Eric PyrrhusAug 27, 2023

1/9
Some people feel that SARS-CoV-2 infection of the brain is "rare". (e.g. <10% of cases)

But can we really say that #SARSCoV2 infection of the nervous system is rare? 🤔

That's a question posed by neuroscientist Yan-Chao Li of Jilin University in his literature review and meta-analysis:

"What can CSF testing & brain autopsies tell us about viral neuroinvasion of SARS-CoV-2?"
https://doi.org/10.1002/jmv.26943

👇 Thread below 👇

#virus #virology @virology #InfectiousDisease #coronavirus #covid

Show threadEric PyrrhusAug 27, 2023

2/9
Lead author Yan-Chao Li has spent the last 15 years studying coronavirus infections of the nervous system.

The authors point out that brain infections are extraordinarily difficult to detect at autopsy, partly due to the large, inhomogeneous nature of the brain tissue and the significant possibility of false negatives:

Show threadEric PyrrhusAug 27, 2023
3/9
Furthermore, the meta-analysis suggests that CSF testing may not be much help in detecting brain infection, again due to a possibly large number of false negatives:
Show threadEric PyrrhusAug 27, 2023
4/9
The review notes that one reason why it is so hard to determine which part of the brain to test at autopsy is the fact that brain infections don't necessarily come with histologically observable inflammation:
Show threadEric PyrrhusAug 27, 2023
5/9
And when there is observable inflammation, the authors note that observed brain infections might explain the observed brain inflammation better than any observed microvascular injury:
Show threadEric PyrrhusAug 27, 2023
6/9
Unfortunately, many autopsy studies appear to have simply chosen a few convenient parts of the brain to sample, increasing the likelihood of false negatives:
Show threadEric Pyrrhus
7/9
Therefore, the authors conclude that SARS-CoV-2 infection of the brain can not be assumed to be a rare occurrence:
Aug 27, 2023 at 7:13amWeb
Show threadEric PyrrhusAug 27, 2023

8/9
In addition, one more significant methodological problem has been raised by other authors.

Any viral RNA will rapidly degrade in any sample in a matter of hours, unless an RNA stabilizer is added to the sample right at time of sample collection - not at time of extraction:

Show threadEric PyrrhusAug 27, 2023

9/9
One autopsy study, performed by a group of NIH investigators, correctly treated their samples with an RNA stabilizer as soon after death as possible.

This study found much higher levels of viral RNA than studies that neglected to use any RNA stabilizer: