The findings, published in the journal Brain, suggest that the neurological changes often seen in these patients may result from inflammation triggered by the virus in other parts of the body or the brain’s blood vessels.
“We’ve looked at more brains than other studies and we have used more techniques to search for the virus. The bottom line is that we find no evidence of viral RNA or protein in brain cells,” said researcher James E. Goldman from Columbia University.
For the study, the research team examined the brains of 41 patients with Covid-19 who succumbed to the disease during their hospitalization. The patients ranged in age from 38 to 97, about half had been intubated and all had lung damage caused by the virus.
All of the patients had extensive clinical and laboratory investigations, and some had brain MRI and CT scans.
To detect any virus in the neurons and glia cells of the brain, the researchers used multiple methods including RNA in situ hybridization, which can detect viral RNA within intact cells; antibodies that can detect viral proteins within cells; and RT-PCR, a sensitive technique for detecting viral RNA.
Despite their intensive search, the researchers found no evidence of the virus in the patients’ brain cells. Though they did detect very low levels of viral RNA by RT-PCR, this was likely due to virus in blood vessels or leptomeninges covering the brain.
The tests were conducted on more than two dozen brain regions, including the olfactory bulb, which was searched because some reports have speculated that the coronavirus can travel from the nasal cavity into the brain via the olfactory nerve.
“Even there, we didn’t find any viral protein or RNA. Though we found viral RNA and protein in the patients’ nasal mucosa and in the olfactory mucosa high in the nasal cavity,” Goldman said.