Researchers have found that infecting the nasal passages of mice with the virus that causes Covid-19 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 researchers, including an Indian-origin researcher, the 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 it's more of respiratory disease is not necessarily true. 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," said lead researcher Mukesh Kumar, Assistant Professor, Georgia State University in the US.
The study, published by the journal Viruses, assessed virus levels in multiple organs of the infected mice. A control group of mice received a dose of sterile saline solution in their nasal passages.
His team found that virus levels in the lungs of infected mice peaked three days after infection, then began to decline.
However, very high levels of infectious virus were found 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.
The researcher 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.
His research and other studies suggest the severity of illness and the types of symptoms that different people experience could depend not only on how much virus a person was exposed to but how it entered their body