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The coronavirus mainly attacks the lungs, but also the kidneys, liver and blood vessels. However, about half of the patients also report neurological symptoms. These include headaches, confusion, and even delirium. These symptoms indicate that the virus is likely to attack the brain as well.
A new study brings to light the first clear evidence that in some people the coronavirus invades the brain cells in which it reproduces. The virus also appears to absorb all the oxygen around it, leaving neighboring cells to suffocate.
It is not known with certainty how the virus reaches the brain or how often it destroys brain cells in this way. Brain infections are probably rare. But some people may be more vulnerable due to a genetic predisposition, a high viral load, or other causes.
“If the brain is really infected, the result can be death,” warns Akiko Iwasaki, an immunologist at Yale University and lead author of the study.
The study was published online Wednesday and has not yet been peer-reviewed for official publication. But several researchers say he was meticulous and elegant, showing in many ways that the virus can infect brain cells.
The scientists relied on encephalograms and symptoms of the patients to deduce the effects of the virus on the brain. “This evidence provides some additional evidence that the coronavirus will surely infect the brain,” he said. Michael Zandi, a consultant neurologist at the National Hospital for Neurology and Neurosurgery, UK.
Dr. Zandi and his colleagues published a study in July showing that some coronavirus patients develop severe neurological problems, including nerve damage.
In a new study, Dr. Iwasaki and his colleagues recorded the infection in the brain in three ways: in brain tissue from a dead coronavirus, in a mouse model, and in organoids, clusters of brain cells on a stone plate that mimic the three-dimensional structure of the brain.
Other pathogens, such as the Zika virus, are known to infect brain cells. The immune cells then flood into the damaged areas and try to help the brain by destroying the infected cells.
The coronavirus is much more “stealthy”: it exploits the mechanisms of brain cells to reproduce, without destroying them. Instead, it absorbs all the oxygen from adjacent cells, killing them.
The researchers found no evidence of an immune response to the problem. “It is a silent infection,” explains Dr. Ivasaki. “This virus has many invasive mechanisms.”
These findings are consistent with other observations in organs infected with the virus, explains Allison Muwattri, a neuroscientist at the University of California, San Diego, who has also studied the Zika virus.
The coronavirus seems to rapidly reduce the number of synapses, that is, the connections between neurons. “Days after infection, we are already seeing a drastic reduction in the number of contractions,” explains Muotri. “We still don’t know if this is reversible or not.”
The virus infects a cell through a protein on its surface, ACE2. This protein is present throughout the human body, but mainly in the lungs. That is why your virus is weak.
Previous studies have suggested that the brain has very little protein of this type, which makes it possible for it to be safe.
But Dr. Iwasaki and his colleagues found that the virus could in fact use this medium to enter the brain.
The team then tested two groups of mice: one with the ACE2 receptor only in the brain and another with the same receptor only in the lungs. When the scientists introduced the virus into these mice, the infected ones in the brain rapidly lost weight and died within six days. The others did not suffer either.
“Despite the limitations of the mouse research, the results still show that brain infection is more deadly than respiratory infection,” he said. Ivasaki.
The virus can reach the brain through the olfactory bulb, which controls smell, through the eyes, or even through the bloodstream. Of course, this is not the path the pathogen follows, even if it follows it often enough to explain the symptoms that occur in multiple patients.
Scientists must analyze multiple autopsy samples to assess how common the infection is in the brain and whether it is present in people with milder symptoms or only in those who have been ill for a long time, having in many cases also exhibited neurological symptoms.
Although 40-60% of patients treated with coronavirus have neurological and psychiatric symptoms, it is not certain that all are the result of invasion of the virus into brain cells. It can be the result of prolonged inflammation throughout the body.
For example, inflammation of the lungs can cause a blood clot that can lead to a stroke.
Other symptoms, such as confusion or delirium, may not always be present in sedated or intubated patients.
Source: www.nytimes.com
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