Neurodegenerative diseases are diseases in which nerve cells in the brain and spinal cord gradually die over a long period of time. These diseases include Alzheimer’s, amyotrophic lateral sclerosis, Parkinson’s disease, and multiple sclerosis. Using information in the Finnish vital database FinnGen and a British database, the researchers identified 22 pairs of viral diseases in which infection with the virus is associated with an increased risk of developing such diseases. Viral encephalitis had the greatest impact on the risk of later Alzheimer’s disease. Influenza infection with pneumonia increased the risk of five of six neurodegenerative diseases. However, gastrointestinal infections or contact with the varicella zoster virus, which causes chickenpox and shingles, is also associated with an increased risk of diseases such as Alzheimer’s, MS or Parkinson’s. In some cases, the risk of disease remained high for 15 years after infection.
Vaccinations can protect
According to scientists, since some viral diseases such as influenza, chickenpox, and herpes zoster can be prevented by vaccination, they may at least partially reduce the risk of developing such neurodegenerative diseases. Virology professor d. Klaus Oberla of the University Hospital Erlangen points out that “before vaccinations can now be recommended to protect against neurodegenerative diseases, it will be important to prove that vaccinations actually reduce the frequency of neurodegenerative diseases.” In addition, the number of people vaccinated should be checked for the need to prevent a case of neurodegenerative disease. Therefore, the study is an important stimulus for further research.
More studies are necessary
In the study, links between infection and disease could be demonstrated in two different databases. However, this does not prove that viral infections are really responsible for neurodegenerative diseases. “It could be the case that, for example, people who tend to have severe viral infections also have an increased risk of developing neurodegenerative diseases,” Oberla says.
Nevertheless, the study is “relevant”, says Professor D. Martin Kurt, chair of the Neuroinflammation and Neurodegeneration Working Group at the Helmholtz Center for Infection Research in Braunschweig. In a mouse model, influenza viruses in particular were shown to also activate immune system cells in the brain that are suspected of damaging neurons over a longer period of time.
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