Can herpes virus cause Alzheimer's disease?

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New evidence suggests a common virus may play a role in who develops Alzheimer's disease. 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. Previously, experts have also found antibodies against HSV-1 - form of herpes, which causes sores in the blood in people with Alzheimer's disease.

In a study published on June 21 in the journal Neuron, researchers say they've found strong evidence to suggest that two strains of the human herpes virus - 6A and 7 - may contribute to the disease that robs people of their memory and cognitive functions.

"Previous studies of viruses and Alzheimer's have always been very indirect". "It therefore doesn't change what we already know about the causes of dementia, doesn't mean that having cold sores put you at increased risk of getting it and people shouldn't be unduly anxious".

"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. Presence of these antibodies indicated the encounters of the person with this virus sometime during their lives. Alzheimer's is characterised by building up of amyloid sticky plaques in the brain.

When the investigators compared large viral RNA and DNA datasets with networks of human genes associated with Alzheimer's, they saw what may be the first hints of a viral mechanism that could trigger or worsen the disease. They tested the brain samples from the Mount Sinai Brain Bank, he said and were so surprised at the finding that they tested additional samples from other brain banks and found same results.

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"This study represents a significant advancement in our understanding of the plausibility of the pathogen hypothesis of Alzheimer's", said the study's senior author, Joel Dudley, PhD, director of the Institute for Next Generation Healthcare at the Icahn School of Medicine at Mount Sinai. Gandy said that the Alzheimer's genes were apparently being "modulated" by the HHV6/7 and so it could be the viral proteins that could be turning on the genes responsible for Alzheimer's disease.

Tanzi explains that having a herpes virus "does not mean you're going to get Alzheimer's".

The viruses highlighted are not the same as those that cause cold sores, but much more common forms of herpes that almost everyone carries and which don't typically cause any problems.

"I don't think we can answer whether herpes viruses are a primary cause of Alzheimer's disease".

"While these findings do potentially open the door for new treatment options to explore in a disease where we've had hundreds of failed trials, they don't change anything that we know about the risk and susceptibility of Alzheimer's disease or our ability to treat it today", Gandy said.

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