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Education: GRSRS&EC Article Library

No Longer Rare:  by Jennifer S. Wilcox, Published in GREEAT Times


  Blastomycosis (Blasto) in the dog is a commonly misdiagnosed systemic fungal disease of dogs, humans and other mammals. It is a great pretender and opportunist that can be mistaken for cancer, viral infections, Lyme Disease, or other systemic fungal diseases such as Valley Fever. Many dogs die or are euthanized each year due to delay in treatment as the result of a missed or erroneous diagnosis. Involvement of the eye may cause loss of vision or necessitate the removal of the eye.  Relapse is also a concern, more often reported in females.  


  Canine Blastomycosis is caused by Blastomyces dermatitidis. This parasitic fungus grows as a mold in moist soil or decaying vegetation and releases spores into the environment that can be inhaled by animals or humans. Young dogs that have access to the outdoors are prime candidates for blastomycosis infection, but infection has been documented in all canine breeds, cats, horses and ferrets.


  Normally, blastomycosis infection will begin in the lungs after spores are inhaled and transform into large thick-walled budding yeast, which can multiply and disseminate to other areas of the body.  Dissemination into organs, lymph nodes, eyes, testicles, joints, skin, as well as the central nervous system, is a grave risk.


  A diagnosis of Canine Blastomycosis must be made promptly in order to begin treatment with antifungal medications. Unless Blasto is suspected, valuable time is often wasted testing and treating for viral and bacterial infections while the fungus disseminates. Without quick recognition, accurate diagnosis, and access to reasonably priced medications, many animals are unnecessarily lost to Blasto. A high index of suspicion is crucial.


  Blastomycosis cannot be eradicated from the environment, however, one may attempt to avoid or remove possible sources of contamination, such as mulched areas of flower beds, paths, bedding, areas of wetlands, etc.  The idea of a commercial fungicide has been discussed, but there are none currently available that are effective against Blasto.


 With the advent of compounding pharmacies and generic antifungal medications, treatment is now more effective and affordable, making successful outcome for these animals more attainable than ever. Sadly enough, as the symptoms can be widely varied and non-specific, there is sometimes a reluctance to diagnose what has previously been considered a “rare” condition.


Risk Factors:


• Endemic Areas, US - Mississippi, Missouri, Ohio River valleys, Eastern Seaboard, areas adjacent to the Great Lakes.  States with highest endemnicity are Wisconsin, Minnesota, Missouri, Illinois, Michigan, Kentucky, West Virginia, Arkansas, Tennessee, North Carolina, South Carolina, Louisiana, and Mississippi. Other endemic states include Indiana, Iowa, Ohio, Virginia, Georgia, and Alabama. However, cases do occur outside the endemic areas.  


• Endemic Areas, Canada - Blasto is prevalent in Kenora, Ontario. Also found in Manitoba, Ontario (Kenora, Sault Ste. Marie, Chapleau), Quebec, New Brunswick, in particular areas around the Great Lakes and in a small area a small area in New York and Canada along the St. Lawrence River. Has also been increasingly reported along the Georgian Bay coastline (including Midland and Penetang), Dryden, and in Southern Ontario at the Rockwood Conservation area.


• Environment  - Research shows that exposure to wet or decaying organic material, recently disturbed soil, rotting vegetation, bird droppings, and landscaping projects is a strong indicator of disease possibility. Some research has shown a strong link to wood mulch and importation of non-local soil.  Patient history will often reveal exposure to mulched areas and disturbed soil in parks, yards, walking paths, etc. By questioning an owner about the animals’ activities, it is often found that exposure may have occurred while vacationing, camping, or visiting an area where Blastomycosis is endemic.


• Breed/Age – Young, large-breed dogs  with the highest rates of infection are normally Coonhounds,

Pointers, and Weimaraners.  This is normally attributed to higher exposure to endemic areas due to use in hunting.  Breed, size, and age, however, are not a reliable indicator of susceptibility, as all are at risk




  After initial spore inhalation, incubation can range from days to weeks, sometimes months, which makes pinpointing a source of infection extremely difficult.  The presentation of Blasto is often non-specific, and can imitate a range of other diseases.  Symptoms include:


• Lethargy

• Persistent fever of 103 degrees or more

• Anorexia

• Vomiting

• Persistent, usually non-productive cough

• Exercise intolerance

• Respiratory symptoms, fungal pneumonia

• Ocular infection, sudden blindness

• Depression

• CNS symptoms: twitches, stumbling gait, loss of coordination

• Skin ulcerations, non-healing lesions

• Lumps, nodes, swellings

• Weight loss

• Hair loss

• Lameness, fungal arthritis

• Hematuria





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