Neurological impact of covid-19 - Part 24 Jul 2021 14:56
Is covid-19’s effect on the brain unusual?
Not particularly. Many other viruses, including the measles, polio and Zika ones, can also affect the brain. For instance, hospitalisation with pneumonia, which can be caused by viral infection, can lead to cognitive impairment that lasts at least a year in a third of those over 60 and a fifth of younger people.
How does the damage actually occur?
The coronavirus can infect the cells lining the blood vessels that supply the brain, says Frank Heppner at Charité University of Medicine in Berlin, causing inflammation and potential complications such as strokes. But the virus doesn’t seem to cross the blood-brain barrier and attack brain tissue directly.
When Andreas Keller at Saarland University in Germany and his colleagues examined eight people who died of covid-19, they found major changes in gene expression characteristic of those seen in neurodegenerative conditions such as Alzheimer’s disease. They think that certain signalling molecules, triggered by the virus, relay information into the brain and cause inflammation and other damage that could help explain symptoms such as the brain fog and fatigue many report.
Can covid-19 lead to Alzheimer’s?
As part of a long-term study called the UK Biobank, the brains of 40,000 people had been scanned before the pandemic. Now 800 of those people, 400 of whom tested positive for the virus, have been rescanned. The results show a loss of grey matter in some parts of the brains of those infected, including in younger people and those with only mild disease.
A preprint describing these findings has raised alarm bells with some (medRxiv, doi.org/gkx6). “It’s very concerning,” Scott Gottlieb, former head of the US Food and Drug Administration, told CBS News. “It suggests… covid is a disease that could create persistent symptoms.” The researchers aren’t discussing the results yet.
Michael thinks that direct infection of the olfactory nerve is causing damage that then affects adjacent areas of the brain, including memory regions.
What has most alarmed people is the possibility that this brain damage could lead to later consequences. The preprint states that the findings raise the possibility that SARS-CoV-2 infection “might in time contribute to Alzheimer’s disease or other forms of dementia”.
Other researchers say this is plausible, but think at worst it will affect a tiny number of people. “We cannot exclude the possibility,” says Heppner. But many viruses have similar effects on the brain without causing such conditions, he says. “It won’t apply to every covid patient for sure.”
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