Common viral illnesses could make you susceptible to brain decline

A study on 10 million U.S. soldiers prompted scientists to investigate further.
Ayesha Gulzar
MRI Brain Scan of head and skull
MRI Brain Scan of head and skull


Commonplace viral illnesses makes a person more susceptible to Alzheimer's disease and five other catastrophic neurodegenerative diseases (ND), according to a recent study published in Neuron. Unexpected connections were also found between Dementia, Parkinson's disease, multiple sclerosis (MS), Lou Gehrig's disease or amyotrophic lateral sclerosis (ALS), and vascular dementia.

An initial study focusing on blood test data of 10 million U.S. soldiers revealed that it's highly unlikely to get multiple sclerosis without first having an Epstein-Barr virus infection. These results impelled researchers at the United States National Institutes of Health Center for Alzheimer's and Related Dementias (NIH CARD) to investigate other significant associations between viral infections and NDs.

Troubling correlations were found according to an analysis of the medical records of almost a million people in Finland and the United Kingdom (UK).

Which viruses are linked to brain function decline?

The biomedical data scientists mined data from the medical records of 300,000 patients in the Finnish biobank, FinnGen, and 500,000 patients in the UK Biobank. According to the findings published in the journal Neuron, no less than 22 associations were found between a previous hospitalizing viral infection and neurodegenerative disorder diagnosis (NDD) five to 15 years post-infection.

Researchers were able to identify 45 significant infection-NDD associations in the FinnGen dataset. The UK Biobank was then examined for matches, and 22 associations could be replicated, which was the focus of the study.

A positive association was found between flu exacerbating to pneumonia and five of the aforementioned NDs, excluding multiple sclerosis. Individuals treated for encephalitis — brain inflammation—were almost thirty-one times more liable to develop Alzheimer's disease.

To elucidate, six percent of viral encephalitis patients developed Alzheimer's disease in the following years. Additionally, intestinal infections and the varicella-zoster virus (shingles) — a herpes virus that causes chickenpox — were also found to cause multiple neurodegenerative disorders.

Of the six NDs, dementia was revealed to have the most replicated associations. Eighty percent of the replicated associations resulted from neurotrophic viruses — viruses that invade the central nervous system through nerves in the brain's exterior and on the spinal cord. All viruses were found to increase the risk of NDs, and none were associated with a protective effect.

Could flu vaccines help against dementia?

While these findings appear staggering, the study possesses certain inescapable limitations. The data science-based approach investigates all possible links in one go. The resulting pairings are just data associations, and causal links cannot be confirmed. Susceptibilities due to genetics, age, lifestyle, and environmental factors are also not considered.

The study must also be expanded to those individuals who were infected but not hospitalized. NIH CARD head Andrew Singleton agrees that the mechanistic linking of viral exposure to ND pathogenesis requires rigorous follow-up research.

Nevertheless, the study highlights a topic that can significantly affect public health. It also champions the need for vaccines as they significantly reduce hospitalization rates. Fortunately, vaccines are available for some of the implicated viruses and may potentially mitigate the risk of developing NDs.

Influenza, pneumonia, and shingles vaccines have been found to reduce dementia. The role of vaccines, however, also requires more research to determine their efficacy in decelerating and perhaps precluding ND development.

This study was published in Neuron.

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