"I don't think we can answer whether herpesviruses are a primary cause of Alzheimer's disease", says Dudley.
American researchers found that two strains of human herpesvirus were found in the brains of people with Alzheimer's disease at levels up to twice as high as in those without Alzheimer's.
Reporting in the June 21 issue of the journal Neuron, the authors emphasize that their findings do not prove that the viruses cause the onset or progression of Alzheimer's.
Thursday's study has even some specialists who never embraced the infection connection saying it's time for a closer look, especially as attempts to block those so-called beta-amyloid plaques have failed.
"The research is not a proof of HHV involvement in Alzheimer's", he said.
A robust and sophisticated new study has now exploded onto the scene, rekindling the viral hypothesis for Alzheimer's through an accidental discovery.
However, he said their high concentration in the healthy human brain also suggests a role for these nutrients in cognition.
The team from Mount Sinai and Arizona State University came up with some viral suspects - by accident.
These results could provide a new avenue of research aimed at preventing and treating Alzheimer's, said Keith Fargo, director of scientific programs and outreach for the Alzheimer's Association.
Using computational tools to analyze these large datasets, the researchers were able to generate a picture of the genetic, transcriptional, and molecular networks that underpin AD development and progression and how viruses are potentially involved.
"It's conceivable there are ways in which viruses interact that we haven't really taken very seriously before, in terms of provoking the pathology or the expression of disease", senior author Sam Gandy, MD, PhD, told MedPage Today.
The findings were based on RNA sequencing on four brain regions in more than 600 samples of postmortem tissue from people with and without Alzheimer's. They found that viral genes were influencing other known Alzheimer's genes and molecules-evidence that the viruses are directing at least part of the disease process. But it was never clear if germs were merely bystanders, or actively spurring Alzheimer's.
They found that Alzheimer's biology is likely impacted by a complex group of viral and host genetic factors. "This analysis allowed us to identify how the viruses are directly interacting with or coregulating known Alzheimer's genes", said Dudley.
"However many scientists, including myself, have been concerned by the failures of recent large trials of drugs that have been developed to remove amyloid from the brain, and we have therefore focused on alternative thinking". Ruth Itzhaki, a neurobiologist at the University of Manchester in the United Kingdom, who has led numerous studies linking HSV-1 with Alzheimer's, says she has suffered "derision and vituperative hostility" for pursuing this line of inquiry.
"This study illustrates the promise of leveraging human brain samples, emerging big data analysis methods, converging findings from experimental models, and intensely collaborative approaches in the scientific understanding of Alzheimer's disease and the discovery of new treatments", said study co-author Eric Reiman, executive director of the Banner Alzheimer's Institute and university professor of neuroscience at ASU. Already, NIH is funding a first-step study to see if an antiviral drug benefits people who have both mild Alzheimer's and different herpes viruses. It may not even have penetrated the brain.
The finding adds credence to a decades-old idea that an infection can cause Alzheimer's disease. "The brain was always thought to be a sterile place. We still have to work out the microbe side of the story", said Tanzi, who is looking for bacteria and other bugs in what's called the Brain Microbiome Project. "It's absolutely not true".