A large U.S. study found that adult patients diagnosed with herpes simplex virus type 1 were more likely to develop Alzheimer’s disease, especially those aged 75 years and older.
The findings also showed that patients with herpes simplex virus type 1 (HSV-1) who received antiviral medication had a lower risk of developing Alzheimer’s disease compared with those who did not.
In the study, investigators analyzed health insurance claims from over 344,000 patients with Alzheimer’s disease and matched them 1:1 to controls without neurologic disease based on age, sex, region, and health care utilization. All participants were aged 50 years or older.
Among those with Alzheimer’s disease, 0.44% had a prior HSV-1 diagnosis compared with 0.24% of controls. After adjusting for comorbidities, the investigators found that HSV-1 was associated with an 80% increased risk of Alzheimer’s disease. The risk rose with age: the odds ratio (OR) was 1.14 for ages 50 to 70 years, 1.51 for ages 71 to 74 years, and 2.10 for those 75 years and older.
In a subset of patients with HSV-1, those treated with antiviral medications such as acyclovir or valacyclovir had a 17% lower risk of developing Alzheimer’s disease compared with untreated patients, based on a Cox proportional hazards model.
“[Patients] treated with antiherpetics had a significantly decreased risk of [Alzheimer's disease],” said lead study author Yunhao Liu, PhD, of Gilead Sciences, and colleagues.
The findings support prior studies linking certain viral infections to neurodegenerative diseases. While the mechanisms remained under investigation, evidence suggested that HSV-1 may promote brain inflammation or trigger immune responses that contribute to Alzheimer’s disease pathology.
The investigators also examined other herpesviruses. Both herpes simplex virus type 2 (HSV-2) and varicella zoster virus (VZV) were more common among patients with Alzheimer’s disease. In contrast, cytomegalovirus (CMV) showed no statistically significant difference between groups.
Because the analysis relied on health insurance claims data, it captured only patients diagnosed and treated in clinical settings. The investigators noted that since HSV-1 infections are often asymptomatic, many cases may go unreported, meaning the true prevalence could be higher.
Despite this limitation, the results were consistent with previous studies conducted in other populations and regions. The investigators suggested that identifying HSV-1 infections and evaluating the use of antiviral therapies could have implications for long-term brain health in older adults.
Full disclosures are available in the published study.
Source: BMJ Open