The brain as a puzzle as a symbol for diseases such as Alzheimer's (Photo: IMAGO, IMAGO / YAY Images)

Even long after a viral infection has survived, it can still burden the body, for example as chronic fatigue syndrome. Can diseases such as Alzheimer’s and multiple sclerosis also be promoted after viral infections? A new study suggests that, but it cannot answer crucial questions.

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In rare cases, a survived viral infection can result in chronic fatigue syndrome. In the case of the coronavirus, the long-term after-effects of a Covid-19 disease are referred to as Long Covid and Post Covid.

Like a new one Study in the journal Neuron shows, there could also be a connection between viral infections and neurodegenerative diseases such as dementia, Parkinson’s, Alzheimer’s or multiple sclerosis.

For their analysis, the researchers evaluated a total of 800,000 patient data from Finland and Great Britain. The data show a clear connection: If people had pneumonia, severe flu or encephalitis, the risk of dementia was increased. According to the data, there was still a higher risk of suffering from neurodegenerative diseases such as dementia, Parkinson’s, Alzheimer’s or multiple sclerosis up to 15 years after surviving a viral infection.

Are viral infections really the cause?

The study cannot say whether previous viral infections can actually cause dementia or whether people with impaired brain functions are simply more susceptible to viral infections. Initially, the patient data only shows that people who have survived infections are more likely to develop dementia or Alzheimer’s. The evaluations cannot make statements about the respective causes.

It is therefore also possible that people suffering from dementia develop viral infections more frequently in their lifetime – this could also result in the connection observed in the study. With regard to Alzheimer’s, there is already evidence that the disease breaks out in the body 20 years before the first symptoms appear.

Alzheimer’s and dementia are incurable diseases of the brain. Nerve cells in the brain are increasingly dying off in those who are ill, with the result that mental abilities such as memory or the ability to speak are impaired.

IMAGO / YAY Images

The study covers the last 15 years, so it is possible that some patients were already suffering from dementia or Alzheimer’s unnoticed at the time of the virus infection. That could at least be the case for some people, says neurobiologist Martin Korte from the TU Braunschweig.

An observation during the corona pandemic is similar. Martin Korte explains that people who had Alzheimer’s disease before a corona infection had a higher risk of a severe course of Covid 19. At least it cannot be ruled out that Alzheimer’s patients have a weaker immune system and therefore have to fight infections more often.

differences between Finland and Great Britain

In addition, a comparison of patient data from Finland and Great Britain showed that of 45 possible connections between individual viral diseases and various neurodegenerative diseases such as dementia and Alzheimer’s in the Finnish data, only 22 can also be confirmed in the data from Great Britain, says neurologist Klemens Ruprecht from the Charité in Berlin:

This suggests that some of the associations described could be false positive associations.

So viruses could actually cause dementia

On the other hand, there is evidence that certain viral infections can weaken the brain in the long term and thus promote new degenerative diseases such as dementia and Alzheimer’s. As neurobiologist Martin Korte explains, this is shown by several studies with mice. It is therefore assumed that microglial cells, i.e. the immune cells in the brain, could damage the nervous system for months.

We were already able to show in 2018 that a flu infection in particular also activates the immune system in the brain.

In addition, according to a published in the journal Science study After infection with the Epstein-Barr virus, the risk of contracting the neurological disease multiple sclerosis (MS) increases many times over. Since no other known risk factor for MS can explain the results, the study authors assume that the Epstein-Barr virus could be a major cause of multiple sclerosis. This study confirms that viral infections could actually promote neurodegenerative diseases.

Multiple Sclerosis (Photo: IMAGO, IMAGO / Panthermedia)

Multiple sclerosis (MS) is an inflammatory disease that affects the brain and spinal cord. In sick people, the immune system turns against their own body and damages nerve cells.

IMAGO / Panthermedia

Vaccination recommendations only after further investigations

If it is confirmed that previous viral infections increase the risk of neurological diseases such as dementia and Alzheimer’s, then vaccinations, for example against influenza or shingles, could become even more important, the research team writes in the study. However, before new vaccination recommendations can be made, the correlations found must be confirmed in further studies. It must therefore be shown clearly whether and how viral infections can trigger dementia or Alzheimer’s.

The study is an important impetus for further research in this direction, says virologist Klaus Überla from the University Hospital Erlangen. It is also important to show that vaccinations can indeed reduce the incidence of neurodegenerative diseases.

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J. A. Allen

Author, blogger, freelance writer. Hater of spiders. Drinker of wine. Mother of hellions.

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