What to Know About Fungal Skin Infections in Cats
Itchy and definitely not fun – here’s what to look out for
Healthy cats take great pride in their coats, grooming until every hair is shiny and slicked into place, like a kitty Bella Hadid. Sometimes a blemish appears and disrupts that sleek silhouette. Fungal skin diseases are an important cause of skin problems in cats, and some can even be transmitted to people. Differentiating fungal skin lesions from other skin lesions can be challenging, but it’s always best to know what to look out for.
Fungi that cause skin infections in cats can come from other cats, the soil or the yeast that are part of their skin’s normal flora. A cat’s breed, local environment and immune status will affect which fungi can cause problems for them.
What are some common causes of fungal skin infections in cats?
Ringworm
Despite its name, ringworm is not caused by a worm at all. In cats, it is caused by one of a few different fungi. The most common agents are Microsporum canis, Microsporum gypseum and Trichophyton mentagrophytes. Ringworm is usually transferred directly from one infected animal or person to another through contact with an open lesion, though contact with contaminated soil or bedding can also cause an infection.
Ringworm lesions develop one to three weeks after exposure and usually appear as crusted, scaly, reddened, hairless areas. They are often circular and surrounded by broken, brittle hair. Early lesions commonly develop around the face, then spread to the paws and the rest of the body. Most animals seem to find them pretty itchy. Persian cats may develop nodules beneath their skin instead of the usual flat spots.
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The most common way to diagnose ringworm is through a fungal culture. The sample is collected by brushing the cat’s hair (often with a brand-new toothbrush) before applying the brush to a fungal growth medium.
Some dermatophytes (especially Microsporum canis) fluoresce under a Wood’s lamp, which emits long-wave ultraviolet (UV-A) light. While this is a handy screening test, it doesn’t rule out or diagnose ringworm definitively because there are a lot of things that can cause false positives or false negatives.
In otherwise healthy animals, ringworm will usually go away on its own over time, but treatment is recommended to speed resolution because it is contagious to humans and other animals. The majority of vets recommend against showing up to a date with a fungal infection from your cat. Treating ringworm in cats ideally combines a topical agent like an anti-fungal dip or shampoo with an oral antifungal.
Environmental decontamination can reduce the spread of this disease and help to prevent reinfection. Remove all visible hair and skin flakes by hoovering and brushing surfaces. Depending on the home environment, it might be best to steam-clean furniture and carpets. Clothes and other washable materials can be washed with a diluted bleach solution.Fungi grow slowly and die slowly. Treatment takes weeks to months to fully resolve almost any fungal infection, including ringworm.
Malassezia dermatitis
Malassezia are a normal part of the microbiome of a cat’s skin. These yeast organisms can sometimes overgrow and cause itchy, flaky skin. This is often accompanied by a greasy, reddish-brown discharge or discolouration of the skin.
This type of overgrowth can be seen in cats who have compromised immune systems, such as those with feline immunodeficiency virus, feline leukaemia virus, diabetes mellitus, cancer or other health issues. Hairless cat breeds, including the Sphynx and Devon Rex, may be predisposed to a generalised dermatitis, while very hairy cat breeds, such as Persians and Himalayans, can to get yeast dermatitis in their facial folds.
Malassezia dermatitis is treated with topical therapies because the yeast lives on the surface of the skin. For generalised conditions, a topical shampoo is often needed. Some cats with very localised problems respond well to spot treatment with medicated wipes.
What are some uncommon fungal skin infections in cats?
Outdoor cats get exposed to a wide variety of pathogens as they explore and hunt. Some of these environmental exposures include fungi that can cause some pretty obscure diseases.
Cryptococcosis
Cryptococcosis is an infection caused by the environmental fungi Cryptococcus neoformans and Cryptococcus gattii. These fungi are found in places contaminated with pigeon droppings, decaying organic matter, and occasionally certain types of soil. Cats usually become infected when they inhale fungal spores, which settle in the nasal cavity.
The most common outward sign is a firm swelling over the nose or nasal bridge, sometimes giving a slightly ‘Roman nose’ appearance. The skin on the nose can become hairless, ulcerated or distorted, and many cats also develop sneezing, nasal discharge or visible difficulty breathing through the nose.
In some cases, the infection can spread beyond the nasal cavity. This may lead to skin nodules or ulcers, eye problems (such as cloudiness or changes in the retina) or neurological signs if the fungus reaches the brain or surrounding tissues. Widespread lumps all over the body are not typical of cryptococcosis.
Diagnosis is often made using a combination of blood tests, cytology, and occasionally, imaging. Treatment usually involves long-term antifungal medication, and many cats respond very well, especially when the disease is detected early.
Sporotrichosis
Sporotrichosis is an infection caused by fungi of the Sporothrix species. It is extremely rare in the UK, but isolated cases can occur, particularly in animals that have travelled or been imported.
Cats typically develop firm skin nodules at the site where the fungus enters the body. Over time, these nodules can soften, ulcerate and begin to discharge. In more advanced cases, the infection may spread along the lymphatic vessels, leading to multiple lesions or, occasionally, more widespread (systemic) illness.
Infection usually happens when fungal spores are inoculated under the skin, often through a small wound or puncture contaminated with organic material such as soil or plant matter.
In humans, a related infection is sometimes referred to as ‘rose gardener’s disease’ because rose thorns can effectively push fungal spores beneath the skin. While the name is commonly used in people, it is not a term generally applied to cats in UK veterinary practice.
Diagnosis relies on cytology, biopsy and fungal culture, and treatment typically involves prolonged antifungal medication. Most cases respond well when identified early.
Blastomycosis
Blastomycosis is caused by Blastomyces fungi, which are found in soil in certain parts of North America, particularly in areas near waterways. The disease is not present in the UK, but occasional cases may be seen in cats that have travelled or been imported from endemic regions.
Infection occurs when fungal spores are inhaled, allowing the organism to establish deep within the lungs before spreading through the bloodstream to other organs. Affected cats may develop a range of signs, including respiratory illness, weight loss, eye involvement and skin lesions. The skin changes can vary from small firm nodules to larger ulcerated lesions that resemble abscesses.
Blastomycosis is a serious, potentially life-threatening systemic disease, and prompt diagnosis is essential. Diagnosis typically involves cytology, biopsy, imaging and fungal culture. Treatment requires long-term antifungal therapy, and prognosis depends on how early the disease is identified and how advanced it is at the time of diagnosis.
Can people get fungal diseases from cats?
People can get ringworm from direct contact with an infected cat. Cats infected with Sporothrix can also transfer it directly to humans through cat scratches; this is an ongoing problem in Brazil and may be spreadingopens in new tab. Though humans are also affected by cryptococcosis and blastomycosis, the form that infected cats carry cannot be transmitted directly to people. Either way, it’s smart to practise good hygiene and wash your hands after handling any cat, especially one with skin lesions.
