Medical Science

Flu in the head. A link between viral infections and neurodegenerative diseases has been established

Database pattern research has found associations between common viruses such as the influenza virus and neurodegenerative diseases such as Parkinson’s and Alzheimer’s, and amyotrophic lateral sclerosis (Lou Gehrig’s disease).

The results add to earlier discoveries linking individual viruses to specific diseases, such as the Epstein-Barr virus in people with multiple sclerosis. At the same time, experts draw attention to the fact that the new study is based on data from electronic medical records, not biological samples, and it simply describes correlations without proving a causal relationship between infection and disease.

The article, which was published by a team of researchers under the auspices of the US National Institutes of Health (NIH) in the journal Neuron, presents the results of a search for potential associations of a viral infection with neurodegenerative diseases in two large databases – the Finnish biobank FinnGen and the British UK Biobank. In the Finnish database, scientists identified 26,000 people with one of these diseases, and then checked the medical records of these people for signs of viral infections. In 45 cases, the authors found a clear combination of infection with brain disease, which means that people with brain disease are more likely to have a viral infection compared to 309,000 control people who do not have such ailments.

Continuing the study, the authors began to search for the same 45 “virus-disease pairs” in the UK Biobank database, which contains data on 500,000 people. The control cohort included data from 96,000 people. A UK database search returned only 22 of 45 associations, and these were the focus of further analysis. He showed that with all neurodegenerative diseases, except for multiple sclerosis, the flu, which turned into pneumonia, was most often associated.

The clearest association, a 31-fold increase in risk, was found between Alzheimer’s disease and viral encephalitis. In other cases, the increase in the likelihood of developing brain disease is more moderate. Thus, the common flu is associated with a five-fold increase in the risk of developing dementia. Almost all correlations between a virus and a neurodegenerative disease involve infection with neurotropic viruses, that is, those that enter the central nervous system. These are, in particular, herpes simplex and shingles viruses, as well as some strains of the influenza virus.

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