Over 3,800,000,000 people have a common virus that may cause Alzheimer’s disease.
A top expert has pointed to a surprising link between Alzheimer’s disease and a common virus that nearly 3.8 billion people may already carry.
For over three decades, Professor Ruth Itzhaki, Emeritus Professor of Molecular Neurobiology at the University of Manchester, has studied this possible connection. Her research team discovered strong evidence tying Alzheimer’s to the herpes simplex virus type 1 (HSV-1)—the same virus that causes cold sores.
According to the World Health Organization (WHO), around 3.8 billion people under age 50 carry HSV-1. That’s nearly 64% of the global population. In fact, more than two-thirds of those under 50 have this virus.
WHO also explains that there are two types of herpes simplex virus: Type 1, which spreads through oral contact and causes cold sores around the mouth, and Type 2, which spreads through sexual contact and causes genital herpes.
HSV-1 usually spreads through skin-to-skin contact and leads to painful blisters or ulcers. While doctors can treat the virus, there’s no cure. It can stay dormant in the body for years without causing symptoms.
In a 1997 study, Professor Ruth Itzhaki and researchers at the University of Oxford found something striking. People with Alzheimer’s disease often carried a specific version of a gene—APOE-e4. When scientists examined the brains of individuals infected with HSV-1, they discovered the same abnormal proteins—amyloid and tau—that are hallmarks of Alzheimer’s.
The HSV-1 virus can stay dormant in the body for decades before reactivating. Professor Ruth Itzhaki explains that as people age and their immune defenses weaken, the virus can reach the brain and flare up. “Once it reactivates, it inflames and damages brain cells. These repeated flare-ups may eventually cause the kind of brain damage seen in Alzheimer’s disease,” she said.
This year, Professor Itzhaki took the theory further. Her research explored how head trauma might trigger the virus to wake up. In lab studies, mild brain injuries reactivated dormant HSV-1, sparking brain inflammation. That same inflammation closely mirrors the brain changes often found in Alzheimer’s patients.
Professor Ruth Itzhaki emphasized the urgent need to understand Alzheimer’s disease and dementia risk factors. She stressed that early awareness can lead to earlier prevention and targeted treatments.
Meanwhile, other scientists are also exploring the virus-dementia connection. In a recent study, researchers from the University of Texas Medical Branch found that people diagnosed with HSV-1 were 2.44 times more likely to develop dementia than those without the virus. This finding was based on electronic health records from about 120 million Americans.
Still, the full link between HSV-1 and Alzheimer’s needs more investigation. Experts say further clinical trials could unlock new strategies for preventing and treating dementia.
