So, here's a frightening thought; you go in for surgery and the surgeon uses instruments on you which had previously been used on an Alzheimer's patient. The hospital had sterilized the instruments. They were not negligent. You later develop Alzheimer's. Coincidence?
There's a new theory that there could be a form of Alzheimer's which is transmitted from person to person in the manner described above.. This theory is a new one and a highly controversial one. If true, it would introduce a third type of Alzheimer's. We know there is spontaneous Alzheimer's (it happens and we don't know why) and familial Alzheimer's (it is a result of an inherited gene). If there is a Transmittable form of Alzheimer's, it would mean that this form of the disease is not the result of a gene but the result of prions.
As I stated, the theory is controversial and government health agencies are coming out to indicate there is no such thing as transmittable Alzheimer's. The finding is from one study which only looked at 8 brains. Much more work and a greater sample set is needed before any of us should worry.