It’s spring, and in veterinary clinics across the country kittens and the animals that have been in contact with them are being diagnosed with ringworm. Okay, it’s not fair to blame kittens for every case of ringworm, but that soft and fluffy feline coat may be harboring an uninvited guest.
Let’s get this out of the way first — ringworm (more correctly called dermatophytosis) has nothing to do with worms. It got the name because the raised ring that is a characteristic of the infection in people, but not pets, looks a bit like a worm lodged underneath the skin. Ringworm is a type of fungal infection that most commonly affects the skin, fur and nails of cats, particularly kittens, and less frequently dogs and other species. Cats don’t just get the disease more frequently than do other animals, they also shed LARGE numbers of fungal spores when they are infected. So while the ringworm fungus can be found virtually everywhere in our environments, contact with an infected kitten or cat is often responsible for overwhelming a person or pet’s natural defenses.
The most common signs of ringworm infection in cats and dogs are hair loss, itchiness, flaky skin, and brittle or misshapen nails. It is important to note that some cats can be asymptomatic carriers, meaning that while they look perfectly normal themselves, they can be a source of infection for other individuals in the household.
Unfortunately, the symptoms of ringworm fit with just about every dermatological condition we see as veterinarians. The most commonly used diagnostic test involves plucking hairs from affected parts of the body, pushing them into a special type of growth medium, and waiting up to three weeks to see what grows. Some veterinarians will use a black light to identify which parts of the body are potentially harboring ringworm organisms (some types fluoresce), but examination by black light alone cannot definitively diagnose or rule out ringworm. In difficult cases, a skin biopsy might be necessary to reach a definitive diagnosis. Something called a toothbrush test — essentially brushing a pet’s fur with a toothbrush and then poking the bristles into a fungal growth medium — is a good way to screen potential asymptomatic carriers.
If anything, treating ringworm is even more difficult than diagnosing it. Mild to moderate cases may respond to medicated baths, lotions or dips (e.g., lime-sulfur, miconazole, chlorexidine). Shaving pets with long fur can help the medications reach the skin and reduce the number of contagious fungal spores present. In severe cases, oral anti-fungal drugs, such as griseofulvin or itraconazole, are often necessary. For large dogs when cost is a concern, ketoconazole can also be considered. Oral flea preventatives containing lufenuron may also help eliminate ringworm but should not be used alone.
Treatment generally needs to continue for several months and should not be stopped until hair is starting to regrow and fungal cultures are rechecked and found to be negative.
Because ringworm is so contagious, animals undergoing treatment need to be isolated and owners should decontaminate the parts of the home where infected critters have spent time. Vacuum floors, rugs and upholstery thoroughly, and wash everything possible in hot water and dry on a hot setting. A one part bleach to thirty parts water solution will kill the fungus on hard surfaces that can handle such treatment.
As always, wash your hands thoroughly after handling any pet, especially if it might have ringworm.
Dr. Jennifer Coates