What is ringworm? Ringworm is a fungal infection of the superficial layers of the skin, hairs and nails. The fungi responsible for ringworm belong to a specialised group known as dermatophytes, and these can cause disease in both man and animals. Some species of dermatophytes will only infect man, or only infect certain animals, whereas others can be spread from animals to man. In cats, one type (species) of dermatophyte called Microsporum canis is responsible for almost all ringworm infections, and this species in addition to being infectious to both cats and dogs, will also readily infect man. What does ringworm look like? The most common clinical sign associated with ringworm infection is one or more areas of alopecia (hair loss) which occurs due to the increased fragility of infected hairs. Most typically, infection will produce a discrete irregular or circular patch of hair loss, accompanied by variable scaling, crusting, thickening and reddening of the skin. However, infection may sometimes cause other signs including generalised disease where a much larger area of the body is affected often with patchy hair loss. How can you diagnose ringworm infection? Diagnosis of ringworm infection is usually straightforward, although the disease has to be distinguished from a variety of other possible causes of hair loss. When hairs infected by Microsporum canis are examined under ultra-violet light (a Wood’s lamp), they often emit an apple-green fluorescence, and this is a simple and rapid test for the presence of this particular dermatophyte. However, not all dermatophytes cause fluorescence of infected hairs, and contamination of the hairs with other substances can also sometimes result in non-specific fluorescence. Confirmation of the diagnosis is therefore important and is made by microscopic examination of infected hairs and/or culture (isolation) of the fungus from hair samples submitted to a laboratory. Results from the latter test may take up to three weeks. Trea