40% of mice were found to have infectious SARS-CoV-2 and viral RNA in their brain tissue. However, 60% had no infectious virus and low levels of viral RNA present. Only 1/6 animals was SARS-CoV-2+ in its brain tissue 7 days after infection (dpi = days post infection). The virus was found throughout the cerebral cortex and seemed to avoid the olfactory bulb and cerebellum. This suggests that SARS-CoV-2 can cross the blood-brain barrier and does not travel across the cribriform plate to infect neuronal processes near the initial infection site in the nose.

Figure: SARS-CoV-2 RNA staining (red) of one infected mouse brain. RNA is present in the cerebral cortex, and not in cerebellar or olfactory tissue.