Skin Fungal Infections in Cats

What Are Skin Fungal Infections in Cats?

This type of skin infection is caused by fungi, which are parasitic, spore-producing organisms that are widespread in the environment. Fungal spores are very hardy and can remain in the environment for years. Cats pick up these spores from direct contact with an infected animal or directly in the environment, mostly through the soil.

Fungal infections can cause a variety of issues from skin infections to respiratory diseases. When the infective spores from the fungus contact the skin or nails of the cat, it can replicate.

Most healthy, adult animals have strong immune systems to fight off fungal infections, but stress, illness, and a weak immune system can predispose cats to getting fungal infections. Fungal infections take advantage of this weakness and invade the skin’s normally protective barrier. Skin fungal infections are more common in warm and humid conditions.

Many fungal infections are zoonotic, which means they can also infect humans. It is important to contact your health provider if your pet has been diagnosed or is suspected of having a fungal disease.

Types of Skin Fungal Infections in Cats

Dermatophytosis is the most common skin fungal infection in cats. These fungal infections are commonly called “ringworm.” Ringworm is not caused by a worm as the name implies, but by a fungus. A classic ringworm lesion involves a slowly expanding ring-like pattern of hair loss and scale, although this isn’t always the case. Some cats may have ringworm with no skin conditions or in other patterns of hair loss and scale.

Cats are usually infected with the fungus Microsporum canis, but other fungi include Microsporum gypseum and Trichophyton mentagrophytes. When infected, some cats may be asymptomatic carriers of ringworm and exhibit very few clinical signs, yet they are still capable of spreading the infection.

Other less-common fungal infections that infect the skin of cats include:

• Cryptococcosis: A fungal disease that may cause respiratory, nervous system, ocular (eye), and skin lesions. It is transmitted through the soil and in bird droppings, particularly from pigeons.

• Coccidioidomycosis: Also known as “valley fever” or “desert fever” it can be found in dry and semi-arid regions. Infections commonly occur after dust storms, heavy rain, construction, or earthquakes. This fungal infection typically causes systemic disease, but skin lesions include non-healing masses, hair loss, and draining wounds.

• Blastomycosis: This zoonotic fungal infection primarily causes respiratory and neurologic disease in cats, most notably pneumonia. Blastomyces can also look like skin masses and abscesses in cats. This disease is usually restricted to certain states around the Ohio River basin, the Great Lakes, and the St. Lawrence Seaway.

• Candidiasis: A fungal organism that is naturally found on the skin of a cat. Infections occur most commonly in association with immunosuppression.

• Malassezia yeast: A natural inhabitant of the skin that may cause overgrowth, especially in the skin and ears. Secondary to allergies, dermatological and endocrine conditions, it has been associated with some cancers in cats. Rex cats are predisposed to Malassezia infections.

• Cutaneous sporotrichosis: A zoonotic fungal disease that creates nodules (lumps) under the skin and draining wounds. A draining wound is an injury that penetrates the skin and usually the immediate tissue underneath, often forming tunnel-like lesions. It may be swollen, red, or infected and exude a discharge of blood or pus.

  • Male outdoor cats are most often infected due to increased roaming and exposure to contaminated thorns, splinters, dirt, and soil. It is also transmitted through fights with other cats. Sporotrichosis can also become systemic and affect the liver, lungs, and bone.

• Rhinosporidiosis: Typically, a disease of the nasal membranes, it can also infect a cat’s skin causing nodules or polyps with a stalk or stem.

• Phaeohyphomycosis: This is a group of fungal infections that cause skin masses and draining wounds around the paws, ears, and face. Occasionally, it can invade the nervous system.

• Mycetomas: An infection that causes skin or abdominal tissue swelling, a mycetoma will often produce a discharge that displays pigmented granules. These fungi are opportunistic and often infect cats after traumatic injuries, or through wounds from surgery.

Symptoms of Skin Fungal Infections in Cats

Fungal infections may be superficial, causing hair loss, redness, scaling, crusting, increased pigmentation, and pustules (bulging patch of skin). Infected hair follicles may be removed easily, but more severe fungal infections create under the skin nodules, draining tracts, and abscesses. Secondary bacterial infections are also common.

