Ringworm is a skin infection caused by a variety of fungi known as the dermatophytes. The name Ringworm comes from the appearance of the typical red circular lesion seen in the skin of infected people.

Some of these fungi are zoonotic and can be transmitted from animals to humans. In immunocompetent ( normal immune status ) humans, the infection of these fungi is usually limited to the outer (keratinized) layers of the skin and hairs and results in the typical "ringworm" lesion.

In immunocompromised (a poor immune status) humans however, these fungi may cause systemic infections.

Ringworm lesions in animals may be less obvious than in humans and they may present in a variety of ways such as a diffuse folliculitis, an area of alopecia (hairloss) or even an ulcerated lesion.

However, it is important to realise that cats (and to a lesser extent dogs) can be asymptomatic carriers or vectors of the infection. In other words they can pass the infection onto humans without themselves showing any clinical signs.

The risk of infection is greatest from kittens and from cats/kittens that come from shelters or catteries with a history of this problem.

Another important issue with regard to ringworm is treatment. If a human needs treatment for ringworm then it is commonsense to try to establish the origin of the infection and treat that as well. Thus it is not uncommon to have both human and pet being treated for the same infection at the same time!