Fungal Infections in Dogs

Aspergillosis is an infection caused by several species of Aspergillus fungus. Aspergillosis occurs worldwide and can affect almost all domestic animals as well as many wild species. It mainly starts as a respiratory infection but can spread throughout the body. Susceptibility to this infection varies among different species.

Candidiasis is a fungal infection that affects the membranes typically inside the mouth and nose, along with the skin and digestive system. In more serious cases, infection can spread throughout the body. It occurs worldwide in many animal species and is most often caused by the yeastlike fungus Candida albicans. This infection is rare in dogs.

Several factors can increase the risk of candidiasis, including damage to membranes in the mouth and nose, use of catheters, treatment with antibiotics, and diseases or drugs that suppress the immune system.

Signs vary and are often nonspecific, like diarrhea, weakness, or skin lesions.

An ointment or other topical antifungal medication is typically used for treatment. Your vet might also treat an infected dog with different antifungal drugs given by mouth or injected into a vein. Many dogs recover from localized candidiasis, although recurrence of infection is common. Prognosis for more severe candidiasis infections in the bloodstream or in organs is typically not as good.

Also see professional information regarding candidiasis.

Coccidioidomycosis is a fungal infection caused by Coccidioides immitis. It is found in the environment and is not contagious between animals. It is found mainly in dry, desert regions of the southwestern United States, including valleys of southern California, as well as similar areas in Mexico and Central and South America.

Although many animals, including people, can be infected, only dogs are seriously affected.

Infection occurs only by inhaling fungal spores carried in dust. Outbreaks can happen when rainy periods are followed by very dry periods, which can create dust storms that spread the spores through the air.

The disease is seen mainly as a long-term respiratory infection, but it can also spread throughout the body. In dogs, it especially affects the eyes, joints, and bones.

Signs of coccidioidomycosis in dogs vary depending on the organs involved and the severity of infection. These signs include:

• chronic cough

• loss of appetite

• poor body condition/weight loss

• lameness

• swollen joints

• fever

• intermittent diarrhea

• possible draining skin sores if skin becomes infected (but skin entry is rare)

Diagnosis is made via x-rays or CT scans and lab tests.

Many dogs exposed to these fungal spores don't show any signs and are able to clear the infection on their own.

If chronic respiratory signs develop or the infection spreads to multiple organs in the body, long-term antifungal treatment is required. When the infection is spread throughout the body, treatment typically lasts at least 6–12 months.

With treatment, recovery from the primary respiratory form of infection is usually good. However, with more widespread infection, outcome varies depending what organs are involved and on the severity of disease. In many cases, the outlook is guarded.

There is no known way to prevent the disease other than limiting a pet’s exposure to desert soil and dust in areas where the fungus is found.

Also see professional information regarding coccidioidomycosis.

Cryptococcosis is a fungal infection that can affect the respiratory tract (especially inside the nose), the nervous system (brain and spinal cord), eyes, and skin. It is caused by the fungi Cryptococcus neoformans and Cryptococcus gattii, which are found worldwide in soil and bird droppings, especially pigeon feces.

Infection occurs by inhaling spores spread through the air or through spore contamination of wounds. Animals and people with weakened immune systems are at higher risk.

In dogs, the infection often spreads throughout the body, commonly affecting the brain, spinal cord, or eyes. Signs depend on what area of the body is affected. Infection of the nervous system typically causes head tilt to one side, involuntary rapid eye movements, paralysis (inability to move) the muscles of the face that prevents blinking, poor coordination, moving in circles, and seizures. Eye problems can include bleeding and inflamed eyelids.

The disease can also involve the nasal passages and lungs and can spread to many other organs, including the kidneys, lymph nodes, spleen, liver, glands, pancreas, bones, digestive tract, muscles, heart, prostate, and tonsils.

Diagnosis is made using lab tests on samples from affected areas of the body or from secretions from the nose or eyes, as well as on urine, blood, or spinal fluid.

Treatment involves antifungal medications and often requires several months of therapy, depending on severity of infection and degree of spread. In some cases, surgery is used to remove lesions in the nose. The outlook is poor when involvement of the nervous system is widespread.

Also see professional information regarding cryptococcosis.

Geotrichosis is a rare infection caused by Geotrichum candidum, a fungus found in soil, decaying organic material, and contaminated food. It is also normally present in the mouth and digestive tract of people.

In dogs, this fungus can sometimes cause widespread disease throughout the body. Signs vary, depending on which organs are affected, and can include coughing, fever, loss of appetite, increased thirst, difficulty breathing, vomiting, and yellowing of the skin and membranes lining the eyes.

