Close to a dozen dogs in the Big Bay area of Michigan’s upper peninsula have been diagnosed with blastomycosis, an uncommon but regionally important disease. Blastomycosis is caused by a fungus, Blastomyces dermatitidis. It’s a dimorphic fungus, meaning it exists in 2 forms:

  • Normally, it lives in the environment in the mold form. This is the infectious form to which dogs (and people) can be exposed via inhalation, ingestion or contamination of wounds.
  • The other form is the yeast form. This develops from the mold form once it gets into the body, and this is what causes disease.

Dogs that are infected with blasto are of minimal risk to others since they are carrying the yeast form, and the yeast form is not transmissible under normal conditions. There is only a risk of infection in rare situations, such as a bite from a dog that has the yeast form in its mouth, or if someone sticks themselves with a needle that was used to sample an infected site. The main issue with finding blasto in a dog is that it is an indication that the fungus is present in the environment in the area where the dog has been in the past few months.  That means people who went to those areas may have also been exposed.

Knowing where blasto is present is important for diagnosing disease in people and animals. Blasto is also a great example of a disease when getting a travel history can be critical for diagnosis. In some regions, blasto is most common where people tend to vacation or have cottages. If a veterinarian doesn’t know that a dog has visited a high-risk area, blasto may not be considered. Not asking about travel history (or not getting a clear answer) can significantly impact the ability to diagnose this disease, and early diagnosis and treatment are critical for getting a good response.

If you live in an area where blasto is present, avoiding it can be tough. Staying away from areas that have been associated with the fungus can help, but defining this is difficult because of poor reporting and the long incubation period. Staying away from soil is pretty tough to do as a routine measure, so people living in endemic areas have to be aware of the disease and ensure that proper veterinary care is provided if there are early signs of infection (e.g. respiratory disease, skin lesion, unexplained weight loss). People who travel to areas where blasto is present should make sure their veterinarian knows about the potential for blasto exposure in any animals that may travel with them.