Alzheimer’s disease can begin almost imperceptibly, often masquerading in the early months or years as forgetfulness that is common in older age. What causes the disease remains largely a mystery.
But researchers at Tufts University and the University of Oxford, using a three-dimensional human tissue culture model mimicking the brain, have shown that varicella zoster virus (VZV), which commonly causes chickenpox and shingles, may activate herpes simplex (HSV), another common virus, to set in motion the early stages of Alzheimer’s disease. Normally HSV-1 – one of the main variants of the virus – lies dormant within the neurons of the brain, but when it is activated it leads to accumulation of tau and amyloid beta proteins, and loss of neuronal function-;signature features found in patients with Alzheimer’s. 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. One of the first to hypothesize a connection between herpes virus and Alzheimer’s disease is Ruth Itzhaki of the University of Oxford, who collaborated with the Kaplan lab on this study.
“We know there is a correlation between HSV-1 and Alzheimer’s disease, and some suggested involvement of VZV, but what we didn’t know is the sequence of events that the viruses create to set the disease in motion,” he said. “We think we now have evidence of those events.” According to the World Health Organization, an estimated 3.7 billion people under the age of 50 have been infected with HSV-1-;the virus that causes oral herpes. In most cases it is asymptomatic, lying dormant within nerve cells. When activated, it can cause inflammation in nerves and skin, causing painful open sores and blisters. Most carriers-;and that’s one in two Americans according to the CDC-;will have between very mild to no symptoms before the virus becomes dormant. Varicella zoster virus is also extremely common, with about 95 percent of people having been infected before the age of 20. Many of those cases are expressed as chicken pox. VZV, which is a form of herpes virus, can also remain in the body, finding its way to nerve cells before then becoming dormant.
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