HSV, VZV, HIV, CMV, Zika, and Ebola are all viruses that are known to potentially damage blood vessels in the brain. I don't think it's correct to assume a virus cannot just by nature of being a virus.

>I doubt a virus can damage blood vessels in the brain.

An autoimmune response of the body is capable of damaging everything in the body. A pathogen is able to trigger any immune response in the body depending on what it is.

I don't know how your reasoning works but I can't follow it.