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Ringworm: A Persistent Fungus


Pet Column for the week of December 15, 2003

Related information:

Services - Dermatology
Services - Public Health

Office of Public Engagement
2001 S. Lincoln Ave.
Urbana, Illinois 61802
Phone: 217/333-2907
Ann Marie Falk
Information Specialist

"Ringworm is very badly named because it is caused by a fungus not a worm," says Dr. John Angus, a veterinary dermatologist at the University of Illinois Veterinary Teaching Hospital in Urbana. "Ringworm makes its home on the hair and skin, and it affects both people and pets. In humans, ringworm forms a ring-shaped, raised red rash, but this presentation is not common in animals. Ringworm can look like anything!"

Dogs and cats are susceptible to three forms of ringworm. Our feline friends are the reservoir for the most common form of ringworm in pets. Second in line is carried by rodents and picked up by nosy dogs digging through rodent burrows. The third form is a soil fungus.

It is possible to contract ringworm from your kitty. Studies show that in 30 percent to 70 percent of households where the cat has ringworm, at least one person will get it. However, humans have our own forms of ringworm. Athlete's foot is the classic example. Only 3.3 percent of all human cases are caused by the same fungus that infects dogs and cats, so you are far more likely to get ringworm from the playground or weight room than from your furry friends.

"People with the highest risk for catching ringworm from their pet are young children who have never been exposed, the elderly, or people with a depressed immune system," comments Dr. Angus. Once humans have been exposed to a strain of ringworm, most people develop immunity and rarely get the same strain again.

"It's important to know you have ringworm in your home. If your pet has patchy hair loss or any crusty bumps, take it to your veterinarian for a fungal screen. It is a good idea to screen all new pets, particularly strays, before introducing them to your current animals."

Your veterinarian performs a culture by plucking hair, growing the fungus, and identifying it under a microscope. Treatment needs to be aggressive. Generally a concert of topical dips or shampoos, clipping the pet's hair, and oral anti-fungals is prescribed.

"The anti-fungal drug of choice in dogs is Ketoconazole and in cats Itraconazole. Recently, the flea medication Program has been used to combat ringworm; however, current research shows that it is not effective against ringworm and should not be used as sole therapy," says Dr. Angus.

Treatment must continue until the culture results are negative, even though the animal may look better. Hair re-grows long before the fungus is exterminated. In a single-cat household, treatment can last 3 to 8 weeks and may be needed for longer periods in a multi-pet household.

Treating your home is also important. Fungal spores can persist in your carpet for up to 2 years, so re-infection is a concern. The more animals in the house, the longer the treatment must go on before the environment is clear.

"Hair is the enemy! Getting rid of the hair in your house is the best way to rid the fungus from your home. That's why we recommend that owners clip their animals' hair (making sure to warn the groomer). The only reliable killer of the ringworm spores is a 1:10 dilution of bleach in water. Use this with care because it is a harsh mix and will stain. Sunlight will kill ringworm too. Anything that can't be thrown away can be left outside to try to get rid of ringworm contamination," suggests Dr. Angus.

Fungus likes to grow in dark spaces on hair and debris. Your vacuum is a fungal mansion. If your pet has ringworm, change the bag each time you vacuum. The parts of a bagless vacuum can be soaked in diluted bleach water between uses.

If your pet has skin problems or you have questions about ringworm, please contact your local veterinarian.