Being Infected With This Common Virus Could Trigger the Onset of Dementia, New Study Says


Once believed to be an inevitability of old age for some, researchers are now finding that in many cases, dementia is preventable. Interventions known to lower your dementia risk include exercising regularly, eating a healthy diet, quitting smoking, forgoing alcohol (or drinking in moderation), maintaining a healthy blood pressure, and treating other underlying conditions. Now, a new study has revealed yet another factor which may influence dementia risk: whether you have been infected with a common set of related viruses. Read on to learn how to lower your risk by avoiding this particular pair of illnesses for better brain health as you age.

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Being infected with this virus can trigger dementia, a new study says.
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Researchers from Tufts University and the University of Oxford published an important discovery this month in the Journal of Alzheimer's Disease. Using a 3D human tissue culture model of the brain, they demonstrated that the herpes simplex virus (HSV) can, under certain circumstances, trigger Alzheimer's disease—the most common form of dementia. In particular, they identified HSV-1, the type of herpes simplex that causes oral herpes, as responsible for initiating the onset of certain dementia cases.

However, the HSV-1 virus doesn't act alone. The researchers say that people infected with herpes simplex were only more likely to develop Alzheimer's disease only when they also became infected with the varicella zoster virus (VZV), a second herpes virus which commonly causes chickenpox and shingles. The researchers say that the presence of the second virus may "activate" herpes simplex "to set in motion the early stages of Alzheimer's disease."

READ THIS NEXT: If Your Handwriting Looks Like This, You Could Have Early-Onset Alzheimer's.

Here's how it happens.

Though researchers have been exploring the correlation between HSV-1 and Alzheimer's for decades, this new study outlines the "sequence of events that the viruses create to set the disease in motion," describing it as a "one-two punch" of viral infections.

"Our results suggest one pathway to Alzheimer's disease, caused by a VZV infection which creates inflammatory triggers that awaken HSV in the brain," Dana Cairns, PhD, a research fellow at Tufts and co-author of the study, said via press release. "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."

The study authors add that usually, HSV lies dormant in 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."

These viruses are both extremely common.

If it seems unlikely that a person might contract both viruses, consider the rates of infection. The World Health Organization (WHO) estimates that 3.7 billion individuals under the age of 50—or 67 percent of people in that age group—have been infected with HSV-1, but the majority of these cases are asymptomatic. Varicella zoster virus is also rampant. The study authors note that 95 percent of people become infected with VZV before the age of 20, causing chicken pox or shingles. Like HSV-1, VZV can also lay dormant—in this case in the nerve cells.

However, it's important to note that this combination of viruses only triggers dementia if they cause a particular inflammatory response. "The link between HSV-1 and Alzheimer's disease only occurs when HSV-1 has been reactivated to cause sores, blisters, and other painful inflammatory conditions," the study authors note.

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Getting vaccinated against VZV may reduce your dementia risk.
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Repeated activation of HSV-1 leads to increased brain inflammation, plaque productions, and cognitive damage resulting in dementia. Experts now suggest that you may be able to lower your dementia risk by becoming vaccinated against VZV, thereby preventing reactivation.

A second 2022 study published in the journal Alzheimer's and Dementia: Translational Research and Clinical Interventions corroborates this assertion. "We analyzed the association of shingles vaccination with incident dementia in those vaccinated in Wales between 2013 and 2020 in an observational cohort study using retrospectively collected national health data," researchers wrote. "People exposed to the vaccine had a 39 percent reduced hazard of dementia diagnosis after vaccination," they concluded.

However, VZV may not be the only catalyst that could reactivate dormant HSV. "It's still possible that other infections and other pathways of cause and effect could lead to Alzheimer's disease, and risk factors such as head trauma, obesity, or alcohol consumption suggest they may intersect at the re-emergence of HSV in the brain," said Cairns, via press release.

Speak with your doctor to learn more about how you can lower your dementia risk.