The coronavirus mainly targets the lungs, but also the kidneys, liver and blood vessels. However, about half of patients report neurological symptoms, including headaches, confusion, and delirium, suggesting that the virus may also attack the brain.
A new study provides the first clear evidence that, in some people, coronaviruses invade brain cells and hijack to make their own replicas. The virus also draws in all the oxygen nearby, starving neighboring cells.
It is unclear how the virus enters the brain or how often it sets up this trial of destruction. Brain infections are rare, but some people may be susceptible to their genetic background, high viral load, or other reasons.
Akiko Iwasaki, an immunologist at Yale University who led the work, said that if the brain became infected, it could have fatal consequences.
The study was posted online on Wednesday and has not yet been checked for publication by experts. But some researchers said it was cautious and grandiose, showing in many ways that the virus could infect brain cells.
“Scientists had to rely on brain images and patient symptoms to have an effect on the brain, but we did not really see enough evidence that the virus could infect the brain,” said the doctor. Michael Zandi, Consultant Neurologist at the National Hospital for Neurology and Neurosurgery in Britain. “This data provides a bit more evidence that it certainly can.”
Dr Zandi and his colleagues published research in July showing that some patients with Covid-19, a disease caused by coronavirus, develop serious neurological complications, including nerve damage.
In the new study, Dr. I. Iwasaki and his colleagues documented brain infections in three ways: in the brain tissue of a person who died in Covid-19, in a mouse model, and in the orgoids – clusters of brain cells in a lab dish. Copy the three-dimensional structure of the brain.
Other pathogens – including the Zika virus – are known to infect brain cells. Immune cells then flood the damaged sites, trying to cleanse the brain by destroying infected cells.
Coronavirus is very stealthy: it absorbs brain cells to multiply machinery, but does not destroy it. Instead, it cuts off oxygen to nearby cells, causing them to die and die.
Researchers have found no evidence of an immune response to this problem. Dr. “This is a kind of silent infection,” Iwasaki said. “There are a lot of scattered mechanisms in this virus.”
These findings are consistent with other observations of organoids infected with the coronavirus, said Assan Muotri, a neuroscientist at the University of California, California, who studied the Zika virus.
The number of coronavirus synapses seems to decrease rapidly in the connections between neurons. “The days after the infection, and we’ve already seen a dramatic reduction in the amount of synapses,” Dr. Mu. Muotri said. “We don’t know yet whether it is reversible or not.”
The virus infects the cell with a protein on its surface called ACE2. Those proteins appear throughout the body and especially in the lungs, explaining why they prefer the target of the virus.
Previous studies suggest that, depending on protein level proxies, the brain has low ACE2 and is more likely to survive. But Dr. I. Iwasaki and his colleagues looked more closely and discovered that the virus could actually enter brain cells using this door.
“It is very clear that it is expressed in neurons and it is necessary for penetration,” said Dr. I. Iwasaki.
His team then looked at two sets of mice – one with ACE2 receptors expressed only in the brain, and the other with only receptors in the lungs. When they introduced the virus to these rats, the brain-infected rats quickly lost weight and died within six days. Even rats with lung infections did not.
Dr. Despite the warnings associated with the mouse study, the results suggest that a virus infection in the brain may be more fatal than a respiratory infection, Iwasaki said. Iwasaki said.
The virus reaches the brain through the eyes or through the bloodstream – through the olfactory bulb – which controls odor. It is not clear which path the pathogen is taking, and whether it is often enough to explain the symptoms seen in people.
“I think this is a case where scientific data goes beyond clinical evidence,” Dr Mu said. Muotri said.
Researchers will need to analyze many autopsy specimens to estimate how common a brain infection is and whether it is present in people with mild disease or in so-called long-haired people with many of these neurological symptoms.
Dr. Jovis Hopkins University neurologist. Forty to 60 percent of Kovid-19 patients experience neurological and psychiatric symptoms, Robert Stevens said. But symptoms may not be all caused by viruses that invade brain cells. It can be the result of widespread inflammation throughout the body.
For example, inflammation in the lungs can release molecules that make the blood sticky and close the blood vessels, leading to stroke. Dr. Zandi said that there is no need for brain cells to be infected for that.
But in some people, he added, there may be a lack of blood oxygen from infected brain cells that trigger a stroke: “Different groups of patients may be affected in different ways.” “It’s quite possible that you’ll see a combination of the two.”
Some cognitive symptoms, such as cerebral palsy and delirium, may be more difficult to treat in patients sitting and on a ventilator. Doctors should plan to dial sedatives once a day, if possible, to evaluate Covid-19 patients, Dr. Stevens said.
