Re neurodegenerative disorders, you might try Lyme disease. It passes the brain border, too and is misdiagnosed as anything from RA, to MS, to psych disorders as patients are passed along from doc to doc. No cures unless it is caught early on and only regressions until it hits again. Oh, and many think it was a bio weapon that escaped a lab in the US. A most interesting disease.
I agree with you Lyme disease and all neurodegenerative disorders are very bad. Though there is no evidence other then fake reports that claim Covid will form into a neurodegenerative disorder