Blastomycosis
My very best quail dog suddenly became labored in her breathing not long after the close of a great upland bird season. After examining her and osculating her chest, I had determined that the appropriate course of action was to get a chest radiograph (x-ray) and a diagnostic lab work up. The radiograph demonstrated a classic pattern within the lung tissue of an infiltrative type disease such as cancer or mycotic (fungal which includes Blastomycosis, Histoplasmosis, and Coccidioidomycosis) disease. I had hunted her in the Southwestern desert on quail and was concerned about Valley Fever which is a fungal disease known as Coccidioidomycosis. Serological blood tests for all the mycotic diseases were negative. She ended up having an incurable type of cancer of the endothelium of the blood vessels called Hemangiosarcoma. Jibber’s clinical signs and chest radiographs were very similar to those of a bird dog with Blastomycosis.
Blastomycosis is a systemic fungal (mycotic) infection caused by a soil borne organism called Blastomyces dermatitidis. The small mold (fungal) spores are inhaled from moist soil, and enter into the dog’s respiratory tract and drift their way to the terminal airways in the lungs. Once these spores reach body temperature in the host (dog, cat, human), they transform into a yeast which is the active or infectious form of the organism. When the organism has successfully converted into the yeast form within the lungs it causes a pyogranulomatous pneumonia. The yeast can then circulate via the blood stream throughout the body.
The organs/systems that are most commonly affected (> 85% in the dog) is the respiratory system causing severe lung disease. The lungs
are not the only system that can be affected as the yeast can disseminate via the blood vessels to other distant organs which can include bones, eyes, skin, lymph nodes, brain, testes, prostate, mammary glands, nasal cavity, gums and vulva (less common) to name a few. The yeast causes the body to produce a severe inflammatory process within the infected organs to try and contain the organism or to wall it off—which ultimately causes harm in the dog’s body.
All dogs and people are susceptible to infection, but there seems to be a higher incidence in field trial, sporting or hunting breeds—this increased
incidence has to do with these athletic animals being at an increased risk of exposure because of their job. Blastomyces strongly depends on the proper environmental conditions in order for it to grow and prosper. These environmental conditions occur in the exact areas that we upland bird aficionados take our bird dogs like the Great Lake States, the St. Lawrence River, Missouri, Ohio, and Mississippi River valleys, the Tennessee River basins and certain areas on the eastern seaboard and a few Canadian providences. Wet environs foster growth of the mold such as swamps, stream, and river and lake beds. The time from exposure to the spores until the dog has clinical disease is typically 5 to 12 weeks.
Dogs that are infected with Blastomyces can have a wide range of clinical signs that are usually associated with the organ/system that is infected or involved. Historical findings may include such vague signs as weight loss, fever, anorexia, respiratory distress or coughing, eye inflammation, severe lameness, and draining skin wounds. These dogs can have elevated body temperature as high as 104 degrees F (40 degrees C) (the normal canine body temp is 100.0 to
102.6 degrees F). Other clinical findings your veterinarian my ascertain are harsh, dry lung sounds, conjunctivitis with ocular exudates or even secondary glaucoma, enlarged peripheral lymph nodes, testicular swelling and prostate enlargement.
Blastomycosis infections can imitate many other diseases that dogs can acquire—this makes the diagnosis difficult in many cases. The lesions that
Blastomyces can create within the bird dogs’ body can resemble diseases such as heartworm disease, bacterial pneumonia, heart failure, and lung and bone cancer, cancer of the lymphatic system like lymphoma, tick borne diseases, and a myriad of others. Laboratory results are often
normal or inconclusive. Occasionally yeast spores can be seen under the microscope from skin wounds or urine samples in dogs with prostate infections. Diagnosis is generally based on the radiographs of the dog’s chest, geographical location of the dog, and gut intuition.
Radiographs of a dog with clinical Blastomycosis can resemble those of a dog with lung or bone cancer—again this makes the diagnosis complicated. The
changes seen on the film in the lungs are inconsistent with bacterial pneumonia and often times the lymph nodes in the chest or also enlarged. The changes in the lungs are classic for lung mycotic infections or cancer. The next step your veterinarian will take to make a definitive diagnosis is to run a serological or blood test called an AGID which tests for antibody titers to the organism (Blastomyces). A positive test result strongly supports the diagnosis; however, a negative test can be common in dogs that are in the very early stages of the disease process. Looking at cytology (tissue samples under the microscope) samples from infected lymph nodes, lung aspirates, or draining skin wounds may also reveal budding yeast spores and further confirm the diagnosis.
The reference lab that we currently use in our office states this about their serological test for Blastomycosis. “A positive serological result is consistent with, but not diagnostic for Blastomycosis. A definitive diagnosis of Blastomycosis is based on the demonstration of the organism in cytological or histopathological specimens. A combination of supportive history and clinical signs, suggestive radiographic findings plus positive serology may be substituted for organism identification. A negative result does not rule out active Blastomycosis.”
Once a definitive diagnosis of Blastomycosis has been confirmed, treatment is immediately initiated. Treatment is extremely costly and requires a minimum of 60 to 90 days. Many bird dogs are humanely euthanized due to the enormous expenses of therapy. The mainstay of therapy is antifungal drugs such
as Ketoconazole or Itraconazole given orally twice daily. Itraconazole is the current drug of choice for Blastomycosis and is given orally
every 12 hours with a high fat diet to get the dog’s therapeutic blood levels swiftly up. Itraconazole can lead to anorexia and an elevation in a dog’s liver specific enzymes, and it (very rarely) can lead to ulcerative skin disease.
The expected outcome of dogs properly diagnosed and rapidly treated for Blastomycosis is favorable. Prolonged diagnoses can significantly decrease their chances of survival. Death occurs in 25% of infected dogs in the very first week of therapy. The disease has a history of recurrence in about 20% of dogs within 3 to 6 months of their treatment termination. Treatment is continued for 60 days and follow up radiographs are taken of the lungs to see if they
have a normal appearance. If the lung radiographs are normal at the 60 days mark, then treatment is continued for 30 more days and then stopped. Radiographs are repeated again in 30 days and again at 120 days after the treatment have been terminated to insure that there is no further evidence of disease.
People can not get Blastomycosis from their dog except through a bite wound. People can, however, contract the disease in the same manner as their bird dog acquired it—from the environmental source. It’s important to note that dogs are 10 times more likely to acquire Blastomycosis than their human counter-parts.
Lesions in the lungs that look exactly like Blastomycosis.
