Blastomycosis is a fungal yeast-like infection caused by the organism Blastomyces dermatitidis, most commonly found in rotting wood and soil. Blastomycosis in dogs is fairly rare, but it can be potentially fatal.

The fungus grows in moist and decaying soil and vegetation, where it releases spores into the air. Those spores can then be inhaled by dogs or people, which will cause infection to ensue. Spores can also find their way into a dog’s system through open wounds. Once the pathogen has been inhaled into the lungs, the spores become much larger and grow much thicker walls. They also begin to multiply inside the lung and move to other tissues within the infected animal.

The symptoms of blastomycosis vary greatly from animal to animal, but the disease mainly affects the lungs and skin. In some cases the eyes, joints, and other organs can also be affected. In the case of ocular blastomycosis, permanent blindness can happen very suddenly. The infection unfortunately is very difficult to diagnose and if left untreated, it can even cause death.

Due to the fact that blastomycosis is a fungal disease, it thrives in wet environments where the soil is damp and there’s not significant sunlight to foster the growth of the fungus. Areas that have a lot of decaying matter such as wooded areas, forests, and farms, are also areas where blastomyces dermatitidis is likely to be found. Studies have shown that most dogs that become infected with blastomycosis live within at least 400 meters of a body of water.

Although female dogs can contract blastomycosis, it is much more common in male dogs. Larger, hunting breeds of dogs that weigh more than 55 pounds are also at increased risk. Dogs with compromised or weakened immune systems are also at much higher risk than healthy dogs.

Symptoms of Blastomycosis in Dogs

Blastomycosis is a chronic condition with symptoms that start off very mildly and gradually become more severe. Because the infection typically attacks the lungs and vascular system, the symptoms are often mistaken for pneumonia. If your dog’s symptoms persist, and especially if they become worse, it’s important to be persistent with your veterinarian, as early detection will greatly increase the chances of survival. The most common symptoms of blastomycosis are:

• Fever
• Anorexia or loss of appetite
• Weight loss
• Discharge from the eye
• Inflammation of the eye
• Infection of the eye, particularly around the iris
• Sudden blindness
• Coughing, wheezing, or other difficulty breathing
• Skin lesions, with or without pus
• Flu-like symptoms
• Lethargy
• Joint pain
• Loss of coordination
• Inability or reluctance to walk
• Swollen lymph glands

Diagnosing Blastomycosis in Dogs

There are several tests available to confirm the presence of the Blastomyces dermatitidis fungus, and they should be done if blastomycosis is suspected. Often the condition is misdiagnosed as cancer or pneumonia and afterwards, often antibiotics are prescribed for these conditions. This can actually make blastomycosis much worse, and can be potentially fatal for dogs.

You will want to speak to your vet about testing for fungal infections, especially if your pet was in an area where the Blastomyces fungus may have been present any time in the six weeks before the onset of symptoms.

Some of the most common tests performed when diagnosing blastomycosis are:

• Examination of the cells in the lymph nodes
• Analysis of fluid drained from skin lesions
• Tracheal wash for collecting fluids in the windpipe
• Examination of lung tissues
• Examination of tissue samples to check for the presence of the fungus
• Urinalysis
• Lung and chest X-rays

Treating Blastomycosis in Dogs

After the presence of the fungus has been confirmed and a diagnosis has been made, the vet will prescribe an antifungal medication. Just as the condition is chronic and develops over a long period of time, the medication must also be given over a long period of time, typically up to two months after all symptoms have disappeared. Blastomycosis is an extremely aggressive infection and as such, it must be treated just as aggressively. The medications are expensive, with the most common of them being:

• Itraconazole
• Amphotericin-B
• Itraconazole suspension
• Ketoconazole
• Fluconazole
• Posaconazole
• Voriconazole
• Prednisone

It’s important to remember that dogs may seem to become sicker right after they start taking the medication. This is because the drugs attack hundreds of yeast microorganisms and can really take a toll on the dog’s system. Even after treatment, some of the yeast may still remain in the body, meaning that relapses can occur.

Unfortunately, there is not currently a vaccination for blastomycosis and it can be difficult to determine if the fungus is present in surrounding areas because they live in the environment for such a short amount of time. The best prevention tactic for blastomycosis in dogs is being aware if the fungus is in your area, especially if it’s infected other animals, and being able to recognize the symptoms of the sickness. Like with so many other illnesses, early detection is critical to ensure that the dog’s condition does not become fatal.