What does your vet recommend?

Hmmm. A search via google.com turns up some interesting info, esepcially when you use the name of the causal fungus -- Blastomyces dermatitidis.

Tom Volk's Mushroom Pages has a thorough discussion with some very clinical pictures -- all in all, stuff that folks with queasy stomachs should avoid.

In part that page said:
"Interestingly, there is no evidence of human to human or animal to human transmission of the disease. Why do you think this is the case? The answer is at the end of this page*.
Animal blastomycosis is most common among dogs, especially the hunting breeds."

Another web page notes that it's a very rare infection.

Your best source of info is local as your vet and medical community will know how common the infection is, or is not, in your region. Another possibility if you travel with your dog, or if it was a hunting dog, is that the dog was infected elsewhere.

You said "it's believed".

Is it a proven fact?

The reason I ask, is because we have parrots and read messages about parrots. Occassionally, some vets misdiagnose certain problems if it's outside their specialty.

If it's an indiputable fact, that's different. If it's an opinion or "believed" situation, consider a second opinion by a vet that specializes in a certain breed, or animal, like canines.

Spores are in the air by the billions. If your yard has them, it's possible that other property around has them.

In other words, if pine pollen was deadly to me, it would do little good to cut down my pine tree, if half my neighbors had pine trees.

Just a few ideas.

Hope you find the right path.