The Making of a New American Epidemic

Hmm, so it looks like the key parts are:

1. There's a known infectious fungus in soil, which people can inhale when dust is kicked up.

2. Some researchers believe that infecting mammals' lungs is be something it does regularly, rather than accidentally.

3. Changes in climate or land-use may mean more infectious dust. (e.g. dry reservoirs)

https://en.wikipedia.org/wiki/Coccidioidomycosis