The most frequent misdiagnosis of CJD among the elderly is Alzheimer's disease.[55] Neither CJD nor Alzheimer's can be conclusively diagnosed without a brain biopsy,[56] and the symptoms and pathology of both diseases overlap. There can be spongy changes in Alzheimer's, for example, and senile Alzheimer's plaques in CJD.[57] Stanley Prusiner, the scientist who won the Nobel Prize for his discovery of prions, speculates that Alzheimer's may even turn out to be a prion disease as well.[58] In younger victims, CJD is more often misdiagnosed as multiple sclerosis or as a severe viral infection.[59]

Over the last 20 years the rates of Alzheimer's disease in the United States have skyrocketed.[60] According to the CDC, Alzheimer's Disease is now the eighth leading cause of death in the United States,[61] afflicting an estimated 4 million Americans.[62] Twenty percent or more of people clinically diagnosed with Alzheimer's disease, though, are found at autopsy not to have had Alzheimer's at all.[63] A number of autopsy studies have shown that a few percent of Alzheimer's deaths may in fact be CJD. Given the new research showing that infected beef may be responsible for some sporadic CJD, thousands of Americans may already be dying because of Mad Cow disease every year.[64]

Nobel Laureate Gajdusek, for example, estimates that 1% of people showing up in Alzheimer clinics actually have CJD.[65] At Yale, out of a series of 46 patients clinically diagnosed with Alzheimer's, six were proven to have CJD at autopsy.[66] In another study of brain biopsies, out of a dozen patients diagnosed with Alzheimer's according to established criteria, three of them were actually dying from CJD.[67] An informal survey of neuropathologists registered a suspicion that CJD accounts for 2-12% of all dementias in general.[68] Two autopsy studies showed a CJD rate among dementia deaths of about 3%.[69,70] A third study, at the University of Pennsylvania, showed that 5% of patients diagnosed with dementia had CJD.[71] Although only a few hundred cases of sporadic CJD are officially reported in the U.S. annually,[72] hundreds of thousands of Americans die with dementia every year.[73] Thousands of these deaths may actually be from CJD caused by eating infected me