The Classic Comprehensive Handbook of Cat Care
What to Do When Your Cat Is Sick: RINGWORM (DERMATOPHYTOSIS, DERMATOMYCOSIS)
Ringworm is an infection of the hair, toenails, or skin caused by special types of fungi that may be transmitted to cats from other animals, people, or the soil. Cats under one year of age are more often affected than other animals, and infection is most severe in animals weakened by other infections, parasites, or stress. The “classic” sign of ringworm is a rapidly growing, circular area of hair loss, but ringworm can appear in many other ways—scaly patches, irregular hair loss, crusts, and discolored, deformed toenails. Areas of reddened or darkened skin or small scabby bumps usually considered more typical of allergic reactions may also indicate ringworm. A ringworm infection can be present with no evidence of skin disease at all!
A HUMAN HEALTH HAZARD
Certain kinds of ringworm can be transmitted from cats to humans.
Adult humans are relatively resistant to ringworm, however, and are unlikely to become infected if normal hygiene habits are followed. Children should avoid handling animals infected with ringworm because they are more likely to become infected and tend to be less hygiene conscious. Infected cats should also be isolated from other uninfected pets to avoid spead of infection. Veterinarians can diagnose certain cases of ringworm with the use of an ultraviolet light alone (the most common type of ringworm, Microsporum canis, may fluoresce green). In other cases microscopic examination of skin scrapings and/or a fungal culture may be necessary.
An inexperienced person may confuse ringworm with other skin conditions such as allergies or mite infestation, and when cats show any signs of skin disease ringworm must be considered. If you are in doubt, see your veterinarian.
Many uncomplicated cases of ringworm heal spontaneously in one to three months, so isolated infected areas may be cleared with simple home care. The affected area should be clipped free of hair and washed daily in a miconazole, povidone-iodine (e.g., Betadine) or chlorhexidine shampoo, followed by application of an antifungal cream or drops. Products containing 2% miconazole nitrate or 1% clotrimazole, which inhibit the growth of ringworm, can be purchased in a drugstore without a prescription. They have been shown to be more effective than over-the- counter products containing tolnaftate. A 0.05% solution of liquid chlorine bleach applied once a day can be effective on localized lesions if more sophisticated products are unavailable.
Ringworm cases that do not respond to this simple regime, that have secondary bacterial infections, or that involve the toenails or several body areas need to have more extensive topical treatment as well as a prolonged treatment with systemic antifungal drugs. Topical treatments include dips of 2.5% lime sulfur, captan (1:200 dilution of 45% technical captan), 0.2% enilconazole, or 0.05% chlorhexidine. Griseofulvin is a common systemic drug used for treatment of more serious ringworm cases; it is incorporated into new hair growth to prevent recurrence of the fungus. Other antifungal drugs (e.g., ketoconazole) are also available on prescription by a veterinarian once an appropriate diagnosis is made.
Vaccines against ringworm can help eliminate signs of infection, but are no substitute for thorough treatment of infected cats.
PREMISES MUST BE CLEANED TO PREVENT REPEAT INFECTIONS
If your cat is diagnosed as having ringworm, clean your house thoroughly and change any air filters in your heating-ventilation system. Carpets should be steam cleaned at temperatures greater than 110°F (43°C). Wash and disinfect or discard your cat’s bedding, toys, scratching post, collar, harness and/or leash, and grooming equipment.
Products containing iodophors, chlorhexidine, or 0.5% chlorine bleach (5.25% solution of liquid chlorine bleach, mixed one part to ten parts water) are effective disinfectants that can be mopped or sprayed onto surfaces or used to soak certain washable materials. Cleaning should be repeated weekly until the cat is fully cured. The ringworm fungus forms spores (something like bread mold does), and thorough cleaning helps remove them and thus prevents reinfection. Untreated ringworm spores may survive in dry environments as long as four years!