It probably has already infected a small number of people for decades. Chalked up to dementia, seizures, whatever. If it's not on the radar for doctors…it's probably not reported or investigated. Speaking from experience, we don't always have a clear answer of why someone dies in the medical field. Not to mention all of the tiny hospitals out there with limited resources and specialists.
It makes me think twice about not testing my deer…but I'm definitely more likely to die driving on the way to hunt than from eating an infected deer.