Skin Fungal Infections in Cats

What Are Skin Fungal Infections in Cats?

Skin fungal infections in cats are caused by spore-producing fungi that are common in the environment. Cats usually become infected through direct contact with an infected animal or exposure to contaminated soil or surfaces.

When fungal spores reach the skin or nails, they can invade the skin’s protective barrier and cause infection—especially if a cat’s immune system is weakened. Stress, illness, and other health conditions can increase a cat’s risk of developing fungal infections, which are also more common in warm, humid environments.

Many fungal infections are zoonotic, meaning they can spread to humans. If your cat is diagnosed with or suspected of having a fungal infection, contact your healthcare provider for guidance

Types of Skin Fungal Infections in Cats

Dermatophytosis is the most common skin fungal infection in cats. This condition is 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, but this isn’t always the case. Some cats may have ringworm with no skin conditions or with 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 can affect a cat’s skin 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: A zoonotic fungal infection that 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: 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 surgical wounds.

Symptoms of Skin Fungal Infections in Cats

Skin fungal infections in cats can range from mild, superficial lesions to deep or even systemic disease.

Superficial infections may cause:

• Hair loss
• Redness
• Scaling
• Crusting
• Increased pigmentation
• Pustules (pus-filled bumps)

Infected hair follicles may be removed easily. More severe fungal infections can extend deeper into the skin and create:

• Nodules under the skin
• Draining tracts
• Abscesses

Secondary bacterial infections are also common and can worsen inflammation and discharge.

Many fungal infections are capable of invading the body and causing systemic disease, most commonly affecting the lungs and nervous system. 

Non-dermatologic clinical signs may include:

• Fever
• Lethargy
• Breathing difficulty
• Coughing
• Weight loss
• Blindness

Causes of Skin Fungal Infections in Cats

Skin fungal infections in cats are caused by exposure to pathogenic fungi in the environment.

Both pathogenic (disease-causing) and non-pathogenic fungi are commonly found in soil and organic material. The pathogenic species can also be spread through contaminated materials and other animals. 

Cats can become infected through direct exposure—most commonly when spores contact a broken skin barrier—but infection can also occur after inhaling or ingesting spores.

Outdoor and roaming cats have greater exposure to fungal spores, though indoor cats can still get fungal infections. Some cats may be asymptomatic carriers and show no clinical signs, yet they can still spread the infection to other animals and humans.

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

How Veterinarians Diagnose Skin Fungal Infections in Cats

Veterinarians diagnose skin fungal infections in cats using a combination of history, physical examination findings, and targeted laboratory tests.

Because bacterial and parasitic infections can look similar, testing is necessary to confirm the diagnosis and rule out other causes.

Common diagnostic tools include:

Deep skin scrapes and cytology: Although fungal structures are not commonly identified with these methods, they are useful for diagnosing concurrent bacterial infections and mite infestations. Yeast infections are also commonly diagnosed with cytology.

Wood’s lamp examination: Some fungal species—most commonly Microsporum canis—will fluoresce bright green under this ultraviolet lamp. However, false positives and false negatives can occur, so this test is considered a screening tool rather than a definitive diagnostic method.

Trichogram: In this test, hairs and scale collected from the edge of a lesion are examined under a microscope to look for fungal structures attached to the hair shaft.

Dermatophyte culture: This is considered the gold standard for diagnosing dermatophytosis. Samples from skin lesions are placed on a growth medium and monitored for two to three weeks. Any fungal growth is recorded and analyzed for species identification.

Biopsy: Tissue removal for microscopic examination may be recommended for non-healing wounds or masses, especially when surgically removed.

PCR testing: Some laboratories offer polymerase chain reaction (PCR) testing to detect fungal DNA, which can help identify specific fungal organisms more rapidly.

Treatment of Skin Fungal Infections in Cats

Treatment of skin fungal infections in cats depends on the type and severity of infection and often requires a combination of medication, topical therapy, surgical intervention (in some cases), and environmental control.

Any underlying conditions—such as bacterial infections, allergies, parasitic infestations, or diseases causing immunosuppression—should also be identified and treated.

Oral Antifungal Medication

Skin lesions involving scaling, crusting, and hair loss are most often treated with oral antifungal medications such as Itraconazole, Terbinafine, or Fluconazole. 

These medications are typically administered long term (often several months) and should continue for three to four weeks beyond clinical resolution. Clinical resolution includes not only the disappearance of visible lesions but also confirmation with two negative fungal cultures.

Not all antifungal medications are safe for cats, so only use drugs prescribed by your veterinarian. 

Topical therapy

Topical antifungal therapy, including lime sulfur dips or shampoos containing miconazole, helps eliminate spores from the hair coat and reduce transmission. Topical treatment is typically recommended throughout the entire course of systemic therapy.

Surgery

Surgical removal of nodules, draining tracts, and abscesses may be preferred for certain types of infection. All surgically removed lesions should be biopsied to obtain a definitive diagnosis.

Environmental control

Recurrence is common, so environmental decontamination is critical. Bedding should be washed daily, and areas that are difficult to disinfect—such as carpeting—should be avoided when possible. 

Non-washable items such as cat trees and toys may need to be discarded if they cannot be effectively cleaned, as they can serve as ongoing sources of reinfection.

Other animals in the household may also require treatment to prevent asymptomatic carrier status and reinfection. 

Recovery and Management of Skin Fungal Infections in Cats

The prognosis for most skin fungal infections in cats is good to excellent with appropriate treatment.

After clinical signs are completely resolved and two fungal cultures are negative, treatment should continue for an additional month to reduce the risk of recurrence.

Thorough environmental cleaning and strict adherence to the treatment plan are also essential for success.

In addition, underlying causes of immunosuppression should also be evaluated and addressed. This may include reviewing the use of steroids or other immunosuppressive medications and screening for diseases such as cancer.

Relapses are common, so pet parents should expect multiple recheck examinations with their veterinarian throughout the treatment process.