The disease can progress quickly and is often fatal.

Treatment with antifungal medications might be attempted in cases that have spread through the body, but it is usually not successful.

Histoplasmosis is a fungal infection caused by Histoplasma capsulatum, a fungus found worldwide in soil. It is especially common in areas with many birds and bats in the midwestern and southern United States, particularly along river valleys.

Infection occurs when spores spread in the air are inhaled. The primary infection sites are the lung and lymph nodes inside the chest, although the digestive system can also be affected in dogs. From the initial infection site, the fungus can spread through the bloodstream and reach bones, eyes, and other organs.

Signs vary, depending on which organs are involved, and are often nonspecific. In dogs, chronic digestive problems—especially diarrhea—are common. Other signs include weight loss that can become severe, coughing, fever, anemia (low red blood cell count), intestinal ulcers, and enlarged liver, spleen, or lymph nodes. Difficulty breathing, skin sores, joint disease, and eye problems can also occur. In severe cases, the disease can progress rapidly and cause death within 2–5 weeks.

Diagnosis is made by identifying the fungus under the microscope in body fluids or organ samples and sometimes involves testing blood, urine, or spinal fluid.

Treatment is challenging and requires long-term antifungal medication therapy along with proper nutrition, injectable fluid therapy, and antibiotic treatment of bacterial infections occurring at the same time. Therapy must be continued for months and can be expensive.

Also see professional information regarding histoplasmosis.

Mycetomas are infections of the skin that appear as nodules (knoblike growths) or tumorlike masses. When caused by fungi, they are called fungal mycetomas.

Most fungal mycetomas stay in the infected area beneath the skin, but some develop from deeper-seated fungal infections inside the abdomen. When the legs or feet are affected, the infection can sometimes spread into the underlying bone.

Diagnosis is made by taking a sample of the mass and identifying the fungus within it under the microscope. Abdominal mycetomas have a guarded prognosis because they tend to involve greater organ damage. Skin mycetomas are usually not life-threatening but can be difficult to treat.

Treatment can involve surgical removal of the growth, and in severe cases, even leg amputation. Antifungal medication has been reported as effective in only a few cases.

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North American blastomycosis is caused by infection with the fungus Blastomyces dermatitidis. In the United States, it is more commonly found in the Mississippi, Missouri, Tennessee, and Ohio River basins, areas around the Great Lakes and the St. Lawrence Seaway, and parts of the Pacific Northwest. The organism thrives in moist, acidic soil rich in decaying plant material and has also been found in bird and bat droppings.

Infection typically occurs when fungal spores are inhaled. In most cases, the infection begins in the lungs and can spread through the bloodstream, especially if the immune system is weakened. Primary skin infection can occur, but spread starting in the lungs is much more common.

Young male dogs, especially hunting dogs, are at higher risk due to increased exposure to contaminated soil. The severity and outlook for infected animals depend largely on how severely the lungs are affected. In dogs, the disease most commonly involves the lungs, as well as the eyes, skin, and bones.

Common signs include coughing, fever, tiredness, loss of appetite, and weight loss. Lung disease can also cause difficulty breathing and decreased ability to exercise. Enlarged lymph nodes can be present. Bone infection can cause pain and lameness. The disease can also affect the urinary and reproductive systems, leading to blood in the urine or difficulty urinating. If the eyes are affected, dogs can experience pain, light sensitivity, increased pressure inside the eyes (glaucoma), and even blindness. Skin sores can appear as multiple draining skin nodules.

Diagnosis is based on symptoms, imaging (from chest x-rays or CT scans), and identifying the fungus under a microscope or through blood or urine tests.

Treatment depends on how severe the disease is and aims to control symptoms and eliminate the fungus. Antifungal medications are usually required for at least 2 months until signs resolve. Infections can come back in some treated dogs, sometimes months or years later, but most dogs respond again to treatment.

The outlook is best when lung disease is mild, more guarded when lungs are affected moderately to severely, and poorest when the nervous system is affected.

Also see professional information regarding blastomycosis.

Oomycosis (also called pythiosis) is a disease caused by infection with Pythium insidiosum, which is a water mold related to algae (not a true fungus). It occurs in tropical and subtropical regions worldwide and in warmer to moderate areas of the United States. In dogs, it is most commonly seen in Southeast Asia, eastern coastal Australia, South America, and in the United States, especially along the Gulf Coast. In the United States, cases are most often seen in the autumn and winter.

Infection occurs when animals ingest spores in water. Pythiosis most commonly affects the digestive system in young adult dogs, especially Labrador Retrievers. The stomach and intestines are most often involved, although any part of the digestive system can be affected.

