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Ringworm

Despite its name, Ringworm is caused by a fungus Microsporum canis, not a worm. The fungus invades the hair and hair follicles. Ringworm is also called Dermatomycosis or Dermatophytosis. It is a potentially contagious zoonotic disease. More than 30% of cats may be asymptomatic carriers of M. canis.

The typical appearance of ringworm lesions is a spreading circle with hair loss and scaly skin at the centre and an advancing red ring at the margin.

Ringworm in cats is not as obvious in appearance. There may be scaly patches, irregular hair loss or a few broken hairs around the face, ears or paws. There can be extensive skin involvement. Simple ringworm is not itchy but scabs and crusts can form leading to draining sores that provoke licking and scratching.

Ringworm usually occurs in young cats, poorly nourished cats and cats whose immune system is depressed by disease. It is most common in longhaired breeds.

The disease is transmitted by direct contact with infected animals or indirect contact from a contaminated environment - by contact with infective hair of dogs and cats found on carpets, brushes, combs, toys and furniture.

Cats carry the fungus without showing any apparent infection and may be a source of infection for other pets in the house.

Humans can pick up infection from cats and also transmit disease to them. Children should avoid handling cats with ringworm because they are more susceptible to infection than adults.

A diagnosis can be made if the affected area glows green (fluoresces) under ultraviolet light (Woods lamp), but only 50% of Microsporum canis cases will glow. Microscopic examination of skin scrapings or fungal cultures can also be used for diagnosis.

Treatment

The disease in animals is usually self-limiting. Mild cases regress spontaneously and recurrence is uncommon. Because the disease is highly contagious, animals are usually treated to prevent infection of other animals or people in the house.

Oral antifungals are often prescribed for ringworm. Griseofulvin is the drug of choice, but it should not be given to pregnant queens because it may cause birth defects.

For a localized infection, the infected hair is clipped away at the margin of the ringworm lesions and the skin cleansed with betadine solution. An antifungal cream may be applied to the affected area and the surrounding skin and hair once a day. Oral antifungals may be given instead, because cats tend to lick creams off.

Generalized ringworm requires extensive clipping of infected hair and oral antifungal treatment.

Prevention

Spores can survive for up to 1 year in the environment. They should be eliminated from the house to prevent reinfection. The cats bedding should be discarded. Sterilize all grooming equipment in a dilute solution (1:10) of bleach. Thoroughly clean the house and vacuum the carpets weekly to remove infected hair. Mop and wash hard surfaces (floors, benches, counter tops, cattery runs) with dilute bleach.

Strict hygiene is required to prevent human infection. Rubber gloves should be worn while handling and treating infected cats.

Boil contaminated clothing and fabrics or wash them in bleach to kill spores.

Ringworm is highly contagious and requires immediate veterinary attention to prevent further spread.

References

Carlson DG & Giffin JM, Cat Owners Home Veterinary Handbook, New York: Howell Book House, 1995

Tilley LP & Smith FWK, The Five Minute Veterinary Consult - Canine and Feline (2nd Edition), Philadelphia: Lippincott Williams and Wilkins, 2000

Wilks CR & Humble MW, Zoonoses In New Zealand, Massey University, 1997

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