Blastomycosis in Dogs

What Is Blastomycosis in Dogs?

Blastomycosis, sometimes called “Blasto,” is a systemic disease (a disease that can affect the entire body) caused by the fungus Blastomyces dermatitidis. The fungus is found in soil, where moisture and decomposing matter—such as leaves, feces, and other organic material—are commonly found. Because moisture is required for its growth, the fungus is commonly found in areas near water.

The fungus starts as mold in the environment and creates spores—tiny reproductive cells that can spread into the air. Spores release in the air whenever the soil they live in is disturbed. Spores can then be inhaled into a dog’s airways or embedded in the skin, where it can develop into blastomycosis.

The warmth of the host’s body allows the spores to transform into a budding yeast. The yeast colonizes the lungs or skin, and from there can spread to the bloodstream and infect other organs. The organs most likely to be affected are:

• Lungs/respiratory system

• Skin and subcutaneous tissue

• Eyes

• Bones

• Lymph nodes 

• Brain

• Testes

Less common targets are the prostate, liver, mammary glands, and heart.

As the disease progresses, the yeast colonizes and infects additional organs. Once three or more organs are involved, the dog’s prognosis is typically poor. If the disease is caught early and symptoms are mild, most dogs respond well to treatment. 

Symptoms of Blastomycosis in Dogs

The signs of blastomycosis are dependent on which organs are involved. In about 85% of cases, affected dogs first have a dry, harsh cough. In as many as 50% of cases, they will have skin nodules with pus. Owners of dogs visiting or living in areas close to water should watch out for the following symptoms:

• Respiratory issues, including coughing, difficulty breathing, and nasal discharge (especially bloody nasal discharge)

• Draining skin nodules/lesions

• Fever

• Swollen lymph nodes

• Weight loss or lack of appetite

• Eye issues, such as inflammation, blindness, or swelling

• Urinary issues, including bloody urine, difficulty urinating, or enlarged testicles in males

• Neurological signs, such as head tilts and seizures

• Lameness/limping 

In most cases, skin lesions and respiratory problems are the earliest symptoms of blastomycosis in dogs.

Causes of Blastomycosis in Dogs

Blastomycosis typically occurs when soil contaminated with the fungus is disturbed, allowing airborne spores to be inhaled by the dog. Sporting or hunting dogs are at an increased risk, as they are more often in these contaminated areas. In addition, the spores can enter through the skin. Areas that consist of water and decomposing matter, or were recently disturbed due to construction, increase the risk of exposure to the disease. 

How Veterinarians Diagnose Blastomycosis in Dogs

A complete physical examination with a detailed history is helpful for diagnosis of blastomycosis. It can often be mistaken for other conditions, so it’s important for a vet to rule out any other common conditions during diagnosis.

 Your veterinarian may start with the following:

• Blood tests

• Imaging (radiographs, ultrasound, or CT scan) to examine the lungs

• Urinalysis to look for yeast

• Cultures

• Serology

• Biopsies

Definitive diagnosis can be obtained by finding the organism in tissue, or through biopsies or an aspiration from skin lesions. (An aspiration is when a small sample of an area is collected through a needle and sent out for further analysis.)

It’s important to provide your veterinarian with any information about where your dog has been, in case it’s an area of high-risk for exposure. Be sure to mention any recent vacations or trips with your pet.

Treatment of Blastomycosis in Dogs

Antifungal medications are typically prescribed for blastomycosis and are given orally. They often must o be given for several months, but your dog can be treated at home if the illness is not severe.

Dogs with difficulty breathing may require oxygen therapy and hospitalization until they improve. In severe cases, or when medication does not work, prolonged hospital stays, intravenous medications, and further care may be required.

Dogs whose eyes are severely affected may not respond well to treatment and may require topical medications. If significantly affected, the eye may need to be surgically removed.  

Recovery and Management of Blastomycosis in Dogs

There is no way to prevent blastomycosis, aside from avoiding high-risk areas where the fungus may be  present. The prognosis for most dogs is positive, if treatment is provided as soon as symptoms start and medication is given correctly.

Pets with severe lung disease may appear worse at the beginning of treatment because the fungal organisms are dying. They may not improve for one to two weeks after the start of treatment, and so close monitoring should be done during this time, regardless of any additional underlying condition.

Once the organism affects the brain, seizures are common and may be uncontrollable. Dogs with brain involvement often die, and if more than three body systems become involved (meaning the disease has spread), the prognosis is typically poor.

Relapse can occur in dogs with very severe cases of blastomycosis or those for whom treatment was stopped too soon. These relapses are most common within the first 6 months after treatment.

It is unlikely that once recovered from the disease, the dog will be completely immune. Routine veterinary appointments, including annual exams, are critical to ensure the health and safety of your pet.

Blastomycosis in Dogs FAQs

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