Feline Ringworm (Dermatophytosis): Wood's Lamp, Treatment, and Zoonosis Prevention

Feline ringworm (dermatophytosis) is a superficial fungal infection of the hair, skin, and claws primarily caused by Microsporum canis (responsible for over 95% of feline cases). Beyond creating patchy circular hair loss and crusts on a cat's ears and muzzle, ringworm is one of the most common and contagious feline zoonoses, easily transmitting to human family members—particularly children and immunocompromised individuals—to form itchy, red, circular 'bullseye' skin rashes.

Sources

This guide is not a substitute for a vet.Veterinary Emergency Clinic Directory

Veterinary clinical inspection of a cat showing focal alopecia from dermatophytosis ringworm — Foto: Nekolife

In this guide

1. Etiology and Zoonotic Transmission to Humans

Microsporum canis digests keratin within hair shafts, weakening the hair until it fractures flush with the skin. Direct physical contact with an infected cat or contaminated shedding hairs transfers spores to human skin.

In people, this results in tinea corporis, presenting as expanding red circular rings with raised borders and central clearing that itch intensely. Persian cats and young kittens with immature immune systems are overrepresented.

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2. In-Clinic Veterinary Diagnostics

Accurate diagnosis is paramount before starting long-term treatments:

Wood's Lamp Examination: Ultraviolet light reveals striking apple-green fluorescence along infected hair shafts in roughly 50-60% of cases.
Microscopic Trichogram: Examination of plucked hairs reveals fungal hyphae and arthroconidial cuffs disrupting normal hair structure.
Dermatophyte Test Medium (DTM): Fungal culture medium turns bright red simultaneously with the appearance of white fluffy colonies within 1 to 2 weeks.

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3. Medical Treatment Protocol: Systemic & Topical

Oral Antifungal: Itraconazole administered using an alternating pulse-week regimen (one week on, one week off) offers optimal efficacy and minimal liver stress.
Topical Therapy: Twice-weekly medicated dips with lime sulfur, enilconazole, or miconazole/chlorhexidine shampoos sterilize coat surface spores.
Cure Confirmation: Treatment must continue until two consecutive negative fungal cultures are achieved 14 days apart.

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4. Home Decontamination and Spore Elimination

Spore persistence in carpets and upholstery causes chronic relapses. Launder bedding in hot water (>60°C / 140°F), discard used vacuum cleaner bags promptly, and wipe non-porous surfaces with dilute sodium hypochlorite.

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Scientific Sources and References

Moriello, K. A., et al. (2017). Diagnosis and treatment of dermatophytosis in dogs and cats: WAVD Clinical Consensus Guidelines. Vet Dermatol, 28(3), 266-e68.
Frymus, T., et al. (2013). Dermatophytosis in cats: ABCD guidelines. JFMS, 15(7), 598-604.

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