Although the primary target of the SARS-CoV-2 virus is said to be the respiratory system, the damage caused by the pathogen did not spare the other organs of the body. Now, a new study by researchers at Columbia University, Irving Medical Center, has reported that although coronavirus does not infect the brain directly, it can cause considerable neurological damage.
According to the paper, which is the largest published report detailing COVID-19 brain autopsies involving more than 40 patients, there were no signs of the virus in the brain cells of those affected. However, it is likely that inflammation triggered by the virus in the blood vessels of the brain or other parts of the body can cause neurological changes in the brain.
“At the same time, we observed many pathological changes in these brains, which could explain why seriously ill patients have confusion and delirium and other serious neurological effects – and why those with mild cases may experience ‘brain fog’ for weeks and Monday, “said Dr. James E. Goldman, co-author of the study, in a statement.
Brain autopsy
For the study, the brains of 41 patients who lost their lives to COVID-19 while hospitalized were examined by the authors. Patients ranged in age from 38 to 97 years. Of these, almost half received intubation. All their lungs had been damaged by the virus. The duration of hospitalization was varied among these patients. While some gave up shortly after being brought to the emergency room, others remained in hospital for several months.
Comprehensive laboratory and clinical investigations were performed in all patients, some of whom underwent CT and MRI scans. Interestingly, most of the patients were Hispanic. To identify the presence of the virus in glia cells and brain neurons, the team used several methods. These include RT-PCR (a technique for detecting viral RNA), in situ RNA hybridization (a method for detecting viral RNA inside intact cells) and antibody testing (for detecting viral proteins inside cells).
There is no evidence of a virus in the brain
Despite extensive examinations, no evidence was found of the virus in the patients’ brain cells. While RT-PCR tests have detected traces of coronavirus RNA, it can be attributed to the virus present in the leptomeninges (two inner layers of tissue that cover the spinal cord and brain) or the blood vessels around the brain.
Speaking about the comprehensive nature of the current study, Dr. Goldman noted: “Although there is some evidence that they found the virus in neurons or glia, we believe it results from contamination and any virus in the brain is contained in the blood vessels of the brain.” .
Dr. Peter D. Canoll, co-author of the study, pointed out that small amounts of the virus in the brain are not correlated with the abundance or distribution of neuropathological observations. The team performed 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 brain the nasal cavity using the olfactory nerve. “Even there, we did not find viral proteins or RNAs. Although we did find viral RNAs and proteins in the nasal mucosa of patients and in the elevated olfactory mucosa in the nasal cavity,” Dr. Goldman noted.
Oxygen-free damage
Brain pathology among the examined patients was divided into two categories. The first group was the one whose brain suffered damage due to lack of oxygen or hypoxic damage. “Everyone had severe lung disease, so it’s not surprising that there is hypoxic damage to the brain,” said Dr. Goldman.
In some cases, the damage – which was caused by strokes – spread over large areas. Most damaged areas, however, were very few and were only detectable under a microscope. Comparing it with other features, the researchers suggested that the causes of hypoxic damage to these small areas were brought on the blood clots that caused a temporary shutdown of the oxygen supply to these areas.
Indications of neuronal death
The second group of patients consisted of those who showed signs of neuronal damage. Making an unexpected discovery, the researchers found that a large number of microglia were activated in their brains and attacked neurons through a process known as neuronophagy.
Microglia are immune cells found in the brain that are activated by pathogens. Activated microglia were found mainly in the lower brainstem (associated with heartbeat and consciousness) and in the hippocampus (involved in mood and memory).
The team is now conducting autopsies on COVID-19 survivors who died months after recovery. “We know that the activity of the microglia will lead to the 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 direct our attention? It is possible, but we really do not know at this time “, concluded Dr. Goldman.