October 23, 2019 Cats Dermatology

Ringworm is not a worm, but it’s a serious problem for your cat

Ringworm on the ear of a cat

Ringworm is not a worm, but it’s a serious problem for your cat

Medical terms can be challenging for non-medical folks to understand. Even medical terms that sound simple can be misleading for reasons that are hard to explain. The skin disease “ringworm” or dermatophytosis fits that bill.

Not worm, but is sometimes a ring

Ringworm is a fungal infection of the skin, not a worm infestation. I suspect the name comes from the appearance of the skin lesions on humans. Ringworm in people causes a circular, red rash on the skin, and I can attest to the fact that the rash is really itchy. A variety of different fungal organisms are responsible for causing ringworm, depending on whether you are a dog, cat, cow or human. In dogs and cats, the most common organism is Microsporum canis. As you can see from the photo above, ringworm in cats doesn’t form a ring.

Scaly, crusty, greasy

In my trusty feline medicine textbook, you will find ringworm classified under scaly, crusty and greasy skin diseases. Since ringworm is one of the most common skin diseases in cats and can be spread to both feline and human family members, any cat with skin issues becomes a ringworm suspect because of its infectious nature. Kittens, and especially shelter kittens, are susceptible to ringworm.

Is it ringworm?

Veterinarians have several different tests available to diagnose ringworm. During an initial examination, we use a Wood’s lamp (medical blacklight). Hair infected with ringworm glows lime green under a Wood’s lamp. This is a good screening test, but it’s not 100% accurate. The confirmatory test involves sending hair to the laboratory and growing the fungus in a special tube. This test takes a couple of weeks, which slows the diagnostic process. Recently, a new test has been developed to identify the presence of ringworm DNA in hair. This test gives results in a few days rather than in weeks. I typically send samples for fungal growth and DNA testing in cats I suspect as having ringworm.

Treatment is a pain

The diagnosis of ringworm sets off a cascade of treatments. Human family members need to see their dermatologist because cats readily give ringworm to humans. The home needs treatment because the hair carries the infectious fungus. If you have a cat, you know their hair is in the sofa, on the floor and floating in the air. Treatment needs to rid the environment of hair. Last, but not least, the infected cat and any other felines in the home must be treated.

Treatment of cats with ringworm must be more than just an antifungal crème. The entire cat must be treated, either with oral medications or bathing followed by an antifungal leave-on rinse. The most notorious of these antifungal rinses is lime sulfur dip, which is bright yellow and smells like rotten eggs. Despite the staining and smell, it’s very safe and works well. To see how a bath and rinse works in a cat with ringworm, watch Elizabeth’s spa day.

Ringworm is an annoyance for the cat and the cat’s family, but with collaboration between the veterinarian and the family, ringworm can be treated successfully. Recently, a less optimistic report from the University of New Hampshire described a fatal outbreak of ringworm in New England porcupines.