Large Study Found Flu and Common Virus Linked to Neurological Disease, but They May Not Be the Cause: Experts

Someone is diagnosed with the condition every four seconds. New research finds common virus infections are linked to developing a degenerative brain disease. But experts also have different opinions.

Common Virus Infections Associated with Neurological Disease Risk: Study

“We are seeing mounting evidence,” Heather Snyder, Alzheimer’s Association vice president of medical and scientific relations and who holds a doctorate in molecular biology, told The Epoch Times, “that microbes and/or viruses in the brain may be triggering or contributing to some type of immune reaction” that is related to the buildup of amyloid plaques and tau tangles—the hallmark of Alzheimer’s disease.

This is not limited to Alzheimer’s disease. Researchers at the National Institutes of Health (NIH) found an association between exposure to various viral diseases and an increased risk of many neurodegenerative diseases.

They analyzed data (pdf) from over 300,000 people in a Finnish biobank and nearly a half million people in the UK biobank.

These individuals had been diagnosed with different types of neurodegenerative diseases, including:

  • Alzheimer’s disease
  • Vascular dementia
  • Parkinson’s disease
  • Generalized dementia
  • Amyotrophic lateral sclerosis (ALS)
  • Multiple sclerosis (MS)

They were compared to people who hadn’t been diagnosed with any of these neurological diseases.

The result shows that patients who experienced influenza with pneumonia were more likely to develop five of the six diseases studied. Infection with the Epstein-Barr virus increased the risk of multiple sclerosis. Viral encephalitis was associated with an increased risk of Alzheimer’s disease, while shingles infection and intestinal viral infections were also associated with neurological disease.

About 80 percent of viruses looked at in the study were neurotrophic, meaning that they’re able to attack the central nervous system through peripheral nerves or by crossing the blood-brain barrier. These viruses might increase disease risk by causing brain inflammation that reduces our cognitive reserves.

However, researchers are unsure how long after infection people experience this increased risk.

“Although we are working with NDDs (neurodegenerative diseases) that generally occur in middle-aged to elderly study participants, it is unclear if viral exposures more than 15 years before NDD diagnosis contribute to risk,” the study authors said.

Dr. Bibhuti Mishra, chief of neurology at Long Island Jewish Forest Hills, part of Northwell Health in New York, said the study deserves attention because there is a huge amount of data.

Vaccination Against Flu and Pneumonia

The NIH researchers suggest using currently available vaccines for some of these viruses, including influenza, varicella-zoster (shingles), and pneumonia, to reduce neurodegenerative disease risk.

After COVID-19, questions regarding vaccines started to arise. But some physicians think vaccination against these common viruses could still help certain people to reduce risk.

Studies reported at the 2020 Alzheimer’s Association International Conference found that influenza and pneumonia vaccinations were associated with reduced risk of Alzheimer’s disease.

The first study looked at an American health record data set of more than 9,000 patients over 60 years old. The findings indicate receiving a single flu vaccination was linked with a 17 percent reduction in Alzheimer’s incidence. Those vaccinated more than once experienced an additional 13 percent reduction.

Another study researched the associations between receiving the pneumococcal (pneumonia) vaccine, with and without an accompanying flu shot, and Alzheimer’s risk. The findings suggest that receiving a pneumococcal vaccine between 65 and 75 years old could reduce Alzheimer’s risk by up to 30 percent after adjusting for factors like sex, genetics, race, birth cohort, education, and smoking habits. Among those vaccinated against pneumonia, who didn’t have any genetic risk factors for Alzheimer’s, there was up to a 40 percent reduction in risk.

Mishra said that vaccines could help, but many of the “worst offenders,” like viral meningitis and encephalitis, do not yet have vaccines.

Chicken and Egg

But is a viral infection the cause of neurodegenerative disease, or is it just a sign of a weakened immune system?

“The association is not proof of cause,” said Mishra. “Any infection will lead to inflammatory changes in the brain, and inflammation is already a significant presence in the brain of those who have neurodegenerative diseases, most prominently Alzheimer’s disease.”

He explained if you look at those infections that have the highest association with risk for neurodegenerative disease—viral meningitis and viral encephalitis—inflammation of the brain and brain membrane jump out with a 30- to 60-fold increased risk of neurodegenerative disease.

He thinks viral infection “can add fuel” to the fire of inflammation that makes neurodegenerative diseases worse.

“And the highest association between risk of worsening neurodegeneration and virus infection is within the first year after viral infection,” said Mishra. “This could imply that the neurodegeneration must be fairly advanced at the time of a severe viral infection (encephalitis or meningitis) to have the highest risk.”

Snyder noted that while viruses and bacteria are prevalent in our environment, and there are studies suggesting an increased presence of these factors in the brains of people with Alzheimer’s, the disease itself affects the immune system. “There are changes in the immune system as Alzheimer’s progresses and this may also be a contribution to why there is an increased presence,” she said.

Other factors that may potentially cause or contribute to Alzheimer’s disease progression include hypertension and diabetes, and these factors might also make individuals living with Alzheimer’s and related dementia more vulnerable to contracting viruses.

Additionally, dementia symptoms, such as forgetting to wash hands, can also put a person at higher risk.

“The takeaway message is: Take care of yourself,” said Snyder.

George Citroner reports on health and medicine, covering topics that include cancer, infectious diseases, and neurodegenerative conditions. He was awarded the Media Orthopaedic Reporting Excellence (MORE) award in 2020 for a story on osteoporosis risk in men.
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