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Blastomycosis in Dogs

Dog near wooded river
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Severity: i High
Life stage: All

If you live in the mid-Atlantic, Great Lakes region, or along a major river in the central United States, you might be aware of the risk that blastomycosis poses to both pets and people. In some parts of the country, as many as 1-2 percent of pet dogs develop this condition every year, exhibiting a wide variety of clinical signs. 

Many cases of blastomycosis in dogs can be successfully treated. However, some pets will die of this disease, despite appropriate and aggressive treatment. Additionally, successful treatment is often prolonged and expensive. 

It’s important to be familiar with the risks posed by blastomycosis, because early detection can significantly improve your dog’s prognosis. 

What is Blastomycosis?

illustration of blastomycosis

Blastomycosis (or “blasto,” as it is commonly known) is a fungal disease. This condition is caused by a fungus known as Blastomyces. Blastomyces is found in moist soil and decaying organic material (such as rotting leaves and logs), and it can cause infections in humans, dogs, and a variety of other domestic and wildlife species.

In the United States, Blastomyces is most common in the Ohio, Mississippi, Tennessee, Missouri, and St. Lawrence River valleys; the Great Lakes Region; and the mid-Atlantic region. However, this fungus can be found in other areas of the Eastern United States, as well as in Canada and other countries.

What Causes Blastomycosis in Dogs?

Dog down by river

Dogs become infected by inhaling Blastomyces spores. Once these spores enter the lungs, they reproduce within the lung tissues and can spread to other parts of the body. The incubation period of blastomycosis can range from 1-3 months, which means that dogs may not show signs of blastomycosis until up to 3 months after exposure. 

Blastomycosis is most common in dogs who spend large amounts of time outdoors, sniffing the ground. Dogs that are most often diagnosed with this disease include young, male, large-breed dogs, such as a Hound, Pointer, or Weimaraner. Blastomyces exposure is most common in moist areas, near a body of water or after a heavy rain event. However, even small dogs in urban or suburban areas can be at risk. During dry months and during periods of high winds, Blastomyces can be stirred up from the soil (in dust) and become airborne.

Both humans and dogs become infected by inhaling Blastomyces spores in the environment. However, once infected, a human or dog is unlikely to spread this infection to others. There may be a small risk of transmission in the case of an immunosuppressed person or pet, but this infection typically occurs when fungal spores are inhaled directly from the environment and does not spread between people and pets. 

Symptoms of Blastomycosis in Dogs

Symptoms of blastomycosis in dogs include:

  • Cough
  • Shortness of breath
  • Fever
  • Weight loss
  • Lethargy

When Blastomyces spores are inhaled, they enter a dog’s lungs. The most common effect is a pulmonary infection, or infection of the lungs. This typically causes cough and shortness of breath. Many dogs also develop nonspecific signs of illness, including fever, decreased appetite, weight loss, and lethargy. 

Less commonly, blastomycosis may affect other organs. Potential alternative infection sites include the eyes, lymph nodes, skin, bones, urinary tract, nervous system, and heart. In these cases, signs will depend on the body system that is affected. For example, you may notice inflammation of the eyes, swollen lymph nodes, draining wounds, lameness, urinary signs, neurologic signs, or generalized weakness.  

Diagnosing Blastomycosis in Dogs

dog coughing outside

If you suspect your dog may have blastomycosis, it’s important to schedule an appointment with your veterinarian. 

Your veterinarian will first perform a complete physical exam, as well as screening blood tests. This exam and bloodwork will help your veterinarian look for indications of blastomycosis, as well as other illnesses that may be causing your dog’s symptoms. While it’s impossible to diagnose blastomycosis solely on the basis of an exam or screening laboratory tests, these are an important first step to arriving at a diagnosis. 

If your dog has signs of lung disease, your veterinarian will likely recommend chest radiographs (X-rays). Radiographs can help your veterinarian narrow down potential causes of your dog’s lung disease, helping them determine which tests should be recommended next. Blastomyces affecting other organs may require alternative tests. Your veterinarian may recommend radiographs if your dog is limping, biopsies of non-healing wounds, or aspirates of enlarged lymph nodes. 

Your veterinarian may send blastomycosis tests to an outside laboratory for analysis. Antigen tests, antibody tests, and PCR tests are often used to diagnose blastomycosis. While these tests each have their own unique limitations, interpreting their results in light of your dog’s clinical appearance and other findings can provide an accurate diagnosis. 

How to Treat Blastomycosis in Dogs

dog being treated for blastomycosis

Blastomycosis is a fungal infection and is treated with antifungal medications. 

The most common treatment for blastomycosis is itraconazole. This medication is typically administered for 2-6 months, with treatment continued for at least one month beyond complete resolution of clinical symptoms. A small percentage of dogs may experience liver effects with this medication, so your dog will be closely monitored by your veterinarian during treatment.

Less commonly, your veterinarian may prescribe fluconazole as an antifungal treatment. Fluconazole is better able to reach some organs that may be affected by blastomycosis, and it is easier on the liver. However, it can be less effective against blastomycosis and often requires longer courses of therapy. Your veterinarian will determine the best treatment for your dog, based on their history and clinical signs. 

In severe cases, your veterinarian may prescribe a short course of amphotericin B (a stronger antifungal). This will then be followed by a longer course of itraconazole or fluconazole. Your dog may also need steroids (such as prednisone) to provide short-term control of severe inflammation, or oxygen therapy to help with severe pulmonary signs. Eye drops may be required for blastomycosis affecting the eye, and blastomycosis affecting the skin may require bandaging and/or antibiotics. 

Prognosis for Dogs With Blastomycosis

If treated promptly and aggressively, roughly 75 percent of dogs will survive blastomycosis. However, the prognosis is worse if treatment is delayed or if a dog is severely ill at the time of diagnosis. 

Cost to Treat Blastomycosis in Dogs

Blastomycosis can be expensive to treat. Depending on how sick a dog is at the time of their first veterinary visit, initial testing and stabilization can cost approximately $500-$1,500. Antifungal medication and monitoring can cost an additional $300-$500 per month, for a period of 2-6 months. 

How to Prevent Blastomycosis in Dogs

There is no effective way to prevent blastomycosis in dogs. There is currently no vaccine that protects against this condition, nor is there a monthly preventative that you can give your dog. 

Limiting your dog’s exposure, by keeping them out of wooded areas near creeks and streams, may offer some theoretical protection. In reality, though, this is impractical and of questionable benefit. Remember, blastomycosis can become airborne on dry, windy days. 

Your best option, as a dog owner living in an area where this condition is prevalent, is to be familiar with the signs of blastomycosis. If your dog develops signs of illness – especially if they include coughing, shortness of breath, weight loss, anorexia, fever, non-healing skin wounds, or eye disease – seek veterinary care promptly. Early treatment can significantly improve the prognosis for blastomycosis.