Affected dogs often have a history of partial blockage in their digestive tract and might have an abdominal mass that can be felt during a veterinary exam. Common signs include vomiting, weight loss, and decreased appetite. Weight loss can be severe, but dogs might not appear very ill until the disease is advanced.

Less commonly, pythiosis affects the skin and surrounding areas. Infection usually occurs through a wound that allows spores to enter the skin. Many affected dogs have a history of swimming or exposure to swampy or standing water. These infections result in rapidly growing, tumorlike nodules that don't heal. They are most often found on the legs, neck, near the tail base, or the skin between the anus and genitals, but they can occur anywhere on the body.

Lagenidiosis is a disease reported in dogs in the southern United States and caused by a Lagenidium water mold infecting the skin, the area beneath the skin, and sometimes multiple internal organs. It most commonly involves the legs, breasts, and skin between the anus and genitals or on the dog's chest and/or back.

In severe cases, the infection can involve internal lymph nodes, lungs, and large blood vessels. This can cause dangerous bulges in blood vessel walls (called aneurysms), which can burst, causing sudden death.

Dogs that are exposed to warm, standing fresh water are at higher risk, because they can come into contact with infectious spores. However, some infections occur in dogs without a known history of water exposure, suggesting that resistant spores in wet soil or grass might also be a source of infection.

Diagnosis is made using lab tests such as blood or organ cultures and blood testing. Treatment usually involves aggressive surgery to remove the infection, but complete removal is often not possible because the disease is already widespread at diagnosis. In some cases, amputation of affected body parts can be curative. Surgery is often combined with antifungal drugs.

Only about 20% of dogs respond to long-term antifungal therapy. Overall, the outlook is guarded to poor, although some dogs have improved with newer treatments such as therapeutic vaccines.

Also see professional information regarding oomycosis.

Phaeohyphomycosis is a general term for infections caused by various fungi in the family Dematiaceae that are found worldwide in decaying plants, soil, and water.

This infection is uncommon in dogs but can occur when the fungus enters the body through a wound. Signs more often occur in animals that are ill or have weakened immune systems and include skin nodules with ulcers (sores) and masses inside the nose or surrounding areas.

Slow-growing nodules or masses sometimes develop under the skin, especially on the head, legs, chest, or inside lining of the nose. In most cases, the infection remains limited to the skin and nearby areas.

Diagnosis is made by identifying the fungus in skin or fluid samples.

Treatment is often difficult. Surgical removal of the affected area, combined with antifungal medication, can be curative. If surgery isn't possible, antifungal drugs alone may be used. In animals receiving immune-suppressing drugs, the outlook might improve if those medications can be stopped.

Also see professional information regarding phaeohyphomycosis.

Rhinosporidiosis is a long-term fungal infection that mainly affects the lining of the nasal passages and sometimes the skin. It is caused by Rhinosporidium seeberi. The disease is uncommon in North America but is most often seen in India, Africa, and South America.

The infection causes growths like polyps that can be soft, pink, and crumbly with a rough surface. These masses can become large enough to block the nasal passages. Skin lesions are single or multiple and can be attached by a broad base or a narrow, stalklike connection.

Diagnosis is made by identifying the organism in samples from the affected area.

Treatment usually involves surgical removal of the lesions, but recurrence is common. The disease is usually not fatal.

Sporotrichosis is a sporadic, long-term infection caused by Sporothrix schenckii. This fungus is found worldwide in soil, plants, vegetation, and timber. In the United States, it is most commonly found in coastal areas and river valleys.

Infection usually occurs when the fungus enters the body through a skin wound, often after contact with plants or soil or from an injury that breaks the skin, like from a thorn or branch. In some cases, the disease can spread from animals to people.

The infection can stay limited to the skin at the entry site or spread to nearby lymph nodes. Early on, animals might not appear very ill, but over time they can develop fever, sluggishness, and depression. In rare cases, untreated or poorly treated infections can spread through the bloodstream to organs including the bones, lungs, liver, spleen, or the reproductive, digestive, or central nervous systems. When this occurs, the disease can become life-threatening.

Diagnosis is usually confirmed by culturing the fungus from affected areas. Treatment typically requires long-term antifungal therapy, continued for 3–4 weeks after dogs seem well.

Because sporotrichosis can be spread from animals to people, strict precautions are necessary when handling infected or suspected cases. If your pet is diagnosed with this disease, follow the vet's guidance carefully to decrease the risk of spread to other animals or people.

Also see professional information regarding sporotrichosis. 

• Also see professional content regarding fungal infections.