When most pet owners think "infection," bacteria and viruses come to mind. But fungi are also sometimes to blame. I’m not talking mushrooms here, but microscopic fungal organisms that can invade the body and cause disease.
Some fungal infections (e.g., ringworm or yeast infections of the skin and ears) are common, and while they can certainly be detrimental to an individual’s quality of life and expensive to treat, they are not generally life threatening. Other fungal diseases are much more serious. One of these is blastomycosis — or blasto, as it is often called.
Blasto most commonly infects dogs, although other species, including cats and people, can be affected (but not through contact with infected dogs). The organism lives in moist, sandy, acidic soil that is rich in organic matter, which explains why the only case I’ve diagnosed since moving to the arid west was in a dog that lived part time near Lake Michigan. Blasto "hotspots" include Mississippi, Ohio, Missouri, Tennessee, the St. Lawrence River valley, the mid Atlantic states, and areas around the Great Lakes.
Dogs usually inhale Blastomyces spores from the soil, leading to infection of the lungs. Once established there, the organisms can travel anywhere in the body. Symptoms depend on where the infection localizes but some combination of poor appetite, weight loss, coughing, difficulty breathing, limping, eye problems, skin lesions (particularly around the toenails), enlarged lymph nodes and fever are common. If the organism infects the brain, seizures and other neurologic problems may also develop.
Diagnosing blastomycosis usually involves first eliminating other more common diseases through blood chemistry panels, complete blood cell counts, a urinalysis and X-rays, and a rising index of suspicion based on those results.
For example, blasto-related pneumonia will often have a "snow storm" appearance on chest X-rays, which differs from the typical look of a bacterial or viral pneumonia. Serologic testing can help determine whether or not a dog has been exposed to blasto, but the results can be hard to interpret since early infections may be missed and positive results aren’t always associated with a current, active infection. Ideally, the diagnosis should be based on finding the organism on tissue or cytological samples taken by needle aspirate, smear, or biopsy.
When caught early enough in the course of the disease, blasto can often be effectively treated with anti-fungal medications, and symptomatic and supportive care. Itraconazole is the drug of choice, although other medications like fluconazole or amphotericin might be appropriate under certain circumstances. Blasto of the eye is especially difficult to eradicate because of the limited ability of anti-fungal medications to pass from the bloodstream into ocular structures
Treating fungal infections takes patience. Dogs with blasto may not begin to improve for a week or two after appropriate treatment has begun. Drug therapy often needs to be continued for many months to avoid relapses once treatment is stopped.
Veterinarians in blasto-endemic areas should be familiar with the disease and have it towards the top of their rule-out lists for dogs with characteristic symptoms. If, however, you have recently moved from or traveled to one of these areas and your dog gets sick, be sure to tell your vet. This information is critical if your dog is to benefit from a prompt and accurate diagnosis and avoid potentially life threatening delays in treatment.
Dr. Jennifer Coates
Image: Charlie’s X-ray (to see the "snow storm" appearance in the full X-ray image, click here), shared by Charlie’s owner, Bob, on blastomycosis.ca