New Delhi: A new study conducted by scientists at the Yale University has suggested that the novel coronavirus, which primarily targets the lungs, may also affect the brain.
The study offers the first clear evidence on how the SARS-CoV-2 invades brain cells, “hijacks” them to make copies of itself and sucks up all of the oxygen nearby to starve neighbouring cells to death.
The study was posted online last week but has not yet been vetted by experts for publication.
‘Silent infection in the brain’
Scientists have found that unlike the zika virus, which also infects the brain, the novel coronavirus exploits brain cells’ machinery to multiply without destroying them.
When zika virus attacks the brain, the body’s immune cells flood the damaged sites and try to destroy infected cells. But no such response has been found in the case of coronavirus infection.
“It’s kind of a silent infection. This virus has a lot of evasion mechanisms,” Dr Akiko Iwasaki, the scientist leading the Yale research, told The New York Times.
The study has also found that the novel coronavirus reduces the number of synapses or connections between two nerve cells.
Speaking about synapses, Dr Alysson Muotri, a neuroscientist at the University of California, told The New York Times, “Days after infection, and we already see a dramatic reduction in the amount of synapses. We don’t know yet if that is reversible or not.”
How coronavirus enters brain
Earlier studies had suggested that the brain doesn’t have enough ACE2, a protein on the surface of a cell that is used by the coronavirus to infect. But the Yale study has found that the Covid-19 virus uses the same method to attack brain cells too.
The ACE2 protein occurs throughout the body but is especially present in the lungs.
The researchers have found that the virus may enter brain cells through the olfactory bulb, which regulates smell, via eyes as well as the bloodstream. They have also said virus infection in the brain can be more lethal than in the respiratory system.
For the study, the scientists had inserted ACE2 receptors in two sets of mice — one in the lungs and another in the brain. The brain-infected mice lost weight rapidly and died within six days, while the lung-infected ones didn’t die, and neither lost weight.
No clear picture on how common brain infection is
While Covid-19 patients have reported symptoms such as headaches and delirium, the scientists have now found more damaging effects that suggest brain infection.
Low blood oxygen from infected brain cells can cause strokes, they said. But strokes can also be caused by inflammation in the lungs that clog up blood vessels.
While the researchers have said scientific data is ahead of clinical evidence now, doctors will still need to study autopsy samples to see how common brain infection is and whether it is present in milder cases or severe ones.
According to Dr Michael Zandi, consultant neurologist at Britain’s National Hospital for Neurology and Neurosurgery in Britain, there is not much evidence of brain infection but doctors and scientists have known the possibility. “This data just provides a little bit more evidence that it certainly can,” he told The New York Times.
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