Despite its name, ringworm has nothing to do with worms at all. Called dermatophytosis by veterinarians, ringworm is actually a highly contagious fungal infection that affects the superficial layer of dead skin. Understanding how to tell if your cat has ringworm can help you treat the condition early and keep family members and other pets infection-free.
Ringworm pathogens belong to a group of fungi called dermatophytes, and the Microsporum canis dermatophyte is the species responsible for nearly every infection in cats as well as dogs and people. Ringworm fungi can be transmitted with direct contact with affected hairs. It can also spread through infectious spores clinging to grooming supplies, bedding, pet bowls and toys. Ringworm has an incubation period of 10 to 14 days before symptoms appear.
Because the ringworm fungi live in a cat's hair follicles, the hair shafts become fragile and easily break off near the skin line. The most common symptom of feline ringworm is small circular patches of hair loss, frequently accompanied by scaling skin. The bald, flaky skin occasionally has a red center. As the infection progresses, the patches of hair loss might enlarge and look less circular. Large patches of bare skin may crust over and ooze fluid. However, many ringworm infections are mild, consisting of only small, localized areas of red, flaky skin that look similar to dandruff. Ringworm typically doesn't cause itchy skin, so you might not see your cat scratching the infected spots. Cats most commonly develop ringworm infections on their faces, ear tips, tails, forelimbs and paws.
Vets often diagnose a case of ringworm through a visual inspection. However, since ringworm sores look similar to feline acne, staph infections and mange, many vets prefer to run additional tests on a cat's fur. Some vets examine potentially infected hairs using a Woods lamp, a special ultraviolet light set to a specific wavelength that causes the ringworm fungus to glow. The lamp definitively shows the infection in about half the cases.
Your vet might also choose to run a fungal culture, which is the most accurate test for diagnosing ringworm in cats. Vets pluck a few hairs from a skin lesion and place them on a special fungal isolation gel that changes color if ringworm fungi grow. Although accurate, fungal cultures take time to grow. Most kitties suffering from ringworm infections have positive cultures within 10 days, but it can occasionally take up to 21 days for an accurate diagnosis. Most vets start treatment before receiving the culture results if a cat shows typical ringworm symptoms, such as hair loss and lesions. If your vet wants to wait for the results, quarantine your cat in a small, uncarpeted room that is easy to clean, such as a bathroom or laundry room. Follow your vet's treatment and cleaning instructions exactly to keep the ringworm fungus from spreading.
A Few Considerations
Ringworm is a zoonotic condition, which means that the fungal infection can readily spread to humans and other animals. As soon as you suspect your kitty has ringworm, quarantine your pet in a small room without any carpeting until you can get her to the vet. Immediately after handling your cat, wash your hands thoroughly with soap and water and change and wash your clothes. Generally, if a family member doesn't have a ringworm infection by the time a vet diagnoses it in your cat, your family members aren't likely to catch it. Contact your physician if someone in your household develops skin lesions. Cases of ringworm in people typically respond quite well to treatment with over-the-counter products such as antifungal creams. Even with treatment, your infected kitty can stay contagious for approximately three weeks. Keep your kitty quarantined and minimize the exposure of family members and other pets to the affected cat during that time frame.