Biology researchers at Georgia State University think we might not be looking at COVID-19 the right way.
In a recent study, they found infecting mice with the coronavirus through their nasal passages led to a “rapid, escalating attack on the brain that triggered severe illness, even after the lungs were successfully clearing themselves of the virus,” according to a press release.
The study’s lead researcher, assistant professor Mukesh Kumar, said the findings could help to understand better the wide range in symptoms and severity of the disease among those infected by SARS-CoV-2, the virus that causes COVID-19.
“Our thinking that it’s more of a respiratory disease is not necessarily true,” Kumar said. “Once it infects the brain it can affect anything because the brain is controlling your lungs, the heart, everything. The brain is a very sensitive organ. It’s the central processor for everything.”
The GSU study, published today in the journal Viruses, found that after injecting mice through their nasal passages, virus levels in their lungs peaked after about three days, then declined. The researchers found virus levels in the brains, however, on the fifth and sixth days, which they say is when symptoms of severe disease became obvious.
The scientists also found virus levels in the brain were about 1,000 times higher than in other parts of the body.
Credit: Photo courtesy of Georgia State University
Credit: Photo courtesy of Georgia State University
According to Kumar, the findings could help to explain why some COVID-19 patients seem to be recovering — with improved lung function — only to rapidly relapse and die. His research suggests it’s not only how much virus a person is exposed to, but also how it entered their body, that determines what symptoms they experience and how severe the disease is.
Nasal passages, he said, are a more direct path to the brain. And while the lungs of mice and humans are designed to fend off infections, the brain is ill-equipped to do so, Kumar said. Once viral infections reach the brain, they trigger an inflammatory response that can persist indefinitely, causing ongoing damage.
“The brain is one of the regions where virus likes to hide,” he said because it cannot mount the kind of immune response that can clear viruses from other parts of the body. “That’s why we’re seeing severe disease and all these multiple symptoms like heart disease, stroke and all these long-haulers with loss of smell, loss of taste. All of this has to do with the brain rather than with the lungs.”
This isn’t the first study to look at nasal passages as a key entry point for the coronavirus.
This past August, scientists at Johns Hopkins University reported the “hook” of cells used by SARS-CoV-2 to latch onto and infect cells is found up to 700 times more in cells lining the inside of the upper part of the nose than in the cells lining the rest of the nose and the windpipe. These supporting cells are necessary for the function and development of odor-sensing cells.
It’s why they urge everyone to wear a face covering correctly — making sure to cover both your mouth and nose.
Kumar said COVID-19 survivors whose infections reached their brain have a higher risk of autoimmune diseases, Parkinson’s, multiple sclerosis and general cognitive decline.
“It’s scary,” he said. “A lot of people think they got COVID and they recovered and now they’re out of the woods. Now I feel like that’s never going to be true. You may never be out of the woods.”
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