If you suspect that someone you love may be suffering from prion disease, ask your doctor about a nasal swab RT-QuIC test. RT-QuIC is typically done via a painful and dangerous lumbar puncture: however, it can also be done safely and effectively with just a nasal swab. The test has a 0% false positive rate, and anywhere between 3-20% false negative rate.
EDIT: This test does not appear to be very accessible, after all. All CJD tests are managed by the CDC, and they have made it almost impossible to get this test. They prefer people be subjected to a painful spinal draw, instead. We have been communicating with a pharma company to see about developing this test and making it more widely available, but that effort has stalled til we can find the time to write a patent for it.