In their detailed analysis, researchers examined the postmortem brains of 622 people with Alzheimer's disease, and 322 brains of people without it, and found two herpes viruses that were abundant in the Alzheimer's brains.
The results, based on tests of brain tissue from almost 1,000 people, found that two strains of herpes virus were far more abundant in the brains of those with early-stage Alzheimer's than in healthy controls. After an 18-month study examining the effects of nutritional compounds found in foods such as trout, broccoli and peppers on people with Alzheimers, the team from the Nutrition Research Centre Ireland (NRCI) claims to have done a statistically significant finding. Readhead said the connection between finding the virus in the blood and it activating the Alzheimer's genes and triggering the disease is still not understood well.
"We mapped out the social network, if you will, of which genes the viruses are friends with and who they're talking to inside the brain", Dudley told NPR, offering an analogy: "If the viruses are tweeting, who's tweeting back?"
The team found viral genetic material at far higher levels in Alzheimer's-affected brains than in normal ones.
Dudley said this kind of research has always been controversial in the community.
Whatever the case, the new studies make the once-controversial idea that a virus is involved in Alzheimer's another reasonable avenue of study. He also hopes it could be the beginning of research that would provide new targets in the brain for drugs to treat the condition.
"However, if viruses or other infections are confirmed to have roles in Alzheimer's, it may enable researchers to find new antiviral or immune therapies to treat or prevent the disease", Fargo said.
The scientists caution that people shouldn't be alarmed by their discovery, because this particular set of herpes viruses is common.
"This is the most compelling evidence ever presented that points to a viral contribution to the cause or progression of Alzheimer's", said study co-author Dr. Sam Gandy, a professor of neurology and psychiatry and director of the Center for Cognitive Health at Mount Sinai in NY.
"We didn't go looking for viruses, but viruses sort of screamed out at us", said Ben Readhead, assistant professor at Arizona State University-Banner Neurodegenerative Disease Research Center and lead author.
But in another study soon to be published, Tanzi showed biologically how both HHV6 and a cold sore-causing herpes virus can trigger or "seed" amyloid plaque formation, supporting the Mount Sinai findings.
The study also suggested that the presence of the herpes viruses in the brain could influence or control the activity of various genes linked to an increased risk of Alzheimer's. "Our work identified specific biological networks that offer new testable hypotheses regarding the role of microbial defense and innate immune function in the pathophysiology of Alzheimer's".
Written by Jen Christensen for CNN.