The virus that causes Covid-19 does not infect human brain cells, according to a study published in the journal Cell. The findings will raise hopes that the damage caused by Sars-CoV-2 might be more superficial and reversible than previously feared.
The study contradicts earlier research that suggested the virus infects neurons in the membrane that lines the upper recesses of the nose.
This membrane, called the olfactory mucosa, is where the virus first lands when it is inhaled. Within it are olfactory sensory neurons (OSNs), which are responsible for initiating smell sensations. They are tightly entwined with a kind of support cell called sustentacular cells.
In the new study, Belgian and German researchers claim that the virus infects sustentacular cells but not OSNs. “That is just a critical distinction,” said the senior author Peter Mombaerts, who directs the Max Planck Research Unit for Neurogenetics in Frankfurt, Germany. “Once you believe that olfactory neurons can be infected, there is a quick route into the olfactory bulb and then you’re in the brain already.”
The olfactory bulb, at the front of the brain, is where neural input about odours is first processed. If the virus penetrated this structure it could theoretically spread to deeper brain regions where it could do lasting damage – especially since, unlike OSNs, most neurons are not regenerated once lost.
But if the virus only infects the sustentacular cells, then the damage could be less long-lasting.