Overview

Alzheimer’s disease mostly affects the elderly. While some of its symptoms can be managed with drugs, a cure is yet to exist. This is primarily because we still don’t know what causes it. However, a new study suggests two very common viruses most people carry could trigger the onset of Alzheimer’s.

The science and other stuff to know

It’s estimated that one in two Americans have been infected with the herpes virus which can cause cold sores. Some people develop painful blisters, while others have no symptoms. Eventually, the virus becomes dormant, still residing in your body but inactive.

Now, a team of researchers at Tufts University and the University of Oxford has demonstrated that Varicella Zoster Virus (VZV), which commonly causes chickenpox and shingles, may help re-awaken the Herpes Simplex (HSV-1). As per the study, which was published in the Journal of Alzheimer’s Disease, the herpes virus lies dormant within the neurons of the brain. But when activated, it leads to the accumulation of tau and amyloid beta proteins and loss of neuronal function. These are signature features common with Alzheimer’s patients.

“Our results suggest one pathway to Alzheimer’s disease, caused by a VZV infection which creates inflammatory triggers that awaken HSV in the brain,” said Dana Cairns, GBS12, a research associate in the Biomedical Engineering Department. “While we demonstrated a link between VZV and HSV-1 activation, it’s possible that other inflammatory events in the brain could also awaken HSV-1 and lead to Alzheimer’s disease.”

So what?

The new study provides evidence of an indirect role for VZV in Alzheimer’s, through the reactivation of HSV-1 in neurons. “We have been working off a lot of established evidence that HSV has been linked to increased risk of Alzheimer’s disease in patients,” said David Kaplan, Stern Family Professor of Engineering and chair of the Department of Biomedical Engineering at Tufts’ School of Engineering.

“We know there is a correlation between HSV-1 and Alzheimer’s disease, and some suggested the involvement of VZV. But what we didn’t know is the sequence of events that the viruses create to set the disease in motion,” Kaplan added. “We think we now have evidence of those events.”

Exploring methods to halt the activation of VZV and the potential reactivation of HSV-1 could be a therapeutic approach for Alzheimer’s. According to the study, vaccination is the best approach to go about it. Previous research has linked VZV to Alzheimer’s disease, and furthermore, vaccination against shingles caused by VZV can reduce the risk of Alzheimer’s and dementia.

What next?

Despite the “ambitious” claims that VZV and HSV-1 could trigger the onset of Alzheimer’s, some researchers remain skeptical. “Researchers have suggested for many years that [herpes viruses may cause Alzheimer’s disease] and it is fair to say that most workers in the field have remained skeptical about these claims,” says Rob Howard, a professor of Old Age Psychiatry, UCL. “There is nothing in these new data that will dispel this skepticism.”