Until recently, it was not thought that human CJD could be diagnosed before death. Tonsil biopsy samples have recently been used in investigation. And there have been claims for a test using cerebrospinal fluid that not only diagnoses CJD but also distinguishes it from Alzheimers, which has similar symptoms. However, validating such tests requires carrying it out in a substantial number of clinically suspected CJD cases and comparing the results with those of subsequent postmortem histopathological examination of brains, and finding a very high degree of correlation. Probably the best explanation of prions for laypersons appeared in the January 1995 issue of Scientific American in an article written by Stanley B. Prusiner, the leading proponent of, and winner of a Nobel Prize in 1997 for, the prion hypothesis.
Different species have brain cell proteins of different compositions.
For example, the human prion differs by 30 different amino acids from the cattle prion. Protein molecules have three-dimensional folded shapes. The distorted shape is protease-resistant, i.e. it is not broken down into amino acids in the digestive system. It is also highly resistant to normal heating and to normal sterilants. Another, but only two-dimensional, example is the dressmaker's paper patterns that enable the cloth to be cut to their exact sizes and shapes.