I read that it may have a longer asymptomatic period than mad cow does in humans.
Yes. Remember that dementia can also be caused by prion disease as well.
As for testing the University of Minnesota developed an accurate test that’s conducted in a lab. Check with your local state/province for more info, ie: Manitoba currently has online instructions on how to harvest lymph nodes for testing.
edit to add … the Minnesota test uses venison/elk muscle tissue so doesn’t take weeks to get results (like testing lymph nodes does).