Despite its name, ringworm in cats has nothing to do with worms. Feline ringworm (dermatophytosis) is a fungal infection caused most commonly by Microsporum canis. It is one of the few animal infections that is genuinely zoonotic — meaning it readily spreads from cats to humans — making prompt treatment important for the entire household.
Ringworm is highly contagious between cats and from cats to people, particularly children, the elderly, and anyone immunocompromised. Understanding how to identify and treat it is essential for multi-pet households and families.
What Causes Ringworm in Cats?
Three main fungal species cause ringworm in cats:
- Microsporum canis — responsible for about 98% of feline cases
- Microsporum gypseum — soil-dwelling fungus, less common
- Trichophyton mentagrophytes — associated with rodent exposure
Spores are shed into the environment from infected animals and can survive on surfaces, bedding, and furniture for 12–18 months. Kittens under 1 year, long-haired breeds (especially Persians), and immunocompromised cats are most vulnerable. Healthy adult cats often carry spores asymptomatically.
Recognising Ringworm in Cats
Ringworm lesions in cats differ from the classic circular ‘ring’ rash seen in humans. Common presentations include:
- Circular patches of hair loss — often on the face, ears, forelimbs, or tail
- Scaly, crusty skin with broken-off hairs at the lesion edges
- Inflamed or reddened skin at lesion sites
- Miliary dermatitis — tiny crusts scattered across the body in some cats
- Asymptomatic carriage — cats with no visible lesions can still spread infection
A Woods lamp (ultraviolet light) causes about 50% of M. canis infections to fluoresce green, but a negative result does not rule out infection. The gold standard for diagnosis is fungal culture of hair and scale samples.
Treatment Approaches for Feline Ringworm
Effective ringworm management requires treating the cat AND decontaminating the environment simultaneously. Treatment typically lasts 6–12 weeks:
- Topical antifungals: Miconazole/chlorhexidine shampoo or lime sulfur dip applied 2–3 times weekly kills surface fungus and reduces environmental contamination. Clipping long-haired cats reduces spore load significantly.
- Systemic antifungals: Itraconazole (first-line) or terbinafine given orally for 3–6 weeks. Griseofulvin is older and less commonly used now due to side effect profile.
- Pulse dosing protocol: Itraconazole given week-on, week-off has proven effective and reduces cost.
- Treatment endpoint: Culture-negative results on two consecutive samples taken 2–4 weeks apart confirm resolution.
Environmental Decontamination
Ringworm spores persist in the home for over a year. Without aggressive environmental cleaning, reinfection occurs repeatedly:
- Vacuum daily and immediately dispose of the vacuum bag or empty the canister outside
- Steam clean carpets and soft furnishings
- Wash all bedding, fabric toys, and washable items in hot water weekly
- Disinfect hard surfaces with dilute bleach (1:10) or an enilconazole solution
- Discard items that cannot be reliably disinfected
- Restrict the cat to easily cleanable rooms during treatment
Protecting Humans in the Household
Anyone handling an infected cat should wear gloves and wash hands thoroughly with soap and water afterwards. Children should have limited direct contact until the cat tests culture-negative. People with ringworm lesions should see a doctor for topical antifungal treatment (clotrimazole or terbinafine cream). Immunocompromised individuals should minimise contact with infected animals entirely.