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Dermatophytosis (Ringworm)

Dermatophytosis is a fungal skin infection of animals that affects the hair and surface of the skin. It is commonly known as ringworm since the lesions often appear ring (round) in shape!

The most common organisms associated with dermatophytosis are Microsporum canis, Trichophyton mentagrophytes and Microsporum gypsum.

All of these organisms (dermatophytes/fungi) are infectious to humans. Animals with a weakened immune system (due to age e.g. young animals, disease or drugs) are more at risk of developing a ringworm infection.

Clinical signs

Some animals can be infected as carriers showing no clinical symptoms. Hair loss is the most common sign, which may be present together with crusty scaling, dandruff, redness, increased pigmentation and itchiness.

Diagnostic tests

A definitive diagnosis can be made by a fungal culture. A culture will provide a medium for the fungus to grow, which normally takes 2 weeks. A culture normally involves either brushing the hair with a sterile toothbrush or plucking a small sample of hair form the edge of the lesion. It is important that no antiseptic/antifungal creams or shampoos have been used prior to taking a culture sample.

Wood’s lamp examination can also aid a ringworm diagnosis. Hairs that exhibit a positive apple-green fluorescence under a blue light is considered a positive result for Microsporum canis. It is worth noting that many false negative and positive results can occur with a Wood’s lamp exam.


If the infection is localized, it is common to use just topical therapy such as a cream or shampoo. If the infection is persistent or generalized (affecting many parts of the body), we commonly use antifungal medicine such as griseofulvin, itraconazole or ketoconazole, in addition to shampoos (which minimize environmental contamination). Treatment normally is continued for 1-2 months.

It is also important to isolate affected animals to reduce spreading the fungal infection. Cleaning infected surfaces/areas with bleach and detergents and using a vacuum cleaner to remove all hair that has been shed will help to prevent re-infection.

It is important to remember that humans can also be infected with ringworm, so good hygienic measures such as washing hands will help minimize you getting the disease yourself!