Systemic fungal infections in cats: Symptoms and treatment

Systemic fungal infections that affect internal organs and body systems are much less common than localized, superficial fungal diseases in cats. Systemic fungal infections are most commonly transmitted by the inhalation of infectious fungal spores, but infection can also occur when a cat ingests spores or when spores contaminate a skin wound. If you have a cat, read on to learn more about:

• The difference between systemic and superficial fungal infections
• Common types of systemic fungal diseases in North America
• How fungal diseases in cats are diagnosed and treated

Symptoms of systemic fungal infections vary widely depending on the type of infection, what part of the body is affected, and how severe the infection is. Clinical signs can include skin lesions, respiratory symptoms, loss of appetite, weight loss, neurologic symptoms, and many others. Treatment can be complex and usually involves antifungal drugs. Supportive care and surgical removal of skin lesions or growths caused by the infection may also play a role.

Fungi are spore-producing organisms found in the environment that can sometimes cause disease if a cat inhales, ingests, or touches them. Some fungal infections can cause disease in otherwise healthy animals, while others are more likely to do so in a cat that’s already sick, weakened, or immunocompromised.

Superficial fungal infections, such as ringworm, are localized to the outer layers of the skin, ears, nails, and mucous membranes. Fungal skin infections usually affect localized patches of skin but can also affect multiple areas. Systemic diseases, however, occur inside the body and can affect multiple organs, systems, or parts of the body, including the skin. Systemic fungal diseases in cats, though less common than superficial infections, are usually much more severe and can be life-threatening.

There are multiple systemic fungal diseases found worldwide that can affect cats. Specific diseases tend to occur more commonly in some regions than others (endemic diseases). The names of systemic fungal diseases typically come from the scientific name of the pathogenic fungus followed by the suffix “-osis.” The most significant fungal diseases that affect cats in North America are cryptococcosis, histoplasmosis, blastomycosis, and coccidioidomycosis, even though all are rare.

Cryptococcosis

Feline cryptococcosis is the most common systemic fungal disease seen in cats in North America. Cryptococcosis cases are most commonly reported along the Pacific coast, but they can also occur in other parts of North America as well as in parts of Europe and Australia. Cryptococcus spores are found in decaying vegetation and in bird droppings, especially from pigeons, and infection occurs when spores are inhaled.

Feline cryptococcosis primarily affects the nasal cavity due to it being an airborne disease, but it can spread throughout the body after spores have been inhaled. There are four forms of feline cryptococcosis, which can affect one or more parts of the body:

• Nasal, affecting the nasal passages
• Cutaneous, affecting the skin
• Neurologic, affecting the nervous system
• Systemic cryptococcosis, affecting multiple parts of the body

The nasal form of cryptococcosis is the most common form of the disease in cats. Cutaneous cryptococcosis usually occurs when the fungus spreads to the skin after entering through the nose. The neurologic form occurs when the disease spreads beyond the nasal cavity to the cat’s brain. Systemic cryptococcosis occurs when the fungus reaches the bloodstream, allowing the disease to spread throughout the body.

Though symptoms vary depending on the type of infection, they may include:

• Nasal discharge
• Loud breathing
• Sneezing
• Facial swelling
• Lethargy
• Loss of appetite and weight loss
• Nonhealing wounds on the skin and face
• Loss of balance or incoordination
• Behavioral changes
• Painless, non-itchy nodules under the skin
• Lymph node enlargement
• Sudden blindness
• Seizures
• Joint inflammation

Cats can have multiple forms of cryptococcosis as the disease spreads.

Histoplasmosis

Histoplasmosis is another significant systemic fungal disease in cats. Most cases occur in the central and southern United States, but the disease can be found worldwide. Infection occurs when Histoplasma capsulatum spores are ingested or inhaled. These spores are found in soil that has been contaminated with bird and bat feces. Common signs of histoplasmosis are usually vague and nonspecific and can include:

• Lethargy
• Weight loss
• Poor appetite
• Cough
• Difficulty breathing
• Skin masses
• Eye abnormalities

Blastomycosis

Blastomycosis is a systemic fungal infection found primarily in central, southeastern, and Great Lakes regions of the United States as well as in Canada in Quebec, Ontario, and Manitoba. Blastomyces dermatitidis spores thrive in wet, sandy, acidic soils rich in organic matter. These areas are often in valleys near water.

Infection occurs when cats inhale Blastomyces dermatitidis spores into their lungs. Clinical signs can take weeks to months to appear after exposure. Symptoms vary depending on which part of the body is infected but can include:

• Coughing
• Ulcerated or draining skin lesions (common in dogs; rare in cats)
• Neurologic signs, such as seizures and head tilt
• Difficulty breathing
• Eye problems and eye inflammation
• Nasal discharge, which may be bloody
• Lack of appetite
• Bloody urine (uncommon)
• Enlarged testicles (rare; intact males only)

Large skin lesions and neurologic symptoms are more common in cats than in either dogs or humans with blastomycosis infections.

