dunno about the Hanta virus, but Valley Fever has been around for a very, very long time. It's so endemic around where I live that around 90% of people who have lived here for more than five years have antibodies to it. When it hits hard, it hits HARD, but most of the time it 'hits' like a medium/moderate cold. And then one is immune.
I know this because I am immunosupressed, what with cancer and all, and one of the things they test you for after a bone marrow transplant (to see what vaccines you need to repeat) is Valley Fever. Yep, I'm now immune...and so is everybody in my family. Most people who get it don't even know they've had it, unless it goes to the 'second stage,' which is pretty rare.
We've known about it for a very, very long time. Yeah, coccidiomycosis....
And it's a fungus, not a virus. Just so you know.