RiversideAnimalHospital Ringworm Information Sheet
(Dermatophytosis)
The term “ringworm” has been confusing to many people. Contrary to the common name of the disorder, there is no worm involved at all. The term ring worm actually refers to a type of fungus which lives on keratin, a major protein in skin, hair, and nails. The fungus usually lives on the hair shaft, but can colonize a layer of skin. Skin colonization tends to occur in kittens and Persians. The primary fungus involved with ring worm lesions is known as Microsporum canis. Microsporum gypseum is associated with lesions as well, however, this species lives primarily in the soil. Therefore, the soil is a source of ring worm for you and your pets. Trichophyton mentagrophytes is the third most common fungus of this type. Ringworm lesions are hairless, scaly, and can be associated with a poor hair coat around the lesion. The areas can also be red, darkly pigmented, and itchy.
Dermatophytosis, or “ringworm,” is transmitted by direct contact with an infective agent such as pet hair and dander from an infected cat, soil, or a rodent. Cats can carry the fungus without showing any signs of disease. This is more common in Persians and other long-haired cats. Ringworm can be transmitted to humans from their pets, the soil, and from other people. Humans transmit ringworm to each other far more often than we pick it up from our pets. Humans can transmit ring worm to their pets. The incubation period is generally considered one to four weeks. A healthy pet can contract the disease. Pets are at increased risk if they have another disease which compromises the immune system, are taking medications which suppress the immune system, are subject to poor nutrition, or live with a large number of other pets in a small area (such as in a cattery or kennel). (Two common underlying diseases in cats with ringworm are diabetes mellitus and infection with feline leukemia virus). In a healthy pet, dermatophytosis tends to go away by itself in two to six months. However, spontaneous recovery requires an intact functioning immune system.
Ringworm is diagnosed tentatively by exposing the lesion to a special light called a Wood’s light. The most common species of ringworm fluoresces a brilliant green in this light. Definitive diagnosis is based on culturing the organism.
Treatment for ringworm is recommended to shorten healing time and to decrease the chance of infecting other animals and humans. Topical treatment is administered in the form of creams, lotions, or shampoos. Most cats should be treated with oral medications. Treatment should continue for two weeks beyond negative culture results. The fastidious grooming that cats usually do is a protective mechanism. Long-haired cats are therefore more difficult to treat and cure. As a result, clipping long-haired cats is recommended to make treatment easier and to decrease the likelihood of infecting others.
While the pet is being treated, the environment should be also. Where possible use a 1:10 dilution of household bleach. Launder bedding and clothing with bleach and thoroughly vacuum.