The remote idea that microbes trigger Alzheimer’s Disease (AD) is now gaining traction among the scientific community and could explain the origins of amyloid-b-plaque, that infest the brains of people with Alzheimer’s. AD researchers now believe that infections, including ones that are too mild to elicit any symptoms, trigger a fierce body/brain reaction that leaves debris in the brain, causing AD. According to work from several independent groups, any virus, fungus or bacterium gets into the brain passing through the blood-brain barrier—that is compromised as people age. The brain’s defense system tries to fight off the invader by encapsulating them in a cage of proteins, called beta amyloid. The microbe gets trapped in the cage and dies. What is left behind is the remnants of the battle—a plaque that is the hallmark of Alzheimer’s.
In one study, a group of researchers injected Salmonella bacteria into the brains of young mice that did not have plaques. The bacteria attracted plaque formation and the hippocampus was full of plaques with the bacterium trapped in its core. Other investigators reported that people who had developed Alzheimer’s had higher levels of antibodies to herpes, an indicator of a previous infection, than people who did not have the disease providing a plausible explanation for plaque formation. The idea that Alzheimer’s might be linked to infection isn’t limited to any one pathogen; the hypothesis is simply that, following infection, certain pathogens gain access to brain, and the brain’s defense system mounts an immune response resulting in the accumulation of amyloid-β and plaque formation.