Bengaluru: Scientists in Germany have stated that patients infected with very severe Covid-19 can pass the coronavirus to their brains from noses.
The process occurs through infection in nasal mucus followed by subsequent hijacking of the olfactory nerve, and the authors deduced that the virus can enter the nervous system by crossing the neural-mucosal interface during an infection.
This is the first documented evidence of Covid transmission to the brain through the mucosal pathway.
The findings, published in the journal Nature Neuroscience on 30 November, were determined through autopsies conducted on 33 older patients who had died of the coronavirus.
Through the pandemic, it has been apparent that the SARS-CoV-2 virus causes not just respiratory troubles, but also neurological problems. These include headache, fatigue, brain fog, loss of focus, and confusion, but also nausea as well as anosmia or loss of smell.
To understand the trigger for these neurological symptoms, which are caused by the brain or nervous system getting affected, German scientists from Charité — Universitätsmediz in Berlin, conducted autopsies to study the mucus at the back of patients’ noses, in the area where the nasal cavity and the throat meet. This is the region where nasopharyngeal swabs are taken from for RT-PCR tests.
The scientists also studied samples of brain tissues taken from deceased individuals.
The team found that viral RNA material was present in the highest concentrations in the mucus present in the nasal cavity. This was determined by the first-ever electron microscopy image of intact coronavirus particles within the mucus as well. But antigens like the virus’s spike protein were detected in the brain.
Evidence of virus also found in walls of brain blood vessels
The authors also found SARS-CoV-2 spike protein in specific kinds of cells within the olfactory mucous layer, where it has the potential to pass through the endothelial and nervous tissue, subsequently into the brain.
Further, in some patients, the SARS-CoV-2 spike protein was found in neuron marker cells, implying that olfactory sensory neurons may be infected.
The spike protein was also found in parts of the brain that receive smell and taste signals. Evidence of the virus was also found in the walls of blood vessels in the brain.
Additionally, the researchers found the SARS-CoV-2 particles in other areas of the nervous system, including the medulla oblongata, which is the primary respiratory and cardiovascular control centre of the brain.
Not possible to apply results to mild cases
Infectious viruses crossing the blood-brain barrier and other kinds of nervous system defences to enter the brain is not new, albeit not common. Viruses like the rabies virus or even the flu virus have established pathways to affect the brain, leading to conditions like encephalitis or inflammation of the brain.
The authors of the study, however, emphasised that all the patients they performed autopsies on had a very severe case of the disease and died from it on an average of 30 days from the infection.
The average age of the deceased in the study was 71 years. Thus, they stressed that it is not possible to apply their results to mild or moderate Covid cases.