Fungal Infection (Blastomycosis) in Dogs

Blastomycosis in Dogs

Blastomycosis is a systematic yeastlike fungal infection caused by the organism Blastomyces dermatitidis, which is commonly found in decaying wood and soil. Blastomycosis occurs most frequently in male dogs, but female dogs are also susceptible.

Dogs that are frequently exposed to environments where Blastomyces dermatitidisexists are at increased risk.

This is particularly so with large-breed dogs weighing at least 55 lbs (25 kg), and especially sporting breeds. The Blastomyces fungus thrives in wet environments, such as riverbanks, lakes and swamps, where damp soil lacking direct sunlight fosters growth of the fungus. It is also present in areas that are rich in decaying matter, such as wooded areas, forests, and farms. It is a naturally occurring North American fungus, with the highest prevalence of infection taking place in geographic areas located near water -- such as the Mississippi, Ohio, Missouri, and Tennessee River basins. Studies have concluded that most affected dogs live within at least 400 meters of a body of water.

The condition or disease described in this medical article can affect both dogs and cats. If you would like to learn more about how this disease affects cats, please visit this page in the PetMD health library.

Symptoms and Types

• Fever
• Loss of appetite (anorexia)
• Weight loss
• Eye discharge
• Eye inflammation, specifically the iris
• Difficulty breathing (e.g., coughing, wheezing and other unusual breathing sounds)
• Skin lesions, which are frequently filled with pus

Causes

Blastomycosis typically occurs when the dog inhales the airborne fungal spores of the genus Blastomyces dermatitidis after the contaminated soil has been disturbed. This can be from an activity as benign as digging in the dirt or following a scent trail. The spores can also enter through the skin. Exposure to areas with water, decaying matter, or recently excavated areas increase the risk of exposure to the fungus and consequent development of the disease.

Diagnosis

Care must be taken to test properly for this condition, since it is commonly misdiagnosed, which can lead to permanent or fatal damage. It may be mistaken for cancer and mistreated, or it may be mistaken for a lung infection of bacterial origin and treated with antibiotics, which puts your pet at greater risk. If your pet has been in an environment where the Blastomyces fungus may have been present, at any time in the six weeks previous to the onset of symptoms, you will want to ask your veterinarian to test for fungal infection.

The best methods for diagnosing blastomycosis is an examination of the cells in the lymph nodes, an analysis of fluid drained from skin lesions, a tracheal wash for collecting trachea (windpipe) fluids, and an examination of lung tissues. Tissue samples may also be taken to check for the presence of fungal organisms, especially if there is no productive cough (productive, meaning that fluids are produced). Other tests that may help diagnose blastomycosis include a urine analysis, and an X-ray of the dog's lungs.

Treatment 

Treatment is generally done at home, using oral dosages of an antifungal medication. The medication is relatively expensive and must be administered for a minimum of 60 days, or one month after all signs of blastomycosis have disappeared. Dogs with severe difficulty breathing (a condition known as dyspnea) may require an supplemental oxygen until lung condition has improved.

In severely prolonged infections, or when medication has not cured the infection, surgery may be necessary in order to remove part of an abscessed lobe in damaged lungs.

Living and Management 

Continue to give the necessary antifungal medication regularly and limit the dog's physical activities -- this will help it avoid straining its lungs. A high-quality diet to stimulate the dog's appetite is also encouraged. Chest X-rays can help determine the duration of and response to treatment, and reveal any permanent changes in the lungs that may have resulted from the treatment.

Although the disease is only spread from animals to people through bite wounds, humans may have been exposed to the Blastomyces organism at the same time as pets and should inform their physician if they have breathing problems or skin lesions, which are both good indicators of blastomycosis.

Prevention

This condition often is acquired in environments where decaying wood is found: farms, forests, wooded areas, camps, hunting areas. Decay of other organic material is also conducive to its growth in soil, especially when the soil is not exposed to sunlight and remains damp all the time.

Conversely, the spores may be more likely to go airborne during dry weather, when the contaminated dust is lighter. It is not easy to predict exactly where the Blastomyces organism may be growing, and is thus difficult to avoid entirely.

The only useful recommendation that can be given is to avoid lakes and streams where risk of exposure is greatest. This is, admittedly, an impractical suggestion for most. If you do live or spend time in these types of geographic areas, you may practicably be able to avoid the dense, dark areas where the fungus would thrive, reducing your pet's risk of exposure. As well, if your dog's immune system is already compromised, you will not want to include it in trips to high risk areas.

This condition is only rarely transmittable from animal to animal, or from animal to human. In the event that transmission does occur, it is when the animal has an open and draining wound, and it comes into contact with an open wound on the human, or the discharge from the animal's wound gets into the humans eye. Taking care to avoid these circumstances when caring for your dog will be sufficient prevention.