Cryptococcosis in dogs: How to prevent and treat this fungal infection

Cryptococcosis is a potentially life-threatening systemic fungal infection. It can be challenging to both diagnose and treat due to the need for specific testing and long-term use of antifungal medications. It’s important to work closely with a veterinarian to accurately diagnose and appropriately treat canine cryptococcosis.

Inhalation of Cryptococcus spores is the main way dogs are infected, so you can minimize your dog’s risk by discouraging digging and sniffing in the soil, especially if you live in the Pacific Northwest or another area where the fungus is most commonly found (endemic). Because cryptococcosis is difficult to diagnose and treat, knowing more about the disease can help pet owners identify when their dog may have been exposed. Here, we’ll cover:

• Symptoms of canine cryptococcosis infections
• How cryptococcosis is diagnosed and treated
• What dogs are most at risk for cryptococcosis
• How owners can help prevent canine cryptococcosis in their dogs

Cryptococcosis spores are found primarily in soil containing decaying matter and bird droppings, with most infections in North America occurring along the Pacific coast and in the Pacific Northwest. Spores are ingested or inhaled, or get into an open wound, after which they can multiply and easily spread throughout the body. While the disease can affect any bodily system in your dog, the skin, eyes, and central nervous system are the most common.

Systemic fungal infections such as cryptococcosis are often challenging to diagnose because they’re less common than other conditions with similar symptoms and they require specific tests to identify the fungal organisms in the affected tissue. Cryptococcosis is treated with several months of oral antifungal drugs and supportive care.

Symptoms can become severe if the condition isn’t caught and treated promptly or if the dog has a lowered immune system. Avoiding risky behaviors that increase the likelihood of inhaling spores is the only way to try to prevent the disease, as there’s no vaccine or other preventative medication for cryptococcosis in dogs.

If you live in or travel through endemic regions, you can attempt to reduce your dog’s risk by discouraging digging in soil, avoiding areas with heavy bird activity (especially pigeons), steering clear of recently disturbed ground or decaying wood, and monitoring closely for early signs of illness. Talking to a veterinarian any time your dog shows new symptoms is important, even if those symptoms seem mild, because it helps identify the underlying cause early and ensures timely treatment. If your dog is showing mild signs of illness and you’re not sure if it’s an emergency, a virtual vet appointment is a convenient way to get more information and professional guidance on what to do next.

Cryptococcosis is a systemic fungal infection caused by two species of fungi from the Cryptococcus group (Cryptococcus gattii and Cryptococcus neoformans). A systemic fungal infection doesn’t stay in one part of the body; after entering the body, the fungus can spread through the bloodstream to different areas. With cryptococcosis, commonly affected body systems include:

• Brain and spinal cord (central nervous system)
• Eyes
• Lungs or nasal passages
• Skin

These disease-causing fungi are found worldwide in soil and bird droppings, especially pigeon droppings. In North America, the Pacific coast and Pacific Northwest are considered endemic areas because the fungus is established in the environment and infections occur more often in these places. Dogs are typically infected when they inhale Cryptococcus spores or, less commonly, by ingesting them or getting them in an open wound. Once inside the body, spores can begin to multiply and spread to other bodily systems.

Symptoms of cryptococcosis in dogs

Clinical signs of cryptococcosis in dogs vary depending on which bodily system(s) is involved. Commonly affected parts of the body include the skin, respiratory tract, central nervous system, and the eyes. However, spores can spread to nearly any part of the body, and multiple bodily systems are often affected. Symptoms are different depending on where the infection is.

Respiratory symptoms:

• Sneezing and coughing
• Nasal discharge
• Swelling over the bridge of the nose or nasal cavity
• Difficulty breathing

Eye symptoms:

• Loss of vision
• Red eyes or bleeding within the eyes

Neurological signs:

• Incoordination (ataxia)
• Seizures
• Head tilt
• Uncontrollable eye movements (nystagmus)

Other clinical signs:

• Skin lesions or ulcers
• Swollen lymph nodes

The central nervous system and respiratory tract are the areas most often affected in dogs.

Clinical signs that warrant immediate veterinary attention

Even though most cases of systemic fungal infections in dogs start with mild symptoms and come on gradually, cryptococcosis can sometimes cause sudden, severe symptoms. Indications of an emergency and the need for immediate veterinary attention include:

• Difficulty breathing
• Blue gums, tongue, or lips
• Collapse or loss of consciousness
• Seizures
• Sudden loss of vision
• Loss of coordination or difficulty walking

“Since the symptoms associated with cryptococcosis also occur with other, much more common illnesses, arriving at a diagnosis of cryptococcosis often takes time,” explains Dr. Jo Myers, a veterinarian on the Vetster platform. “Veterinarians usually begin with a broad work-up rather than first targeting fungal disease by starting with a history and physical exam, followed by baseline tests, such as blood work and urinalysis, to help narrow down the list of possible illnesses.” Initial testing may involve:

• Blood work
• X-rays
• Cytology of skin ulcers, nasal discharge, or spinal fluid

These types of diagnostic tests are very useful for narrowing down the root cause of a dog’s symptoms, but they don’t test for the presence of a systemic fungal disease such as cryptococcosis. While initial screening tests are an efficient way to find problems that are more common, they may only hint at the issue or help rule out other causes, one of which may be fungal disease.

