From Nasal Mucus, Up the Olfactory Nerve, to the Brain: Scientists Trace the Route of Severe Coronavirus Infections
After being inhaled through the nose, the coronavirus can reach an individual’s brain by passing from their nasal mucus to the olfactory nerve, a new study by German scientists has found.
Through the course of the pandemic, experts across the globe have noted that Covid19 causes not only respiratory distress but also neurological issues. The findings help explain why Covid19 patients often report loss of smell or taste, headaches, brain fog, fatigue, dizziness, and nausea.
“We know that many common respiratory infections, such as coughs and colds, can make us temporarily lose our sense of smell alongside a blocked nose or a sore throat. Previous research has shown that Covid19 is unusual in that being unable to smell can be the only symptom,” Tobias Welte, Past-President of the European Respiratory Society, had said in April.
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“Once inside the [nasal] mucosa, the virus appears to use neuro-anatomical connections, such as the olfactory nerve, in order to reach the brain…. In our eyes, the presence of the virus in nerve cells of the olfactory mucosa provides good explanation for the neurologic symptoms found in patients — such as a loss of the sense of smell or taste,” Dr. Frank Heppner, a neuropathologist at Charité–Universitätsmedizin Berlin who co-authored the study, told the media.
The novel coronavirus’ spike protein — or the viral membrane protein responsible for cell entry — was found within the mucus lining of the nose, in parts of the brain that receive smell and taste signals, as well as in the walls of blood vessels in the brain. In addition, the researchers also found Covid19 particles in other areas of the nervous system that serve as the primary respiratory- and cardiovascular-control center of the brain. This led them to the conclusion that the novel coronavirus infects the olfactory nerve after making its way there through the mucus, and proceed towards infecting neurons in the brain.
These findings help explain the variety of Covid19 symptoms. “It cannot be ruled out that — in patients with severe Covid19 — presence of the virus in these areas of the brain will have an exacerbating impact on respiratory function, adding to breathing problems due to infection of the lungs. … Similar problems might arise in relation to cardiovascular function,” Dr. Heppner added.
The researchers arrived at their findings through autopsies conducted on 33 patients who had died of the coronavirus. Hence, they caution that further studies might be needed to ascertain whether the findings can be applied to mild or moderate cases of Covid19.