Many fungal infections are capable of invading the body causing a systemic disease that most commonly affects the lungs and the nervous system. Non-dermatologic clinical signs include:

• Fever

• Lethargy

• Breathing difficulty

• Coughing

• Weight loss

• Blindness

• Seizures

Causes of Skin Fungal Infections in Cats

Both pathogenic and non-pathogenic fungus is found commonly in the environment. The pathogenic, or disease-causing species, are usually found in soil, but can be spread through contaminated materials and other animals. Cats can get fungal infections through direct exposure, typically through the skin with a broken barrier, as well as breathing in or ingesting spores.

Fungi are opportunistic and take advantage of a host’s weakened immune system, wounds, and concurrent infections. Bacterial infections and fungal infections are often diagnosed together, although it can be difficult to figure out which came first.

While indoor cats can get fungal infections, outdoor, roaming cats have a higher exposure to fungal elements. Some cats may be asymptomatic carriers and show no symptoms, yet they can spread the disease to other animals and humans.

Longhaired cat breeds such as Persians and Himalayans may have a predisposition to skin fungal infections.

How Veterinarians Diagnose Skin Fungal Infections in Cats

Based on lifestyle and clinical signs of hair loss, crusting, and scaling, veterinarians may suspect a fungal skin infection. They may use a variety of tests to diagnose fungal infections as well as other common diseases (such as bacterial or parasitic infections) that show up similarly.

• Deep skin scrapes and cytology: While fungal structures are not commonly found during this process, skin scrapes and cytology are used to diagnose concurrent bacterial infections and mite infestations. Yeast infections also are commonly diagnosed with cytology.

• Wood’s lamp examination: Some types of fungal species will fluoresce bright green under this lamp, most commonly M. canis. However, it is possible to have false positives and false negatives, so the Wood’s lamp should only be used as a screening tool.

• Trichogram: In this test, a hair follicle and scale from the edge of a lesion is evaluated under a microscope for evidence of fungal structures.

• Dermatophyte culture: This is the gold standard of testing and involves taking samples of skin lesions and allowing them to develop on a growth medium for two to three weeks. Any growth is recorded and analyzed for species identification.

• Biopsy: Biopsy (removal of tissue for examination) may be best used in non-healing wounds and masses that are surgically removed.

• PCR: Some laboratories can run these tests to identify fungal DNA.

Treatment of Skin Fungal Infections in Cats

Surgical removal of nodules, draining tracts, and abscesses may be the preferred treatment method in some types of infection. All surgical lesions should be biopsied for a definitive diagnosis.

All concurrent illnesses—such as bacterial infections, allergies, parasitic infestations, or diseases causing immunosuppression—should be tested and treated as necessary.

Skin lesions involving scales, crusts, and hair loss are most often treated with oral anti-fungal medications such as Itraconazole, Terbinafine, and Fluconazole. Not all antifungals are safe in cats, so it is important to only use medications prescribed by your veterinarian. These drugs are typically given long term (over months) and require treatment for three to four weeks after resolution. Clinical resolution involves not only the disappearance of clinical signs, but also two negative fungal cultures.

Other animals in the house may also be treated to prevent asymptomatic carrier status.

Recurrences are common, and cleaning contaminated materials within the house is crucial. Bedding should be washed daily and areas difficult to decontaminate (such as carpet) should be avoided. Pet parents may wish to discard non-washable items, such as cat trees or toys, as they may be a continuous source of re-infection.

Topical antifungal therapy, such as lime sulfur dip or shampoos containing miconazole, are effective at eliminating spores on the hair coat and decreasing the spread of disease. Topical therapy is typically recommended throughout the entire treatment process.

Recovery and Management of Skin Fungal Infections in Cats

Overall, the prognosis for skin fungal infections is good to excellent. Pet parents should expect multiple re-check exams with the veterinarian throughout treatment. Cats are not considered cured until clinical signs are resolved and they have two negative fungal cultures. After this, treatment should continue for another month.

Causes of immunosuppression should be evaluated, including steroids, immunosuppressive drugs, and diseases such as cancer.

Most cats recover fully from fungal infections with time and treatment. Consistent treatment and thorough environmental decontamination are important for success. Relapses are common, so patience and commitment to a cure are vital for pet parents working with their veterinarians.