Coronaviruses in the Covid-19 brain can also trigger psychoses
A new study now provides the first clear evidence that the coronavirus enters brain cells in some people. The study by US and British immunologists and neurologists has so far only been published as an unchecked pre-print. The research group examined whether the Sars-CoV‑2 can infect the brain and what consequences an infection of the central nervous system has. To do this, they used brain tissue from a person who had died of Covid-19, carried out animal experiments on mice and worked with brain cells in the laboratory that were supposed to mimic the three-dimensional structure of the brain. Other viruses, such as the Zika virus, are known to attack the brain as well. However, according to the study, the Sars-CoV‑2 behaves differently. Akiko Iwasaki, an immunologist at Yale University, speaks of a “silent infection” in the New York Times (NYT). The virus uses the brain cells to multiply, but does not destroy them. This means that the human organism’s immune response is also absent. The virus appears to soak up all of the oxygen near the infected cell and “starve” neighboring cells, so to speak.
On secret routes into the brain
It is still unclear how the virus even gets into the brain. Infections of the brain are rather rare, also because it is particularly protected by the blood-brain barrier. Because the nerve cells cannot be reproduced. “If the brain becomes infected, it can have fatal consequences,” says Iwasaki, who led the study. However, it appears that some people are prone to corona infection in the brain due to their genetic background, high viral load, or other reasons. It has long been suspected that Sars-CoV‑2, starting from the mucous membranes of the upper respiratory tract, attacks the olfactory nerve and from there reaches the brain. Penetration through the eyes or the bloodstream also appears possible. Alysson Muotri, a neuroscientist at the University of California at San Diego, who has also done research on the Zika virus, suspects that the coronavirus reduces the number of synapses, the connections between neurons. This effect is already visible days after the infection, Muotri told the NYT. The researchers assume that it is once again the ACE2 receptor that Sars-CoV‑2 serves as the portal of entry into the body. Although there is very little ACE2 in the brain, the virus has been shown to use this protein in other organs to penetrate.
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In addition, the scientists were able to show that a neuronal infection can be prevented: Either by blocking ACE2 with antibodies or by administering cerebrospinal fluid from a Covid-19 patient. Through the experiments with mice, the researchers come to the conclusion that a viral infection in the brain can be more deadly than an infection of the respiratory tract. If the mice had the infection in the brain, they died within six days; if the lung was infected, this was not the case. Doctors had repeatedly reported that severe illnesses resulted in increased levels of impaired consciousness, delirium or strokes. They are now considered an indicator of a poorer prognosis for Covid 19 patients.