There is substantial evidence that Alzheimer's is related to an increased likelihood of infective agents appearing in the brain. Some researchers believe that infective agents are the principle cause of Alzheimer's. There are a number of bacteria that reside in the human digestive system and can co-exist with our own cells without any harm. However, H. pylori, one that is quite common, has been recently shown to be responsible for stomach ulcers. It has been suspected that H. Pylori might be implicated in Alzheimer's, and, indeed, a recent study showed that Alzheimer's patients had a significantly higher concentration of an antibody against H. Pylori in both their cerebrospinal fluid and their blood than non-Alzheimer's controls . H. pylori was detected in 88% of the Alzheimer's patients but only 47% of the controls. In an effort to treat the Alzheimer's patients, the researchers administered a potent combination of antibiotics, and assessed the degree of mental decline over the next two years . For 85% of the patients, the infection was successfully routed, and for those patients, cognitive improvement was also detected after two years had elapsed. So this was a nice example of the possibility of treating Alzheimer's through antibiotics.
C. pneumoniae is a very common bacterium, estimated to infect 40-70% of adults. But there's a big difference between a bacterium being in the blood stream and making its way into the inner sanctum of the brain. A study of post-mortem samples from various regions of the brains of Alzheimer's patients and non-Alzheimer's controls revealed a remarkably different statistic: 17 out of 19 Alzheimer's brains tested positive for the bacterium, whereas only 1 out of 19 brains from the control group tested positive .
Many other infective agents, both viruses and bacteria, have been found to be associated with Alzheimer's, including herpes simplex virus, picornavirus, Borna disease virus, and spirochete . One proposal was that a particular bacteriophage -- a virus that infects the bacterium C. pneumoniae -- might be responsible for Alzheimer's . The authors argued that the phages might make their way into the mitochondria of the host cell and subsequently initiate Alzheimer's.