What is Blastomycosis?

Blastomycosis is a systematic yeast-like fungal infection caused by a fungus called Blastomyces dermatitidis which lives in moist soil and in association with decomposing organic matter such as wood and leaves.

The infection typically occurs when the dog inhales the airborne fungal spores after the contaminated soil has been disturbed. This can be from an activity as benign as digging in the dirt or following a scent trail. The spores can also enter through the skin.

The fungus thrives in wet environments, such as riverbanks, lakes, and swamps, where damp soil lacking direct sunlight fosters the growth of the fungus. It is also present in areas that are rich in decaying matter, such as wooded areas, forests, and farms. It is a naturally occurring North American fungus, with the highest prevalence of infection taking place in geographic areas located near water – such as the Mississippi, Ohio, Missouri, and Tennessee River basins. It has also been found in the area of the Great lakes and St. Lawrence River, Southern Canada, and outside the endemic area in Colorado.

What is happening?

• A small spore (conidia) is shed from the mycelial phase of the organism growing in the soil and inhaled, entering the terminal airway.
• At normal body temperature, the spore becomes yeast, which initiates the infection in the lungs and spreads systemically. Although infection almost always begins in the lungs before being disseminated through hematogenous or lymphatic routes to other body tissues, lung lesions occasionally resolve by the time infection in other sites becomes apparent.
• From this focus of mycotic pneumonia, the yeast disseminates hematogenously throughout the body.
• The immune response to the invading organism produces a pyogranulomatous infiltrate to control the organism.
• The result is organ dysfunction.
• The severity of lung involvement and invasion into the brain affect the prognosis.
• Early diagnosis improves the chance of survival, as 25% of dogs die during the first week of treatment.

Humans can get Blastomycosis as well

Blastomycosis does not spread from animals to people, except through bite wounds. Since it is acquired from an environmental source pet owners should be aware that they might have been exposed at the same time their pet did. If these pet owners have respiratory issues or skin lesions they should inform their physicians that they might have been exposed. In humans lung infection can occur after a person inhales the airborne, microscopic fungal spores from the environment; however, many people who inhale the spores do not get sick. Only about half of the people who are infected with blastomycosis will show symptoms. If symptoms occur, they usually appear between 3 and 15 weeks after being exposed to the fungus. The symptoms of blastomycosis are similar to flu symptoms and include fever, chills, cough, muscle aches, joint pain, and chest pain. In very serious cases of blastomycosis, the fungus can disseminate (spread) to other parts of the body, such as the skin and bones.

Sources

1. http://veterinarymedicine.dvm360.com/canine-blastomycosis-review-and-update-diagnosis-and-treatment
2. http://www.petmd.com/dog/conditions/respiratory/c_multi_blastomycosis
3. http://www.cdc.gov/fungal/diseases/blastomycosis/
4. http://commons.wikimedia.org/wiki/File:Blastomycosis_cropped.JPG
5. Tilley, L., & Smith, Jr., F. (2011). Blastomycosis. In Blackwell’s five-minute veterinary consult: Canine and Feline (Fifth ed., pp. 174-175). Ames, IA: Wiley-Blackwell.
6. Photo of Dubuque Iowa Julien Dubuque Bridge: CC BY 2.0 Dirk – originally posted to Flickr as Dubuque Iowa Julien Dubuque Bridge