Visiting Vet: Ringworm

It’s not a worm and it doesn’t make a ring.

In young animals, ringworm is often mild and self-limiting, but some cases become serious and a real headache to treat. —Pieter Lanser

Ben and Jerry, two kittens from Texas, recently arrived on the Vineyard. They had received good care prior to adoption, including feline leukemia (FeLV) and feline immunodeficiency virus (FIV) testing, first vaccinations, and deworming. Arriving at my office for introductory exams, I began with Ben, starting at his head and working my way back, nose to tail. Everything looked good. A little flea dirt. They’ll need flea control, I thought to myself, but healthy otherwise … except … what’s that? Just as I noticed the scaly patch on Ben’s foot, his owner piped up. “He’s got a little bald spot there that seems to be getting bigger.” Oh, drat.

Ringworm. It’s not a worm. It’s a fungus. There are many different species of ringworm, but all together they’re called dermatophytes, and infection is called dermatophytosis. When people get ringworm, it usually makes an itchy, red, scaly ring, like a worm burrowed beneath the skin in a circle. Hence the misnomer “ringworm.” In cats and dogs, however, it doesn’t make a ring, just a dry, scaly patch … exactly like on Ben’s foot. I sighed. In young animals, ringworm is often mild and self-limiting, but some cases become serious and a real headache to treat.

I grabbed my Woods lamp and turned off the room lights. Other skin diseases can mimic ringworm. One easy test is shining a special UV light on the lesion. In certain cases of ringworm, the area may fluoresce bright Day-Glo green; it depends on exact species and strain, and how long it has been growing. Ben’s spot did not glow in the dark. That was good, but I was still suspicious.

“We should take a culture,” I advised, plucking a few hairs from the margin of the patch and pressing them into a small tube of dermatophyte test media (DTM). I also opted for a “toothbrush” sample. Using a brand-new toothbrush, I gently brushed Ben all over, then added the collected fur to the DTM. “Now we see if anything grows,” I said. DTM has a special feature that helps veterinarians differentiate ringworm from other nonpathogenic contaminants that might grow. It turns red during a specified time if true dermatophytes are present.

“Ringworm can be contagious to people,” I warned. Both people and animals get infected by contact with fungal spores. It can take one to four weeks after exposure for skin lesions to appear. Where do these spores come from? Often from another pet. Animals can be asymptomatic carriers, having spores on their coats but without any symptoms. Spores of some dermatophyte species are found in soil. All these spores are very hardy and can persist for months to years in the environment, lingering in kennels, cages, and pet carriers, on grooming tools, clippers, blankets, combs, and brushes.

So why doesn’t every exposed critter get ringworm? First of all, the fungus can’t infect intact skin. There has to be a point of entry — something as simple as microabrasions from fleas, grooming, even playing. In most healthy adults, the immune system stops the fungus from growing, but young animals and children are more susceptible, as are the elderly and individuals who are stressed, in poor health, or immunosuppressed, including cats with FeLV or FIV, people with HIV, and those undergoing chemotherapy for cancer or immunosuppression for transplants.

I prescribed an antifungal lotion to apply twice daily, instructing the owners to wash well after handling the kittens, and to watch themselves for lesions. Ben’s DTM sat in my desk drawer. I checked daily. At week’s end, the tube was not red. Perhaps it wasn’t ringworm after all.

Two weeks later, at their next visit, Ben’s spot was clearing up nicely, but Jerry now had a lesion on his face above the eye. A classic ringworm location. Despite the negative DTM culture, I was convinced this was ringworm. Everything fit. Young animals. Contagious. Fleas causing microtrauma. Stressed by traveling from Texas. Typical lesions. It walks like a duck. It quacks like a duck. I advised a new DTM culture from Jerry be sent to the big reference laboratory. There the DTM could be incubated for three to four weeks under optimum conditions for fungal growth, better than my desk drawer. The moment anything sprouted, technicians could initiate identification procedures. I sent Jerry home with the same medication and caveats.

As Ben and Jerry mature and get healthier and less stressed, odds are their ringworm will resolve with topical medication and time. However, in some cases, feline dermatophytosis can become generalized, affecting large parts of the body. Persian cats are particularly susceptible to this … and it’s a big headache. A migraine headache. Treatment involves a combination of topical and oral medications plus environmental management, sometimes for three months or longer. First come whole-body lime sulfur dips once or twice weekly to kill spores on the fur. Cats love this. The dip smells like rotten eggs, and it stains stuff. Owners love this. Sometimes we try different medicated shampoos, but they are not as reliably effective. Long-haired cats may need to be shaved. Daily oral antifungal medications are also prescribed. Owners and cats love pills. These drugs can affect the liver, so regular blood tests are recommended. More fun.

Finally there’s aggressive environmental decontamination. Dust. Vacuum. Remove all hair from rugs, furniture, floors. Disinfect all surfaces, floors, carpets, exposed fabric, and pet bedding. Discard toys and scratching posts. Decontaminate upholstered furniture by steam cleaning or with chemical disinfectants that hopefully won’t destroy your lovely brocade couch. Repeat twice weekly. More often if you have multiple cats. Continue until all signs resolve and two weekly DTM cultures are negative for growth.

The good news is most cats get cured, if owners follow all these recommendations. Fortunately, Ben and Jerry appear to have the mild, self-limiting form, and are responding well to the antifungal lotion. I’ll bet you a pint of ice cream Jerry’s DTM culture comes back positive for ringworm. Oh, wait. The test results are in: I win. Make mine Coffee Heath Bar Crunch.