Feline Ringworm Infection

What is ringworm?

Despite the name, ringworm is not a worm. It is an infection of the skin, hair, and claws by a fungus, most often Microsporum canis. The name comes from the round, red, scaly lesions it produces on people. Cats are the most common carriers of this fungus, and kittens, long-haired cats, and cats living in crowded conditions such as shelters are affected most often.

How do cats get ringworm?

By contact with an infected animal or with fungal spores in the environment. Spores shed on hairs can survive in carpet, bedding, brushes, and furniture for well over a year. Some cats carry the fungus without any visible lesions and still spread it.

What are the signs?

• Circular or irregular patches of hair loss, most often on the head, ears, and front legs
• Scaly, crusty, or reddened skin, sometimes with broken hairs that look stubbly
• Dandruff-like flaking
• Occasionally, brittle or misshapen claws
• Itching is usually mild, unlike many other skin conditions

Many other skin problems look similar, so a diagnosis is needed before treatment.

Can people catch it?

Yes. Ringworm is zoonotic, and children, the elderly, and anyone with a weakened immune system are most susceptible. It appears as itchy, ring-shaped red patches on the skin. Wash your hands after handling an infected cat, keep the cat away from bedding and furniture where possible during treatment, and see your doctor about any suspicious spots on yourself. Human infections are treatable.

How is ringworm diagnosed?

A Wood's lamp (ultraviolet light) makes some strains of the fungus glow apple-green on the hair shafts, but not all strains fluoresce. Examining plucked hairs under the microscope, a fungal culture that takes one to three weeks to grow, or a PCR test that detects fungal DNA in a few days confirms the diagnosis. Culture or PCR is also how we confirm the infection is gone at the end of treatment.

How is it treated?

Ringworm can eventually clear on its own in a healthy cat, but treatment shortens the course from months to weeks and greatly reduces spread to people and other pets. Treatment combines:

• Oral antifungal medication, usually itraconazole or terbinafine, given for several weeks
• Topical treatment, most often lime sulfur dips or an antifungal shampoo twice a week, which kills spores on the coat and reduces contamination of the home
• Clipping long-haired cats to make topical treatment effective

Treatment continues until two consecutive cultures or PCR tests are negative, typically six to twelve weeks. Stopping when the lesions look better is the most common reason for relapse.

How do I clean the house?

Spores are the reason ringworm keeps coming back. Vacuum thoroughly and often, discarding the bag or emptying the canister outside. Wash bedding, blankets, and soft toys in hot water. Wipe hard surfaces with a disinfectant labeled for fungal spores or diluted bleach (one part bleach to ten parts water) where the surface allows it. Confine the cat to one easily cleaned room during treatment when you can, and keep other pets away until they have been checked.

See also: Canine Ringworm Infection