Long COVID and Neurogenesis

This is an impotant article regarding neuropsychiatric sequelle of COVID19, the most important symptoms of long COVID. 

SARS CoV2, the pathogen of COVID19, disrupts the blood brain barrier. Then inflammatory cytokines cause inflammatory lesions at various sites of CNS. One of the targets is the neuronal stem cell at the hippocampus. It is the stem cell destined to differentiate to neuron; that is, the process of neurogenesis. This seems to be the pathogenesis of neuropsychiatric symptoms long lasting after the acute infection. 

The symptoms caused by this mechanism are typically cognitive dysfunction and depressive disorder. For elderly, it might be a predisposing factor for dementia.  

https://academic.oup.com/brain/advance-article/doi/10.1093/brain/awac270/6672950

In our country, the long COVID is not well recognized yet even though it occurs in 10 to 30% of cases. The epidemiological data in the US and the UK tell that 1 to 2 % of all workers could not go on working due to the long COVID. I suspect our government intentionally ignores of that sequelle which could be a serious problem for the patient as well as for the burden to social security in the future.

At present, Omicron variants seem to overwhelm in the Eastern Asia area like Japan, Korea or Taiwan while they are not so ominous in the Western countries. Most of the cases are mild and the fatality rate is not very high. But with its dramatically high infectiousness, the surge could be really big and could cause collapse of medical system as we have experienced for the past few months. This could be explained with immunogenetic standpoint of view. It reminded me of the drastic epidemic in the Western counries at the beginning of this pandemic while it was of limited range and severity in the Eastern Asia. No one knows there could be another surge with a new variant with different infectiousness and immunological evasiveness.  

One more personal impression on this issue. When I was a student, we were taught the neuronal tissue won't be regenerated or even newly generated in adulthood. Since 1990s, it seems the concept of stem cell, that is, neurogenesis, was applied to certain phenomenon as that in the hippocampus. In animal model, it was observed in olfactory system. Reading the paper quoted above, I was even moved to know the stem cell system works in adulthood brain. When I was working as a resident, the stem cell concept was found in differentiation of blood precursor cells. That neurogenesis is involved in memory function. Cognitive disorders could be elucidated as the disorder of this neurogenesis, if not all. I am sure researchers must be excited at this perspective open to them now. 

My own neurogenesis is being deteriorated year by year. But I should stir the neuronal stem cell to follow such exciting new knowledge.