Apparently the only options for diagnostic testing are brain biopsy and pulling CSF samples, both of which are probably a non-starter for screening purposes across a population.
Clinical Laboratory Tests Used To Aid in Diagnosis of Human Prion Disease Allyson Connor, Han Wang, Brian S. Appleby, Daniel D. Rhoads Journal of Clinical Microbiology Sep 2019, 57 (10) e00769-19; DOI: 10.1128/JCM.00769-19