Although the SARS-CoV-2 virus is primarily considered as the respiratory system, the damage caused by the pathogen did not spare the other organs in the body. Now, a new study by researchers from Columbia University’s Irving Medical Center reports that although the coronavirus does not directly infect the brain, it can still cause significant neurological damage.
According to the article, which is the largest published report containing COVID-19 brain autopsies involving more than 40 patients, there were no signs of the virus in the brain cells of the afflicted. However, it is likely that the inflammation caused by the virus in the blood vessels of the brain or other body parts can cause neurological changes in the brain.
“At the same time, we have observed many pathological changes in these brains, which may explain why seriously ill patients experience confusion and delirium and other serious neurological effects – and why those with mild cases may experience ‘brain fog’ for weeks and months,” said Dr. James E. Goldman, co-author of the study, said in a statement.
Autopsy of the brain
For the study, the authors examined the brains of 41 patients who lost their lives to COVID-19 while hospitalized. The patients were between 38 and 97 years old. Of these, almost half received intubation. All their lungs were damaged by the virus. The duration of hospitalization varied among these patients. While some died shortly thereafter after being brought to the emergency room, others remained in the hospital for several months.
Extensive laboratory and clinical examinations were performed on all the patients, and some underwent CT and MRI scans. Interestingly, several of the patients were of Spanish ethnicity. To identify the presence of the virus in the glial cells and neurons in the brain, the team used several methods. These include RT-PCR (a technique to detect viral RNA), RNA in situ hybridization (a method to detect viral RNA within intact cells) and test antibodies (for the detection of viral proteins within cells) .
No evidence of virus in brain
Despite extensive investigations, no evidence was found that the virus is present in the patients’ brain cells. While RT-PCR tests have detected trace levels of the coronavirus’ RNA, it could possibly be attributed to the virus found in the leptomeninges (two inner layers of tissue that cover the spinal cord and brain) or the blood vessels that surround the brain.
Regarding the comprehensive nature of the current study, dr. Goldman said: “Although there are some articles that claim to have found virus in neurons or glia, we think it is the result of contamination, and that any virus in the brain enters the blood vessels of the brain.”
Dr. Peter D. Canoll, co-author of the study, stressed that the low amounts of virus in the brain are not related to the abundance or spread of neuropathological observations. The team conducted tests on more than two dozen regions of the brain, including the major olfactory bulb.
These areas have been investigated based on speculation in other studies that the virus can infect the brain from the nasal cavity by using the olfactory nerve. “Even there, we found no viral proteins or RNA. Although we found viral RNA, and proteins in the patients’ nasal mucosa and in the olfactory mucosa high in the nasal cavity,” said Dr. Goldman noted.
Damage to oxygen
The brain pathology among the examined patients was divided into two categories. The first group were those whose brains suffered damage due to oxygen or hypoxic damage. “They all had serious lung diseases, so it is not surprising that there is hypoxic damage in the brain,” said Dr. Goldman explains.
In some cases, the damage – caused by strokes – stretched over large areas. However, most of the damaged areas were very small and were only observable under a microscope. Compared to other features, the researchers suggested that hypoxic damage is caused by blood clots that cause these small areas to be temporarily stopped.
Indications of neural death
The second group of patients consists of those who show signs of damage to the neurons. The researchers discovered that a large number of microglia were activated in their brains and attacked neurons through a process called neuronophagy.
Microglia are immune cells found in the brain that are activated by pathogens. The activated microglia are mostly found in the lower brainstem (associated with heartbeat and consciousness) and hippocampus (involved in mood and memory).
The team is now conducting autopsies on COVID-19 survivors who died a few months after recovering. “We know that microglia activity will lead to loss of neurons, and that the loss is permanent. Is there enough loss of neurons in the hippocampus to cause memory problems? Or in other parts of the brain that help draw our attention? “It’s possible, but we really do not know at this stage,” concluded Dr. Goldman.