Ringworm in Cats

Claire Dunling

When is a worm not a worm? When it is a fungus. If this fungus causes circular sores, naturally you’d call this condition ringworm. Originally it was thought the lesions were caused by a worm burrowing under the skin and feeding. Both the condition and name persist to this day.

Worm or fungi? Either way, it still matters

Despite the name, ringworm isn’t really a worm at all rather it is a fungal infection of the outer layers of the skin, nails and hair. This fungal infection is known as dermatophytosis and occurs in cats, dogs and humans. The key cause of the infection is a basket of various Microsporum. Luckily this alphabet soup has been simplified into far more comprehensible “ringworm”.

One type (species) of dermatophyte called Microsporum Canis, is responsible for almost all cat ringworm infections. A less common offender is trichophyton mentagrophytes. Both of these species are zoonotic, meaning that they can also infect humans and other pets.

What does ringworm in cats look like?

The most common clinical signs of ringworm in cats is patches of alopecia or hair loss. This is caused by the infected hairs becoming fragile or brittle and simply breaking off. Typically feline ringworm becomes apparent when you spot patches of missing hair or scaly, crusty, or red skin.

How do vets diagnose ringworm in cats?

Having such ‘obvious’ symptoms does mean that cat ringworm infections are usually straightforward to diagnose – mostly it is a case of ruling out other possible causes of hair loss. There is a quick test for microsporum canis and that’s to examine affected hairs under ultra-violet light, which causes them to emit a yellowy green fluorescence. However not all dermatophytes are so helpful and other substances can contaminate the test, so while this test is helpful it is not definitive.

Full diagnosis is made by microscopic examination of infected hairs and/or a culture of the fungus on them. So while the initial visual examination is relatively quick, the culturing can take up to three weeks.

Just because the symptoms start to improve don't stop the treatment! Ringworm can take months to clear up. Keep going until the vet says "stop"
John Campbell, Head Vet of Pet Drugs Online

Treatment of ringworm in cats

In many cats, ringworm is a self-limiting infection and will end in 4-5 months if the cat is left untreated. Any diagnosis though will result in treatment, simply to make sure that it does not spread to other cats or vulnerable humans – namely children.

There are two principal treatments for a cat with ringworm: topical and systemic drugs. Topical therapy simply means the application of a cream, ointment or shampoo. Systemic therapy means that you give them anti-fungal drugs by mouth – vets just love to give everything complicated names – usually both approaches are used in parallel.

Also, though not exactly a treatment, you will also need to clean the cat’s living space as it is very likely to be infected.

Treating ringworm in cats

If you’re told that topical therapy is to be part of the treatment it can involve putting cream/ointment directly on the affected areas. The most difficult (in a practical sense) is the use of shampoos, as few cats enjoy being bathed. During all topical treatments please follow the vet’s guidance on how to handle your cat bearing in mind it may still be infectious.

If you have to give your cat anti-fungal drugs, it is important to understand that some cats respond far better than others. So even if your cat’s ringworm appears to clear up, do not stop too early. Treatment will be for a minimum of six weeks, and in some cases much longer. The vet will also ask if there is more than one cat in the household, to keep them separated. This is practical as it will stop cross-infection, but can prove impractical in small modern homes. The alternative is to treat them all at the same time. You and your vet will have to decide, but be honest about your chances of keeping the cats apart.

Cleaning the house is a vital part of the treatment. Any infected hairs that have been shed into the environment will contain fungal spores. So infection can occur not only by direct contact with the ringworm visible on the cat’s skin but also through the contact with fungal spores. As a result you’re going to have to do a lot more cleaning, to keep the number of spores to a minimum.

Think about transferring the affected cat to a room that is easy to clean (fewer soft furnishings and harder floors) although this seems a little harsh it is ‘being cruel to be kind’ as they stand chance of recovering faster and better. You will need to thoroughly hoover any area the cat visits. Disinfecting any areas your cat has direct contact with a wash of diluted bleach would be ideal but may not be that practical.

Will my cat recover from cat ringworm?

With appropriate treatment the huge majority of cats will beat their ringworm infection in a few weeks. Some lesions may not change much during the first week, but obvious improvement will be seen within 3 weeks.

The risk to humans

Feline ringworm can quite readily be transmitted humans, especially children. So when the cat is diagnosed you’ll need to start the cleaning program described above. If any humans in the house develop small patches of skin thickened or red blotchy skin, or patchy of hair loss see you doctor immediately.

This post is an opinion and should only be used as a guide. You should discuss any change to your pet’s care or lifestyle thoroughly with your vet before starting any program or treatment.

If in doubt contact your veterinary practice

And always keep your vet's phone number handy - just in case!