Link Between Common Germs and Dementia Risk

Recent research suggests that some common germs could potentially lead to dementia later in life. A study released today highlights a connection between various infectious diseases, especially herpes simplex-1 (HSV-1), and an increased risk of developing Alzheimer’s disease.

This study, conducted by scientists at Gilead Sciences and featured in BMJ Open, evaluated medical records of insured Americans. It found that individuals diagnosed with Alzheimer’s, as well as related conditions, had a higher likelihood of being diagnosed with HSV-1. These findings contribute to a growing body of evidence indicating that addressing and treating HSV-1 and similar viruses may help mitigate dementia risks.

Alzheimer’s is the most prevalent type of dementia, impacting around 7 million people in America. It generally arises from a complicated interplay of environmental and genetic factors. In recent years, several studies have pointed to infections—including HSV-1—as influential in this equation. Though HSV-1 primarily causes oral herpes or cold sores, it’s notable that many infected individuals show few or no symptoms, and it can also lead to genital herpes, primarily linked to HSV-2.

However, not all research has backed this viral association. To further explore the connection, the authors investigated it using real-world data. Lead researcher Luke Liu noted that this marks the first time a comprehensive database of U.S. insurance claims has been utilized to examine the relationship between Alzheimer’s and HSV-1.

The team compared nearly 400,000 people diagnosed with Alzheimer’s against a matched group without the disease based on age, gender, and other factors. Interestingly, although less than 0.5% of those with Alzheimer’s previously had an HSV-1 diagnosis, this rate was still notably higher than in the control group—about 80% more likely, in fact.

Upon examining a broader demographic with different forms of dementia tied to Alzheimer’s, researchers found similar trends. They also identified links between Alzheimer’s and two additional herpesviruses, herpes simplex-2 and varicella zoster virus, responsible for chickenpox and shingles. Surprisingly, those receiving antiviral treatment for HSV-1 appeared less likely to develop Alzheimer’s compared to untreated individuals, which is worth noting since antivirals can manage and reduce outbreaks but don’t cure the infection.

While observational studies can’t definitively prove causation between HSV-1 and Alzheimer’s, the accumulating evidence for such a link seems to be strengthening.

“Herpesvirus exposure likely correlates with Alzheimer’s disease and other forms of dementia, and antiviral medications may offer protective benefits,” Liu, a virologist at Gilead, shared in an email.

Nonetheless, significant questions remain about this association, particularly the underlying mechanisms. Some studies have indicated that our brain’s immune response might produce amyloid beta and tau proteins to combat herpesvirus infections, as these misfolded proteins contribute significantly to Alzheimer’s. There could be more intricate ways that HSV-1 and similar viruses trigger or worsen the condition.

It’s essential to acknowledge that many individuals contract HSV-1 throughout their lives without ever developing Alzheimer’s. About two-thirds of the global population under 50 carries HSV-1, as per the World Health Organization. The researchers discovered that the link between HSV-1 and Alzheimer’s was notably stronger among older adults, and there are indications that individuals with the ApoE-ε4 allele—a genetic variant linked to higher Alzheimer’s risk—may also be more vulnerable to HSV-1 infections. So, it seems these viruses could be among various triggers leading to Alzheimer’s.

Despite this, overall evidence suggests that managing certain infections can significantly lower dementia risks. Various studies have established a relationship between shingles vaccination and reduced incidence of Alzheimer’s. Future clinical trials exploring whether antiviral treatments for herpes can minimize dementia risk may be required, although Liu notes that such research demands considerable resources. Ongoing efforts are also in place to create vaccines for HSV-1 and HSV-2, which might turn out to be more valuable than previously considered.

“These findings underscore the importance of viewing the prevention of herpesviruses as a public health priority,” the researchers concluded.