The researchers found the infection in the brain of a person who died from COVID-19, in the central nervous system of laboratory mice infected with the coronavirus, and in organoids – three-dimensional cultures of neurons that mimic the brain.
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Unlike other pathogens, such as the Zika virus, the coronavirus causes a silent infection that does not provoke an immune response that clears infected cells from the brain tissue. Instead, SARS-CoV-2 restricts neurons’ access to oxygen, which contributes to their death. It also rapidly reduces the number of synapses – connections between nerve cells – harming cognitive performance.
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The virus enters brain cells through the ACE2 receptor located on the surface of the cell membrane. This receptor is mainly expressed in lung cells, which explains why coronavirus often causes pneumonia.
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However, scientists have found that a small amount of ACE2 in the brain still allows SARS-CoV-2 to penetrate into nerve tissues and cause pathological changes.
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However, it is not yet clear how the virus could enter the brain. It is believed that it can do this through the olfactory bulb, eyes, or even the bloodstream.
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