Coronavirus: One of the coronavirus’s most unexpected tricks is its ability to cause neurological symptoms, including dizziness, headaches and the blunting of taste and smell. Traces of the virus have shown up in brain tissue, examined post-mortem, but scientists don’t know exactly how the virus got there, much less how it might alter neurons’ function.

A new study, based on autopsies of people who died of Covid-19, provides some of the first clues. The virus may spread to the brain through the nose, where it can invade nerve endings deep in the nasal passages. If further tissue analysis is supportive, the findings should help explain how the virus reaches circuits in the brain that support perception, balance and mental acuity.

In the paper, posted Monday by the journal Nature Neuroscience, a research team based in Berlin produced the first images of intact coronaviruses in the so-called nasopharynx, where the throat meets the nasal cavity, and where odor receptors and perceptual cells converge.

The virus can enter the nervous system “by exploiting the close vicinity of olfactory mucosal, endothelial and nervous tissue, including delicate olfactory and sensory nerve endings” in the mucous layer of the nasopharynx, the authors conclude.

Up to a third of people who fall ill from Covid-19 report at least one neurological deficit, whether in taste, smell, balance or alertness. These symptoms are often transitory, but they are common enough to suggest that people with severe forms of the disease should show some evidence of infection in their central nervous systems.

In the new report, a research team led by Dr. Helena Radbruch and Dr. Frank Heppner, neuropathologists at the Charité-Universitätsmedizin, in Berlin, studied tissue samples from 33 people who had died after contracting Covid-19. The samples came from four areas of the brain, and from the olfactory mucosa, the mucous membrane of the nasopharynx.

The analysis found evidence of the virus in various parts of the brain, and in the olfactory mucosa, where its concentration was highest. Deep in this layer, near nerve endings that project to the brain, the researchers found the coronavirus’s signature spike protein, which it uses to attach to and infect cells.

Taken together, the findings suggest that the virus is “able to use the olfactory mucosa as a port of entry into the brain,” said Dr. Heppner, in a prepared statement.

The authors cautioned that their findings apply only to people with severe disease, and not necessarily to the majority of people infected, who experience modest symptoms, if any.
— Benedict Carey The New York Times