Ringworm (Dermatophytosis)

Ringworm is a misnomer — there is no worm involved. Dermatophytes are fungi that digest keratin, the protein found in skin, hair, and nails. They are uniquely adapted to colonise the superficial layers of the skin without invading deeper tissues in healthy hosts.

Microsporum canis accounts for approximately 98% of feline ringworm cases. Infection spreads via direct contact with infected animals or contaminated fomites — brushes, bedding, furniture, or surfaces where infected hairs have settled. The incubation period is 10–14 days. Infected hair shafts become brittle and break off, producing the characteristic circular alopecic lesions. Lesions are most common on the face, ears, and forelimbs.

Long-haired cats — particularly Persians — are significantly more susceptible, possibly because their dense coats create a warmer, more humid environment that favours fungal growth, and because grooming distributes spores across more body surface area.

Treatment duration is typically 6–12 weeks, and treatment must continue for at least 2 weeks beyond clinical resolution and two negative fungal cultures taken one week apart. Stopping too early causes recurrence. Oral itraconazole or terbinafine combined with twice-weekly antifungal shampoo (miconazole/chlorhexidine) is the most effective regimen.

Environmental decontamination is critical and often overlooked. Infective spores on shed hairs can survive for up to 18 months. Vacuum thoroughly, steam clean carpets, wash all bedding at 60°C, and disinfect hard surfaces with dilute bleach (1:10 household bleach) or an accelerated hydrogen peroxide product.