Ringworm

One of the kittens a week ago, cute and almost ready to adopt out.

My wife’s cousin called me a few days ago and said she was raising a litter of stray kittens. Last week they were doing great and looked like they were almost ready to adopt out. But just when she was ready to turn them over to a rescue group, all four had suddenly developed patchy areas of crusty skin and hair loss. After a few questions, I confirmed what I think she was already thinking – they almost certainly had ringworm. What a disaster! The kittens were now not adoptable. Any treatment would be long and difficult. And worst of all, the kittens might have given her ringworm.

Interestingly, in spite of the name, ringworm is not caused by a worm, and rarely has a ring type appearance in pets. Ringworm is caused by a group of fungi called dermatophytes that feed on keratin in skin, hair, and nail tissue. We most commonly see ringworm in kittens, mainly strays that have been rescued. The typical appearance is patchy areas of hair loss with scaly skin especially around the head, face and feet. In some cases, the lesions are very difficult to notice, sometimes nothing more than a few broken off hairs.

The same kitten this week with hair loss and inflamed, scaly skin over the left eye.

Ringworm is very contagious, most often spread by direct contact with an infected individual. However, exposure to fungal spores and infected hairs left on furniture, floors or other surfaces can spread the fungus as well. One ringworm fungus, Microsporum gypseum, is usually contracted by exposure to affected soil.

Diagnosis can often be made by shining a black light over the suspicious areas. The most common ringworm, caused by Microsporum canis, will fluoresce an unmistakable bright green when present. Other species of fungal infections will not fluoresce and a culture of hair, skin, or nail tissue will have to be set up. After up to a week or more, a sample of the fungal growth can be taken and examined under the microscope to confirm the diagnosis.

Fortunately, although some fungal infections are notoriously difficult to treat, ringworm generally responds very well to treatment. Special dips, often with oral antifungal medications, are usually successful in clearing the infection. The dips have a very unpleasant odor, somewhat like rotten eggs, and must be allowed to dry on the patient leaving the bad smell both in the air and on the patient. These must be continued once or twice a week for several weeks. Although we rarely need to in kittens, in some severe cases of ringworm, clipping the hair is recommended to make the dip more effective. Response can be slow, often requiring 4-6 or more weeks of treatment.

Microsporum canis spores as seen when stained and viewed under a microscope

Ringworm is contagious to not only other pets, but also people. Extreme care must be taken when handling ringworm patients to avoid getting infected. While any age group can be infected, the fungus is most likely to spread to kittens, puppies, and children so extra precautions must be taken to keep ringworm patients away from the young. Adults, however, are not immune as I was reminded a few years ago. Washing your hands after handling ringworm is usually adequate, but apparently I missed a spot. Not long after treating a ringworm patient, I developed a beautiful example of the classic ringworm lesion on my hand. Topical treatment with an antifungal cream cleared it up, but it took close to a month to resolve. A reminder that wearing gloves is probably the smart thing to do around a known ringworm case.

Cleaning the environment is an important part of preventing the spread of ringworm. Once a pet had been diagnosed, the premises should be thoroughly vacuumed and cleaned of any possible infected hairs and fungal spores. This would include any areas the pet could have been, including floors, carpets, beds, and furniture. Treatment of outdoor areas is not generally useful unless there is maybe some patio furniture the pet could have lounged in.

A classic ringworm lesion on my hand a few years ago.

As previously mentioned, ringworm cases usually have happy outcomes if the patient is in good health otherwise. After our phone conversation, my wife’s cousin brought in her litter of stray kittens and when we put a blacklight on them they “lit up like a Christmas tree”, confirming ringworm. No further diagnostic tests were needed so we immediately started treatment. All four kittens were dipped in a Lime Sulfur dip and allowed to drip dry. They were started on generic terbinafine, an oral antifungal medicine for people but used commonly in animals. The cousin is now keeping them much longer than expected to continue the weekly dips and daily oral medicine until the kittens are free of ringworm and adoptable in a month or so. And fortunately, at least for now, she has not found any suspicious spots on herself.

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