Severe symptoms of COVID-19 are caused by brain infection in mice, finds study
Researchers found that SARS-CoV-2 persists in the brain after it is cleared in the lungs and concluded the severest and longest lasting symptoms of COVID-19 may be caused by brain infection.
Scientists suggest the long-term effects of COVID-19 may be as a result of the SARS-CoV-2 virus (which causes COVID-19) attacking the brain. According to the study’s lead researcher, their findings have implications for understanding the wide range in symptoms and severity of illness among humans who are infected by SARS-CoV-2.
“Our thinking that [COVID-19] is more of a respiratory disease is not necessarily true,” said the study’s lead researcher, Assistant professor Mukesh Kumar, from Georgia State University, US. “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 is the central processor for everything.”
In their study, published in Viruses, the researchers assessed the viral load in multiple organs of mice infected with SARS-CoV-2 via their nasal passages. A control group received a dose of sterile saline solution in their nasal passages.
They reported that following infection, there was a rapid, escalating attack on the brain that triggered severe illness, even after the lungs were successfully clearing themselves of the virus.
In the study, the viral load in the lungs of infected mice peaked three days after infection, then began to decline. However, the team observed very high levels of infectious virus in the brains of all the affected mice on the fifth and sixth days, which is when symptoms of severe disease became obvious, including laboured breathing, disorientation and weakness.
The study found virus levels in the brain were about 1,000 times higher than in other parts of the body.
Kumar said the findings could help explain why some COVID-19 patients seem to be on the road to recovery, with improved lung function, only to rapidly relapse and die. Both this, and other research, suggest the severity of illness and the types of symptoms experienced may be dependent on two factors – how much virus a person was exposed to and how it entered their body.
The nasal passages, he said, provide a more direct path to the brain than the mouth. He added that, while the lungs of mice and humans are designed to fend off infections, the brain is not. As a result, 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 is why we are 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.”
Kumar said that COVID-19 survivors whose infections reached their brain are also at increased risk of future health problems, including auto-immune diseases, Parkinson’s, multiple sclerosis and general cognitive decline.
He concluded that the scariest part of their findings is that people may never truly recover from the damage caused by COVID-19.