A large study, published in BMJ Open, adds to existing evidence of a link between herpes simplex virus 1 (HSV-1) infection and a heightened risk of Alzheimer’s disease. HSV-1 affects 64% of people under age 50 worldwide and is the main cause of oral herpes.

The research was conducted by the American biopharmaceutical company Gilead Sciences Inc. and Christine Johnston, MD, MPH, Professor in the Division of Allergy and Infectious Diseases at UW Medicine.

The team looked through a large database of US administrative medical claims and found that people diagnosed with herpes simplex 1 (HSV-1) were almost twice as likely to develop Alzheimer’s disease or a related dementia later in life. Those who had been prescribed antiviral treatment were less likely to have a diagnosis of Alzheimer's disease than those who did not receive that medicine.

“To me, the most interesting piece of this study is that we are finding similar data to what's been described in other studies of medical claim databases,” says Johnston. “Similar findings have been reported in studies of claims data from Taiwan, France, and Sweden, not only for the association of Alzheimer’s with HSV-1 diagnosis but also for the decreased risk of Alzheimer’s among those who received an antiherpetic medication.”

Looking at ICD-10 diagnostic codes in the database, the team found a total of 344,628 pairs of Alzheimer’s patients and control subjects with an average age of 73. Overall, 1,507 (just under 0.5%) people with Alzheimer’s disease had been diagnosed with HSV-1 (0.44%) compared with 823 (just under 0.25%) of those in the control group. While the risk of Alzheimer's disease in people age 65 and older in the general population is 10.8%, people in this study who had recorded HSV-1 infections ended up with a 19.8% risk.

The team looked at other viral infections and found similar patterns with herpes simplex virus 2, which causes genital herpes, and varicella-zoster virus, which causes shingles.

The researchers also looked for prescriptions of antiviral treatments for HSV-1 infection. Among the 2,330 people with a history of HSV-1 infection, 931 (40%) used medication for their symptoms. This group was 17% less likely to receive a diagnosis of Alzheimer’s disease than those who didn’t use these treatments.

There are limitations to what can be learned from claims data. The researchers do not have detailed information about the diagnoses of HSV-1 or the severity of symptoms in these cases. Most people with herpes infections have no symptoms or only mild symptoms, and this study only looked at people who sought medical care for their infections.

“What the results indicate is that we need to design perspective studies to understand the associations that we're seeing in many different countries,” Johnston says. A prospective study, which follows a group of people over time, would allow researchers to understand how herpes simplex infection affects Alzheimer’s risk and which populations would benefit from interventions and when.

Source: https://depts.washington.edu/mbwc/news/article/herpes-virus-alzheimers