Are Infections the cause of Alzheimer's?

Interesting new science has been published by a team of researchers at Harvard. Published last month in the journal Science Translational Medicine is a study that tested whether infections, including mild infections, may provoke reactions in the brain that protect from infection but lead to Alzheimer's disease later on in life. 

The researchers propose the following scenario. An intruder to the brain like a virus, bacterium, or fungus bypasses the normal barrier to entry to the brain. The barrier, also known as the blood brain barrier, becomes leakier as we age which allows this scenario to happen more  often. In response to the intruders the brain reacts by producing a set of proteins call beta amyloid to cage them in. This leads to plaques in the brain which are markers of Alzheimer's disease.

So far researchers have infected brains cells in petri dishes and found beta amyloid produced in response. The findings have been reproduced in yeast, roundworms, fruit flies, and mice. According to the study author "each plaque had a single bacterium at its center."  Mice that didn't react to infection by producing plaques were at greater risk for dying from infection. 

It is worth noting that the research regarding the connection between infection and Alzheimer's disease is preliminary and needs further study. As with everything in medicine it could be years before we get more definitive answers.