm geographic locations found in tropical and subtropical climates and during warm weather in temperate climates. It is more prevalent in communities that have large numbers of free-ranging cats.
Clinical signs (primary, most to least frequent, scientific term, synonyms)
Irregular or circular areas of hair loss. Some of the areas may have accumulated scales or crusts of dried skin cells. Miliary dermatitis (small pink or red firm bumps in the skin caused by inflammation).
Clinical signs (secondary, most to least frequent, scientific term, synonyms)
In some cases, the affected areas of the skin are itchy. Ringworm can also cause the cat's nails to become dry and deformed.
Causes (scientific, common term)
Microsporum canis, Microsporum gypseum, Trichophyton mentagrophytes.
Organ systems affected (most to least affected)
Hair coat, Skin, Nails.
Fungal culture, the most reliable method to make a definite diagnosis, Direct examination of hair and skin scales under the microscope, Examination with a Wood's light (false fluorescence common), Skin biopsy.
Allergic dermatitis, External parasites such as fleas, Skin infection.
The name ringworm is misleading since the disease is caused by a fungus, not a worm. Most cases of ringworm in cats are caused by the fungus Microsporum canis. Ringworm is a significant concern because it can be spread to other animals, including humans.
The disease develops when the skin surface comes in contact with fungal spores and the spores infect the hair shaft and follicle. Infected cats can have single or multiple areas of hair loss, which may have places of crusty or scaly dried skin and redness. Kittens are often affected on their faces, ears or front legs. The cats may or may not be itchy.
In some cases, the immune system of the animal is able to fight off the infection and no signs develop or they resolve quickly. Some cats are infected but show no outward effects, so they can still pass the disease on to others. Ringworm can be spread directly between animals in close contact with each other and can be spread indirectly through shared contact with brushes, bedding or other surfaces. This makes ringworm particularly problematic in shelters and catteries.
Since the fungal spores can be found on hairs and skin scales, the cat's environment must be thoroughly cleaned and disinfected. This can be accomplished through vacuuming carpets, floors and furniture. The cat's bedding should be washed with bleach. Surfaces should be washed with a detergent solution. Brushes used on the cat should be discarded or washed in diluted bleach water (1 part bleach to 10 parts water). Repeat all of the above for three cycles.
Humans handling affected cats should wash their hands frequently. Affected cats should be separated from other pets in the household.
A positive fungal culture is the most reliable method to determine if a cat has ringworm, but a veterinarian may also examine the cat's hair and skin scales under a microscope, look at the cat under a Wood's light or perform a skin biopsy to aid in the diagnosis. In some cases, infected areas will glow a bright apple-green under the Wood's light.
Once the diagnosis is made, the veterinarian will develop a treatment plan, tailored to the specific patient, which can include clipping the affected areas of the cat or the entire body, antiseptic baths and rinses, application of medicated creams, and treatment with oral antifungal medications. Patients with only minor clinical signs often do not require use of oral medications.
Diagnosis and a development of the treatment plan should be made by a veterinarian. Oral medications including itraconazole and terbinafine are often used and require close supervision by a veterinarian. Griseofulvin, an older medication, is no longer commonly used due to the potential for serious side effects.
Treatment should continue 1 to 2 weeks beyond resolution of the signs and a negative fungal culture to help prevent recurrence of the disease. The cat's environment must be cleaned to help prevent re-infection.
With appropriate treatment, cats are likely to have a full resolution of their signs.
Foil, C.S. Superficial Mycoses. In: Morgan, R.V., ed. Handbook of Small Animal Practice, 3rd Ed. Philadelphia: W.B. Saunders Company, 1997; 894-896.
Medleau, L. Dermatophytosis (Ringworm). In: Melman, S.A., ed. Skin Diseases of Dogs and Cats: A Guide for Pet Owners and Professionals. Potomac: DermaPet, Inc., 1994; 78-83.
Moriello, K.A., and Newbury, S. Recommendations for the Management and Treatment of Dermatophytosis in Animal Shelters. Vet Clin Small Anim, 2006; 36: 89-114.
Camille DeClementi, VMD
Steven Hansen, DVM, MS, MBA
© 2007. The American Society for the Prevention of Cruelty to Animals (ASPCA)