Uncommon Cold: Viral Infections Linked to Dementia, Alzheimer's Disease, Study Finds
Sometimes people can be laissez-faire about viral diseases, even thinking they can "walk it off". But one shouldn't forget that such illnesses can affect the nervous system, leading to severe consequences.
US researchers have analyzed the medical records of more than 400,000 people in the UK and Finland and found a correlation
between viral infection and the development of neurodegenerative diseases.
"We realized that for years scientists had been searching independently for links between an individual neurodegenerative disorder and a specific virus," said senior author Michael Nalls, a neurogeneticist at the National Institute on Aging in the US. "That's when we decided to try a different, more data/science-based approach. By using medical records, we were able to systematically search for all possible links in one shot."
In the first stage, the researchers studied the medical records of nearly 300,000 people stored in FinnGen, Finland's national database. They looked for people who had one of the following diagnoses: Alzheimer's disease, multiple or amyotrophic lateral sclerosis, generalized or vascular dementia, or Parkinson's disease. Then the team checked whether patients with these diagnoses had been previously hospitalized for a viral infection (except in the case of coronavirus infection). Initially, they found 45 associations between the diagnosis and a bad viral infection.
Then researchers turned to UK Biobank, a large UK database, and analyzed data from 96,000 people, 20,000 of whom had neurodegenerative disorders. Scientists focused on 22 reproduced associations.
The study showed that generalized dementia was the most common result of viral infection - particularly viral encephalitis, viral warts, all types of influenza and viral pneumonia. The strongest correlation was found between encephalitis and Alzheimer's disease: patients diagnosed with this viral disease were 31 times more likely to develop Alzheimer's later in life.
With data from the Finnish biobank, scientists estimated how the strength of the virus-disease link changes over time: one, five and 15 years after infection. Neurodegenerative diseases take a long time to develop, and one would expect the link to be stronger after 15 years. However, the researchers studied 16 pairs of associations, and for almost all pairs, the highest risk was within a year of infection with the virus and then decreased. Between five and 15 years, the high risk persisted for only six of these pairs.
"Nevertheless, the fact that commonly used vaccines reduce the risk or severity of many of the viral illnesses observed in this study raises the possibility that the risks of neurodegenerative disorders might also be mitigated," noted Dr Nalls.
Neurodegenerative disorders damage different parts of the nervous system. It usually occurs in adulthood or old age and causes problems with such actions as thinking, remembering, and moving.
Last year, a team of scientists conducted a study in which a study of 10 million medical records revealed a correlation between Epstein-Barr virus and the risk of multiple sclerosis.
Although the present study does not identify the cause-and-effect relationships that lead to neurological disorders, it gives an outline for the approximate boundaries of future research.