Ringworm in Cats

Jennifer Reding

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Diagnosis and Treatment

Ringworm is not a condition that the average cat owner in a dry environment like the desert often experiences, but because it can infect people, it is something that you should be aware of. But first, ringworm is not a worm—it is the common name for a fungal organism that infects the skin and hair of both people and animals. The organism causes a typical dry, scaly patch on the skin that is circular and often slightly raised around the edges, hence the name “ringworm.” There are several species of fungus that can infect mammals, but Microsporum canis (M. canis) is by far the most common to infect cats. In humans, ringworm is most likely to infect children, the elderly, and people with compromised immune systems.

In a healthy adult cat, ringworm is self limiting. Assuming that the cat is not reinfected (by another cat in the house), this cat is usually capable of clearing the infection on its own in 70 to 100 days. Unfortunately, in the meantime, the cat is infectious to everyone around them. Kittens, older cats, and cats with concurrent infections of any type (respiratory infections, ear mites, etc.) or parasites (fleas) are more susceptible to infection. In general, in a healthy cat, infection requires the presence of both spores and microtrauma on the skin as an opening to infection. A scratch, a flea bite, a clipper burn, or even rubbing an area can put skin at risk for infection.

The latest research suggests that a new infection becomes detectable in as quickly as 5 to 7 days and can become actively infectious before that. Spores are invisible to the naked eye, love to attach to hair, and tend to float like dust, making the environment around the infectious cat as important to treat as the cat itself. The developing infection causes hair loss and a typical round, dry, scaly lesion that grows out from the center. However, the infection can present in a variety of ways—it is often itchy, so some cats scratch bloody lesions; or, it may present as a crusty, dried-up sore. It generally presents on the face, ears, and feet, but lesions sometimes occur on the torso and the back of the neck.

So, you have a cat with a weird spot of hair loss or crustiness above his eye. Now what? The recommendation is to go to a veterinarian who has a Wood’s lamp (blacklight) with a magnifying element in it and has been trained to use it. On determination of the presence of a lesion, the recommendation is to perform a culture using DTM culture media, but there is also a ringworm PCR that can be run overnight. The PCR tests for M. canis DNA and is generally more expensive, but if time is of the essence, it is much faster than waiting 7 to 21 days for the DTM culture results.

The developing infection causes hair loss and a typical round, dry, scaly lesion that grows out from the center

The developing infection causes hair loss and a typical round, dry, scaly lesion that grows out from the center»

What do you do while waiting for the culture/PCR to come back? Isolate the suspect away from other cats, in an easily cleanable area, such as a bathroom. Start cleaning the house thoroughly with water and detergent—physical removal of spores is the most effective deterrent to the spread of infection. Can it go into the washing machine? Wash it. Either use bleach or, if you cannot use bleach, use the longest wash cycle on the machine and wash twice. Agitation is effective at removing spores.

So what if the PCR/culture is positive? Well, you have a lot of work ahead. Cleaning is going to be the hardest part. Clutter is your enemy. First, wash everything you can with detergent and then rinse well. Remember that spores float, and they love to float around on hair, so vertical surfaces need to be cleaned, too. Bleach is the most effective disinfectant at a 1:10 solution, but it is neutralized in the presence of organic material. Another effective disinfectant is accelerated hydrogen peroxide (AHP), sold under the brand names Accell and Rescue. (AHP is not the stuff you pick up at the grocery store in the brown bottle, so don’t use regular hydrogen peroxide.) The advantage of AHP is that it is not as harsh and can be diluted and sprayed on items that can’t be washed. You can also mop with it. Once you have the environment clean, the chances of contamination and infection of a non-infected cat are low. Most infections stem directly from an infected individual (although not always, obviously). But detergent neutralizes all disinfectants, so any surface cleaned with detergent needs to be rinsed well.

Once you have received the DTM cultures of your cat(s) (and don’t forget the dog—every hairy creature needs a culture), you can start on topical treatment. If you have a long-haired cat, it will be easier to treat if he or she is shaved down. The most effective topical treatment is lyme sulphur dip. All cats that are infected or possibly infected should be bathed with an antifungal shampoo and dipped in lyme dip at least once, and your vet may be willing to do that for you. In an environment like the desert, that may be all the treatment that you need for a healthy adult cat. You can also use OTC antifungal cream directly on lesions to help prevent continued spread.

Oral treatment may be recommended to treat infected cats. Itraconazole is the treatment of choice for infected cats, with terbinifine as a second choice. A commercial liquid is available that is 10 mg/ml, but if you have infected adults, having it compounded at a higher concentration (100 mg/ml) is easier. Once your cat stops showing outward symptoms, culture your cat weekly until you have two negative cultures, at which point you can stop treatment.

Again, if you live in the dry environment of the local deserts, it is less likely that you will encounter ringworm, but because it is zoonotic (transmissible to humans), it’s important to be aware of it and know how to treat it if you have pets.

Village Park Animal Hospital is located at 51-230 Eisenhower Dr. in La Quinta. Village Park Animal Hospital also offers grooming and boarding services for dogs and cats. (760) 564-3833 villageparkanimalhospital.com

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