Coccidioidomycosis (valley fever)

Coccidioidomycosis, or valley fever, is a dust-borne infection seen primarily in dogs in arid regions of the southwestern United States, Mexico, and Central and South America. Infections occur when Coccidioides immitis or Coccidioides posadasii spores are inhaled, especially in rainy seasons followed by drought.

Valley fever is uncommon in cats. When it does occur, it’s primarily a chronic respiratory infection, but it can affect the skin and other areas of the body. Symptoms can include:

• Skin lesions and abscesses
• Bumps under the skin
• Loss of appetite and weight loss
• Difficulty breathing
• Respiratory signs, such as coughing and sneezing
• Lameness
• Neurologic symptoms
• Changes to the eyes

Infection spreads to multiple bodily systems in approximately half of infected cats.

Clinical signs of systemic fungal diseases in cats vary widely and are similar to those seen in many other health issues, so a vet usually uses diagnostic testing to determine the cause of the presenting symptoms. Testing may involve:

• Physical examination
• Blood tests
• Urinalysis
• Neurologic examination
• Nasal swab fungal culture
• Diagnostic imaging, such as X-rays
• Tissue biopsy

“Some fungal infections can be challenging to diagnose because they present with nonspecific clinical signs, and definitive diagnostic tests, such as fungal cultures, can take time to yield results,” explains Dr. Jo Myers, a veterinarian on the Vetster platform. “Veterinarians may initially pursue treatment for more common conditions that share similar symptoms and only consider fungal diseases when patients fail to respond as expected.”

Once there’s a definitive diagnosis of a fungal infection, treatment options may include:

• Oral, topical, or injectable antifungal treatment
• Supportive care
• Surgery

Supportive care varies depending on which body systems are affected and how severe the infection is. It may involve additional medication, hospitalization, IV fluid therapy, and other treatment methods. Surgical removal of growths or lesions caused by the infection may be recommended.

The prognosis varies depending on the type of infection, the severity of the infection, which systems are affected, and the overall health of the cat. Cats with severe infections or who already have reduced immune function may have a poor or guarded prognosis.

The successful treatment of systemic fungal diseases is often more complicated than treating a bacterial infection. Prolonged treatment with antifungal medication over several months is often required, as opposed to antibiotic use for a couple of weeks for bacterial infections. Antifungal drugs can also be more expensive than antibiotics and may have a narrower margin of safety compared to antibiotics. Cats undergoing antifungal therapy may require ongoing blood work to monitor the liver and kidneys during treatment. It may take weeks to months to successfully treat a systemic infection. During this time, secondary infections may develop, especially secondary bacterial skin infections.

How common are systemic fungal infections in cats?

Overall, systemic fungal diseases are rare in cats, but they are more common in some geographical areas than others. Superficial fungal infections are much more common. Outdoor cats have a greater risk of infection due to increased exposure to bird and bat droppings, soil, and airborne particles that may contain fungal spores. However, it’s possible for indoor cats to be exposed to potentially infectious fungal spores through:

• Houseplant soil
• Airborne particles coming indoors, such as through open windows
• Soil carried in by people and pets that go outdoors

If you’re concerned about your cat’s risk of a fungal infection or need help administering medication for your cat’s infection, online veterinary professionals are available to offer advice and direction through virtual vet appointments.

How did my indoor cat get cryptococcosis?

Indoor cats with cryptococcosis may have been exposed to infective fungal spores from houseplant soil, airborne spores blowing through windows, or pets or people that go outdoors.

What is the most common systemic fungal infection in cats?

Systemic fungal infections are rare in cats in general, but cryptococcosis is the most common systemic fungal disease in cats in North America. Cats with cryptococcosis can show a wide variety of symptoms depending on which parts of the body are affected. In cats, the nasal passages and respiratory tract are most commonly affected.

How do you know if your cat has a fungal infection?

Fungal diseases in cats have a wide range of common symptoms, including patchy hair loss, skin lesions, coughing and sneezing, neurologic symptoms, nasal discharge, changes to the eyes, lethargy, loss of appetite, and many others. Signs of fungal infections can be similar to many other medical issues, so it’s important to talk to a veterinarian for an accurate diagnosis before attempting any form of treatment at home.

Disclaimer: This article, its content, and its related references do not constitute veterinary advice and should not be considered a substitute for veterinary care. If your pet is showing any symptoms that could indicate a medical emergency, please seek immediate emergency care.