In a way, we’re thankful many of our readers have never heard of blastomycosis, assuming this is because your dog or others in your area haven’t been infected. If that’s the case, consider it a blessing—often, diagnosis of this fungal infection doesn’t end well.

My plan here is to help better inform us all on blastomycosis. To help us gain understanding, I’ll be asking my friend Dr. Jennell Appel, for insight. Dr. Appel has been involved in the field of canine rehabilitation since 2002, with a special interest in canine athletics.

Q. What is blastomycosis and why does it pose a danger to dogs?

A. Blastomycosis, sometime called “blasto,” is a fungal disease caused by Blastomyces dermatitidis. Infection with Blastomyces occurs when a dog inhales the fungal spores. The incubation period is from 5 to 12 weeks, which means that some dogs will not exhibit clinical signs of illness for a long time after being infected, but they are not contagious to other animals and people.

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 or embedded in the dog’s skin, where it can develop into blastomycosis.

The fungus most commonly infects our dogs through their respiratory tract. When the fungal spores are inhaled, they settle in the small airways and begin to reproduce. The organism then can eventually spread to the lungs and throughout the body to infect other organs.

In the United States, the fungus mainly lives in the mid-western, south-central, and south-eastern states, particularly in areas surrounding the Ohio and Mississippi River valleys, the Great Lakes, and the Saint Lawrence River.

Q. Are dogs more likely to encounter Blastomyces dermatitidis during the summer?

A. Yes, this could develop into blasto through a process where 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.

Q. What are the early symptoms of “blasto” (blastomycosis)?

A. The signs of blastomycosis are dependent on which organs are involved. In about 85 percent of cases, affected dogs first have a dry, harsh cough. In as many as 50 percent of cases, they will have skin nodules with pus. In most cases, skin lesions and respiratory problems are the earliest symptoms of blastomycosis in dogs. 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

Q. Does blasto affect all dogs that are exposed?

A. Well, thankfully most of our normal healthy dogs work in similar areas year after year without becoming infected, yet we do not know and cannot say they have any sort of immunity or ability to ward off blasto. I think we only know for sure that dogs with compromised immune systems are more predisposed to infection.

Another positive is for those found infected and caught early, the prognosis for many is good, with 50 to 75 percent of affected dogs recovering when treated with itraconazole, fluconazole, or an amphotericin-ketoconazole combination. At the same time, dogs with severely affected lungs or three or more body systems involved, have a guarded prognosis, but if the dog survives the first 7 to 10 days of therapy, recovery chances improve significantly. Relapses are most likely to occur in dogs that had a severe case at onset, or dogs that were not treated long enough. Relapses are most common within the first six months after treatment. Unfortunately, dogs that recover from the disease are not immune to infection in the future.

After discontinuing therapy, dogs should be closely monitored by their veterinarian with frequent recheck examinations, as relapse is common following discontinuation of medications. I personally advise recheck examinations at one, three, and six months following the conclusion of treatment.

Q. How difficult is it for a vet to diagnose blastomycosis?

A. Signs are often non-specific and exhibit similar characteristics to other common infections. Skin lesions can be mistaken for a simple skin infection, and lung changes on x-rays will often look similar to certain types of cancer. Abnormalities found in bloodwork typically show an inflammatory response within the body, which can be caused by many different disease processes. The most important information a veterinarian needs to aid in diagnosis of this disease is a detailed history, including travel and environmental exposure of the patient within the three months prior to presentation.