Researchers have found that organoids (tiny tissue cultures made from human cells that simulate whole organs) known as "mini-brains" can be infected by the novel coronavirus that causes COVID-19.
The results, published in the ALTEX: Alternatives to Animal Experimentation, suggest that the virus can infect the human brain cells.
"This study is another important step in our understanding of how infection leads to symptoms, and where we might tackle the Covid-19 disease with drug treatment," said study lead author William Bishai from the Johns Hopkins University School of Medicine in the US.
Early reports from Wuhan, China, the origin of the Covid-19 pandemic, have suggested that 36 per cent of patients with the disease show neurological symptoms, but it has been unclear whether or not the virus infects human brain cells.
In their study, the Johns Hopkins researchers demonstrated that certain human neurons express a receptor, ACE2, which is the same one that the novel coronavirus uses to enter the lungs.
Therefore, they surmised, ACE2 also might provide access to the brain.
When the researchers introduced coronavirus particles into a human mini-brain model, the team found evidence of infection by and replication of the pathogen.
According to the researchers, the human brain is well-shielded against many viruses, bacteria and chemical agents by the blood-brain barrier, which in turn, often prevents infections of the brain.
"Whether or not the SARS-CoV-2 virus passes this barrier has yet to be shown. However, it is known that severe inflammations, such as those observed in Covid-19 patients, make the barrier disintegrate," said study senior author Thomas Hartung from the Bloomberg School of Public Health.
The impermeability of the blood-brain barrier, also can present a problem for drug developers targeting the brain, the study said.
"The mini-brains -- which model the growing human brain -- contain the ACE2 receptor from their earliest stages of development," the study authors wrote.
Therefore, the findings suggest that extra caution should be taken during pregnancy.
As of Wednesday morning, the overall number of global COVID-19 cases has increased to over 10.4 million, while the deaths have soared to more than 509,000.
The US accounted for the world's highest number of infections and fatalities with 2,629,372 and 127,322, respectively, according to Johns Hopkins University.