Ringworm (Dermatophytosis) in Cats

Dermatophytosis is a highly contagious and common infection that is easily transmitted to other animals and to humans. Cats with the symptoms of dermatophytosis require veterinary attention.All in-contact animals and humans require examination and treatment once a cat in the home has been diagnosed with ringworm.

Although dermatophytosis is not life-threatening, the fungal spores last for months in the environment. As such, disinfection of the home and quarantine of infected animals are required to resolve the infection. Infections often last longer than 6 weeks even with treatment and excellent hygiene.

Some cats can become carriers of the fungus while showing no symptoms. In these cases, cats are contagious to other animals and people without becoming infected themselves.

Cats with severe dermatophytosis have many patches all over the body. In cases where the fungus causes itchiness, scratching induces more damage to the skin, which encourages further infection.

Cats with dermatophytosis of the claws can have whitish or opaque nails that are rough in texture.

Cats who are particularly susceptible to dermatophytosis include those who:

• Spend time outside
• Are young
• Are immunocompromised (such as those who are FeLV or FIV positive)
• Live in warmer climates
• Have cancer, intestinal parasites, or poor nutrition
• Live in close contact with other animals
• Have roughened skin due to fleas, sores, wounds, or other skin trauma
• Live in close contact with other cats, including in kennels, breeding operations, feral cat colonies, shelters, or pet stores

Longhaired cats such as Persians and Himalayans are predisposed to this infection.

Dermatophytosis is caused by a number of different fungi. The most common pathogenic fungus for the skin, hair, and nails of cats is Microsporum spp.. The fungus releases spores which cling to hair and other surfaces. In cats with strong immune systems and where the skin is undamaged, the spores are usually unable to invade the skin surface, preventing infection. In cats who have weaker immune systems, or whose skin is damaged, the spores invade the skin layers and reproduce. The fungus thrives on skin and hair because they are composed of keratin, which the fungus uses as a nutrient source.

Diagnostic tools to confirm ringworm include:

• Physical examination
• Dermoscopy (an examination of the skin under magnification)
• Microscopic examination of hair and skin scales
• Fungal culture
• Specialized bloodwork to detect dermatophyte DNA
• Skin biopsy

A tool called a Wood’s lamp is sometimes used. This tool detects fluorescence under UV light, however most of the fungi that cause dermatophytosis do not fluoresce.

Treatment for dermatophytosis is antifungal medication. Treatment requires diligence and is ongoing until the infection is proven by laboratory tests to be resolved. The absence of symptoms does not mean that the infection is gone.

During the treatment period, affected animals must be isolated from all other pets and any humans interacting with the animal must wear protective equipment to prevent infection. Clipping long-haired animals is recommended to reduce contamination of the quarantine environment. Cats undergoing oral antifungal treatment require repeated bloodwork to monitor for side effects of these medications. Older cats may require additional work-up to identify any underlying conditions, as many cases of ringworm are associated with immunosuppression.

Treatment alone is not sufficient for recovery. Disinfection of the cat’s environment is necessary. The spores that are constantly being produced by the fungus last in the environment for a long time. All spores must be disinfected from the home before the recovered cat is reintroduced. Environmental decontamination requires extensive cleaning, since the spores are usually abundant and are invisible to the naked eye.

Strategies for ridding the environment of the spores include:

• Extensive daily vacuuming
• Carpet shampooing with a disinfecting detergent that is allowed to sit on the carpet for 10 minutes
• Laundering all bedding and other fabrics thoroughly
• Disinfecting and/or scrubbing hard surfaces with bleach solution or high-quality cleaners
• Discarding all items that cannot be washed or disinfected

Household disinfection is required on an ongoing basis until the contamination is proven to be over. Household decontamination alone is not sufficient to successfully cure ringworm. Veterinary prescribed medication in combination with environmental decontamination and quarantine protocols are the only way to fully resolve ringworm in pets.

Confirming decontamination requires laboratory testing of samples taken from the home environment.

Cats and their environment are often still contagious when the symptoms of dermatophytosis are gone, therefore confirmation of both the recovery of the cat and the decontamination of the environment by laboratory testing are required to avoid reinfection.

External parasite control for fleas and ticks is especially important in cats with dermatophytosis, since the scratching creates more skin damage which results in further infection.

Without treatment, dermatophytosis takes 9 months to a year to resolve, during which time the cat continues to be contagious.

Even with treatment and excellent hygiene, dermatophytosis takes longer than 6 weeks to resolve. In many cases, insufficient decontamination and quarantine measures result in repeated reinfection, prolonging the recovery period.

Prevention of dermatophytosis centers around maintaining excellent health of pets in the home. Cats who are kept inside and away from other animals are less likely to be infected. Providing good quality food, seeking regular veterinary care to diagnose underlying conditions early, and observing the cat closely for early symptoms of associated conditions are recommended.

Dermatophytosis is common. It is more common in locations with warm, humid climates.

• Antifungal medication
• Environmental decontamination
• Monitoring
• Quarantine