Now, scientists might know why.
The coronavirus has been found to be able to enter brain cells and replicate, which helps explain the neurological symptoms some patients experience, according to a preliminary study that was posted on the preprint server bioRxiv.
For the study, a team of researchers at Yale University closely examined coronavirus brain infections by looking at mouse models, brain cells in petri dishes, and brain tissue samples from a deceased coronavirus-positive patient.
What they discovered was that SARS-CoV-2, the virus that causes the coronavirus, not only has the ability to enter the brain but can also take over brain cells in order to make copies of itself.
The contagion also appears to deprive nearby cells of oxygen, causing them to wither and die.
It is still unclear how the virus travels to the brain or who will most likely be targeted. Some individuals may be more susceptible due to their genetic makeup or the viral load they’re exposed to, the researchers noted.
“If the brain does become infected, it could have a lethal consequence,” the study’s lead author Dr. Akiko Iwasaki, an immunologist at Yale University, told the New York Times.
The data from the research, however, point toward that infection of the brain is likely rare.
Other pathogens, such as the Zika virus, are also known to infect brain cells. Immune cells then rush to the damaged sites and try to destroy the infected cells.
The coronavirus, though, operates differently, as it takes advantage of the brain cells’ makeup to replicate—but doesn’t destroy them.
“It’s kind of a silent infection,” Iwasaki said. “This virus has a lot of evasion mechanisms.”
The coronavirus can infect a cell via a protein on its surface called ACE2, which is present throughout the body and especially in the lungs. Previous research has shown that the brain lacks high levels of ACE2, making a direct invasion unlikely.
But as Iwasaki and her colleagues looked more closely, they eventually discovered that the contagion could indeed enter brain cells through that particular protein.
“It’s pretty clear that it is expressed in the neurons and it’s required for entry,” Iwasaki said.
It also has been hypothesized that the nose could provide an avenue to the brain, but the authors wrote that this needs to be validated through more studies.
Now more than eight months into the pandemic, there are roughly 27.9 million confirmed cases of coronavirus worldwide, including at least 905,000 related deaths, according to the latest data from Johns Hopkins University.
Ethen Kim Lieser is a Minneapolis-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek and Arirang TV. Follow or contact him on LinkedIn.