Dermatophytosis / Ringworm

Microsporum canis: circular alopecia
Kerion - Dermatophytosis / Ringworm
Equine hair affected by dermatophyte

Ringworm is an important cause of skin infection in cats and dogs. They are caused by fungi of the genera Microsporum and Trychophyton; Microsporum canis being the most frequently isolated fungus.

These mycoses are of great concern because they can contaminate humans (zoonoses).

Clinical signs

Ringworm manifests itself in different ways in dogs, cats and guinea pigs, but also from one individual to another. The clinical signs are :

  • a circular alopecia of slow centrifugal evolution with scales and crusts
  • an erythematosquamous dermatitis (redness and dandruff), sometimes pruritic
  • a generalised kerato-seborrhoeic state which is expressed by an oily skin and coat
  • generalised squamous dermatitis (dandruff all over the body)
  • milliary dermatitis (multiple small scabs) in cats
  • nail bed (perionyxis) or nail bed (onyxis) involvement
  • a localised inflamed lesion (kerion)

The diagnosis

Clinical suspicion of ringworm must always be confirmed by a rigorous experimental diagnosis. This is mainly based on four additional examinations:

  • Wood's light examination which causes a violet fluorescence of the affected hairs
  • microscopic evidence of fungal invasion of the hairs
  • fungal culture
  • histopathological evidence of hair or stratum corneum invasion


Although dermatophytes can heal spontaneously in a few months in immunocompetent individuals, it is not at all desirable to recommend a wait-and-see attitude given the contagious nature of ringworm and the risk of zoonosis. The objectives of treatment are to accelerate recovery, to reduce or prevent the spread of spores in the environment and to limit contagion.

  • Shearing the coat is recommended (especially in Persian cats) as it removes the infected hair. However, it can worsen the situation during the first few days. Indeed, during this period spores are disseminated in the environment and cutaneous microtraumas are created favouring the dissemination of the fungus on the skin
  • Topical treatments should be used on the whole body in most cases. They help to limit environmental contamination
  • Systemic (oral) treatment, the most interesting molecules are griseofulvin, ketoconazole and itraconazole. In Belgium, only itraconazole (Itrafungol™) is registered to treat cats with ringworm
  • Treatment of the environment is essential because spores can survive up to 18 months in the environment and there can be 1000 spores/m³ of air in a house where an infested cat is staying. Treatment should be preceded by mechanical cleaning using a hoover, which will destroy the contaminated bag. Fabrics, blankets and cushions should ideally be destroyed. Disinfection of the premises must follow the mechanical cleaning and must be repeated throughout the treatment of ringworm
  • Vaccination has raised great hopes, but so far there is no scientific evidence to recommend its use

Ringworm should therefore never be considered as a minor disease. Its treatment must be rigorous because, in addition to curing your pet, it is important to avoid human contamination (zoonosis).

Wood lamp examination - Dermatophytosis / Ringworm
Human infection / Tinea corporis (Iowa University picture)