Ringworm (dermatophytosis) in cats is a fungal skin infection caused primarily by Microsporum canis. Despite the name, it has nothing to do with worms. It is highly contagious between animals and can spread to humans, making it both a welfare and a zoonotic public health concern.
Causation and Epidemiology
Microsporum canis accounts for approximately 95% of feline dermatophytosis. The fungus infects keratinised tissues — hair shafts, skin surface, and claws. Spores can persist in the environment for months to years. Kittens, immunocompromised cats, and Persian cats are particularly susceptible. Long-haired cats can carry infection asymptomatically, acting as reservoirs.
Clinical Signs
- Circular areas of hair loss (alopecia) with scale and crusting — classic "ringworm" appearance
- Broken hair shafts within lesions
- Varying degrees of pruritus — some cats are intensely itchy, others barely affected
- Lesions most common on face, ears, and forelimbs
- Asymptomatic carriers may show minimal or no visible lesions
Diagnosis
Wood's lamp examination reveals apple-green fluorescence in approximately 50% of M. canis infections — useful screening tool but not definitive. Microscopic examination of hair using 10% KOH or lactophenol cotton blue reveals fungal hyphae and arthrospores. Fungal culture on dermatophyte test medium (DTM) is definitive and essential for species identification — critical for zoonosis management.
Treatment
Topical treatment: Enilconazole rinse (twice weekly), miconazole/chlorhexidine shampoo, or lime sulphur dip are highly effective topical treatments. Regular application throughout the 6–12 week treatment course is essential.
Systemic antifungals: Itraconazole (pulse dosing: 1 week on, 1 week off) or terbinafine for widespread disease or where topical treatment is impractical.
Environmental decontamination: Dilute bleach (1:10), Virkon-S, or Accelerated Hydrogen Peroxide products kill dermatophyte spores on surfaces. Vacuuming to remove infected hair and thorough cleaning of all cat contact surfaces is essential to prevent reinfection.
Zoonotic Risk and Welfare Management
Humans, particularly children and immunocompromised individuals, can contract ringworm from infected cats. Lesions on human skin respond well to topical antifungal creams. During treatment, infected cats should ideally be isolated or their contact with humans minimised. Gloves should be worn when applying topical treatments. This zoonotic dimension makes prompt, effective treatment important for both cat and human welfare.