Sorry about your friend and companion. SIL got what they thought was Valley Fever, in Az last year. Lost his job because of it. It caused what, I think they called Horners eye. The damage won't entirely go away. I don't think they have any kind of serum for it yet. Since it is in the soil and the dirt gets blown around a lot, out there, and a dog is close to the ground, not much can be done or can it? It might look unusual but perhaps there are respiratory mask for dogs.
Next time we go out there I've seriously considered wearing the mask the Japanese wear so often, when it is windy, or most of the time. Still mite not do any good.
At any rate I hope he recovers quickly but we know how the disease goes.
Bless him and you
Best Regards