An estimated 3.7 billion people worldwide have herpes simplex virus 1 (HSV1), according to the World Health Organization. Now, new research published in the medical journal Frontiers in Ageing Neuroscience suggests that this type of herpes—known to cause cold sores—is a major risk for Alzheimer’s disease (AD) and may account for 50 percent of cases, reports Medical News Today.

AD is a type of irreversible dementia that slowly destroys cognitive abilities.

For the study, Ruth Itzhaki, PhD, a professor at the University of Manchester in the United Kingdom, examined three recent studies on the association between AD and HSV1 or chickenpox (caused by a different kind of herpes virus) using population data from Taiwan. (The nation enrolls almost all of its citizens in the National Health Insurance Research Database, which provides researchers with comprehensive health information for their work.)

Findings showed strong evidence that people with herpes viruses face a greater risk of developing senile dementia. Furthermore, the results suggested that antiviral medication could dramatically decrease dementia risk in those who have severe HSV1.

“Considering that over 150 publications strongly support an HSV1 role in Alzheimer’s, these findings greatly justify usage of anti-herpes antivirals—which are safe and well tolerated—to treat Alzheimer’s disease,” Itzhaki said. “They also incentivize the development of an HSV1 vaccine, which would likely be the most effective treatment.”

Itzhaki previously found that cold sores triggered by HSV1 were more frequent among people who carried a gene variant known as APOE-e4 that may increase a person’s risk of developing Alzheimer’s. “HSV1 could account for 50 percent or more of Alzheimer’s cases,” she said.

Despite the results showing a relationship between HSV1 and Alzheimer’s, however, more studies must be conducted to confirm that the first causes the latter.

Next, Itzhaki plans to study dementia rates among people with mild HSV1 or mild genital herpes, since this inquiry focused only on the connection between the condition and severe cases of herpes simplex virus 1 and chickenpox infections. 

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