A recent study published in Science Advances has shed light on a previously unknown effect that SARS-CoV-2, the virus that causes COVID-19, has on brain cells. The study, conducted by researchers at the University of Queensland in Brisbane, Australia, along with colleagues at Macquarie University in Sydney and the University of Helsinki, Finland, found that the virus can cause different types of brain cells to fuse together, forming large masses of continuous cell 'blobs' called syncytia. This cellular fusion caused by SARS-CoV-2 infection could possibly affect information processing in the brain in both neurons and astrocytes.
However, it is important to note that these studies were conducted using cells in a laboratory setting and in human-derived brain organoids. Additional research needs to be done to understand if and how the effects observed in a dish translate to clinical effects experienced by humans. Neuronal syncytia have not yet been identified in patients that have passed away from COVID-19.
Prior studies suggested that SARS-CoV-2 can induce the fusion of other cell types. In some cases, autopsies of COVID-19 patients have shown syncytia in the lungs, which likely contribute to respiratory symptoms. Similar to other viruses, SARS-CoV-2 induced cell fusion may facilitate the spread of the virus within an organ without the need for it to infect new cells.
Although more research is needed, these results offer a plausible pathophysiological explanation for the effects of SARS-CoV-2 on the brain that might account for the cognitive effects of long-COVID. Meanwhile, scientists pointed out that neuronal fusion could be a relevant mechanism that other viruses that infect the brain take advantage of also, such as for example the rabies virus.