Because cryptococcosis is rare compared to other conditions, your veterinarian may opt to first try treating a dog that has respiratory symptoms for a more common viral or bacterial infection to see if that works before taking a more aggressive diagnostic approach. Many bacterial and viral respiratory and GI infections are more common and more easily treated than systemic fungal infections.

The primary way cryptococcosis is diagnosed in dogs is through antigen detection tests, which detect proteins from the fungus in blood, cerebrospinal fluid, or other samples. In some cases, cytology of nasal discharge or tissue can directly reveal the organism.

Treatment for cryptococcosis involves the long-term use of antifungal medications. Treating a systemic fungal infection takes a long time, often six months or more. Because oral antifungal medications are much harder on the body than antibiotics and often cost more money, a veterinarian will confirm a systemic fungal infection before starting treatment. Depending on the dog’s symptoms, additional symptomatic care may also be recommended, including:

• Seizure medication
• Nutritional support
• Hospitalization for IV medications and fluids
• Oxygen therapy

Repeat antigen testing is often recommended, and relapse is common after treatment. Prognosis varies depending on how severe the condition is and which bodily system(s) is affected. Prognosis is more likely to be poor when multiple parts of the body are involved or when neurological symptoms are severe.

Because there is no vaccine or preventative medication for cryptococcosis, the most effective way to reduce risk is to limit time in higher-risk areas and discourage behaviors that might expose your dog to infection, such as digging in disturbed soil or exploring places with heavy bird activity. Within endemic regions, areas with heavy bird activity and recently disturbed soil or decaying wood are considered higher risk.

If you live in or visit these areas, you can lower the risk of exposure for your dog by:

• Not allowing your dog to dig or sniff in soil
• Avoiding construction sites and other areas with overturned soil
• Avoiding areas with a lot of pigeons

If your dog develops new signs of illness, seek veterinary care promptly and mention any travel or exposure in endemic areas. Early diagnosis and treatment improves outcomes and helps keep cryptococcosis from getting worse.

Since infection usually occurs when dogs inhale the spores, dogs with certain lifestyles are at more risk than others:

• Hunting dogs
• Dogs who hike, especially off-trail
• Dogs who enjoy digging in the dirt
• Dogs on farms or properties where pigeon droppings build up

Dogs with lowered immune systems are more at risk of developing serious illness after exposure to infective fungi. Cryptococcosis can not spread from dog to human or between dogs.

Cryptococcosis often begins with subtle, generalized signs of illness that can be attributed to some other, more common illness. An online vet can help by virtually examining your dog, discussing their symptoms, and talking about their medical and travel history in a convenient, at-home appointment. Your vet can then make a professional recommendation on what to do next. If your dog is exhibiting emergency symptoms, immediately call the nearest in-person veterinarian or emergency clinic for advice on what to do next.

How do dogs get cryptococcosis?

The fungi that cause cryptococcosis live in soil, decaying matter, and bird droppings. Many infections in North America are reported along the Pacific coast and in the Pacific Northwest. Dogs most often become infected by inhaling airborne spores from the environment, particularly in places with soil or decaying wood and where bird droppings (especially pigeons) are common.

What is the first line of treatment for cryptococcosis in dogs?

Cryptococcosis is a systemic fungal infection, so it’s primarily treated with the long-term use of systemic (as opposed to topical) antifungal drugs. Systemic fungal infections often take six months or more to fully treat, and relapse after treatment is common. In addition to antifungal therapy, your dog’s symptoms may also need treatment, which can vary depending on what the symptoms are.

Can I prevent my dog from getting a cryptococcosis infection?

There is no vaccine or preventative medication for cryptococcosis. Infection occurs when dogs inhale spores from the environment, so prevention focuses on reducing exposure. Risk is higher in areas where the fungus is more common, such as parts of the Pacific Northwest, where it’s established in soil, decaying wood, and places with heavy bird droppings (often pigeons). You can lower your dog’s risk by limiting their time in these settings, especially around tree hollows, wood piles, areas where birds roost, and recently disturbed ground, such as construction or logging sites. This reduces, but does not eliminate, the chance of infection. Dogs that dig or do a lot of nose-to-ground sniffing have more opportunity for exposure.

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.