The coronavirus can reach the human brain after it is inhaled through a person’s nose and becomes trapped in the nasal mucus, a study found.
It is the first known evidence that the coronavirus can infect neurons of the brain through the mucosal pathway.
In the course of the pandemic, it has become clear that the coronavirus, called SARS-CoV-2, causes not only breathlessness, but also neurological problems.
For example, one in three report symptoms such as loss of smell or taste, headache, fatigue, dizziness, and nausea.
Scientists in Germany performed autopsies on 33 patients who died of Covid-19 and examined the mucus at the back of the nose – above the mouth where the throat joins the nasal cavity – as well as samples of brain tissue.
Coronavirus genetic material was present in greatest amounts in the nasal cavity mucus, but the SARS-CoV-2 spike proteins – which protrude from the virus and cling to human receptors to infect the cells – were also found in found the brain.
Dr. Frank Heppner, co-author of the Charité – Universitätsmedizin Berlin study, says, “Once in the olfactory mucosa, the virus appears to use neuroanatomical compounds, such as the olfactory nerve, to reach the brain.”
As part of the study, the academics managed to make the very first electron microscopy image of intact coronavirus particles in the mucus.
However, exactly how the virus reaches the brain from this point is not yet known, and further research is needed to unravel the mystery, the experts say.
“Our data suggests that the virus moves from nerve cell to nerve cell to reach the brain,” explains Dr. Helena Radbruch, one of the academics who collaborated on the study.
“However, it is plausible that the virus is also transported through the blood vessels, since the virus has also been found in the walls of blood vessels in the brain.”
As part of the research, the academics managed to make the very first electron microscopy image of intact coronavirus particles (red dots) in the olfactory mucus (photo)
The ability of SARS-CoV-2 to infect the brain is not unique among viruses, with herpes, influenza and rabies known to reach the mind through certain pathways.
The study, published today in Nature Neuroscience, also detected immune cells in the cerebrospinal fluid that were activated after infection.
Professor Heppner said: “In our view, the presence of the virus in nerve cells of the olfactory mucosa provides a good explanation for the neurological symptoms found in patients – such as loss of sense of smell or taste.
Covid-19 causes DELIRIUM in one in three elderly patients
Delirium is a common symptom of coronavirus in elderly patients, found in about one in three infected people over 65.
Researchers say delirium can be particularly harmful to the elderly, increasing their risk of serious illness and death.
The US-wide study looked at 817 elderly patients who tested positive for the coronavirus, 226 (28 percent) of whom were diagnosed with delirium.
The cohort had a mean age of 78 years and 84 (37 percent) of the delirious patients had no typical Covid symptoms – such as fever or shortness of breath.
Eighty-four delirious patients died in hospital, and scientists say delirium increases the risk of death by 24 percent and the chance of ICU admission by 67 percent.
Massachusetts General Hospital doctors worked with Harvard scientists to investigate any link between cases, deaths, and delirium.
Delirium is a condition that comes on suddenly, in which people become confused, have trouble thinking clearly and can hallucinate, become agitated or have mood swings.
‘We also found it in areas of the brain that control vital functions, such as breathing.
‘It cannot be ruled out that – in patients with severe Covid-19 – the presence of the virus in these areas of the brain will exacerbate respiratory function, contributing to respiratory problems due to an infection of the lungs.
“Similar problems can arise with regard to cardiovascular function.”
Professor Heppner told MailOnline that the presence of the virus in such critical areas of the brain could also cause the delirium reported in some patients.
But, he says, this could also be the result of a lack of oxygen in the brain caused by pneumonia and breathing difficulties.
“But certainly, since we found SARS-CoV-2 in areas of the brain that control breathing, the presence of SARS-CoV-2 can exacerbate such problems,” he says.
However, it is important to emphasize that the COVID-19 patients involved in our study had what is called a serious illness, belonging to that small group of patients whose disease proves fatal.
“So it is not necessarily possible to transfer the results of our study to cases with mild or moderate COVID-19.”
The findings help clarify what researchers have long suspected and offer new insight into a possible mechanism.
But Professor Gitte Moos Knudsen of Copenhagen University Hospital, who was not involved in the study, says the findings that SARS-CoV-2 jumps to the brain via the olactory nerve are not surprising.
“Entry into the central nervous system (CNS) through the nasal epithelium is a recognized mode of viral uptake and would not be unique to SARS-CoV-2,” she says.
“Overall, this doesn’t fundamentally change our current understanding of the mechanisms of action of this virus on the brain.”
Scientists say more research needs to be done on mucosal immunity to Covid-19
Much of the current scientific literature surrounding the coronavirus focuses on cellular immunity to the virus.
But the virus is easiest to detect in the nose and mouth, which is why lab-based swabs take samples here.
The mucosal immune system is the largest component of the immune system, say researchers at the University at Buffalo.
“We believe it is a serious omission to ignore the mucosal immune response to SARS-CoV-2, given the initial sites of infection,” says Dr. Michael W. Russell.
Clear the response of the systemic immunoglobulin G antibody [the most abundant circulating antibody] is important – we do not deny that – but it is insufficient in itself. ‘
“Considering that many infected people remain asymptomatic and that a large number of those who develop symptoms have only mild to moderate disease, this suggests that something somewhere reasonably good may be controlling the virus,” adds Dr. Russell.
“Could this be due to early mucosal immune responses that manage to control and eliminate the infection before it becomes severe?” he asked. “We won’t know unless these questions are answered.”
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