All the best to your brother.
About 1980, after a round of guesses, from some Drs. I was found to have been exposed to histo.
Unfortunately for me it was only after one of my lungs was opened up and they could test the spot that was showing up on X rays and different scans.
After the fact I found out there is a tine test they could have performed on me that would have told them if I had ever been exposed to histo.
In my case the lung had encapsulated the fungus with calcium and the histo had not hurt me, but I almost died from complications of the operation.
I was told that you don't have to be exposed to birds or whatever but that in the Mississippi and Ohio river valleys the spores are in the air all the time.