On the basis that I don't believe in spirits and such,
the only two options I would consider, because "spirit activity" cannot really be investigated, are "mind control", and disease.
Not to say, that I rule out the third option.
Like I said, there's nothing out there that can support it.
Scientifically speaking.
I'm no statistician, and I don't keep up with the medical journals.
I also have no connection to military, or special forces arm of any government.
From this point I will refer to "mind control" projects, as "Human driven disorders", and to "disease" as "Nature driven disorders".
Similarly, as you could say birth defects related to Agent Orange are "Human driven disorders", and let's say infections with naturally occurring pathogens would be a "Nature driven disorder".

We would have to look at the statistics,
how much correlation between infection and PANDAS in general population, in specific populations, in specific regions.
Does the quality of healthcare for a certain population influence the correlation.
Do PANDAS is endemic to certain country, region, ethnic group.
Can symptoms be reproduced in vertebrae animals using chemical agents, and different pathogens.
I don't know if any study like that exists.
I know nothing about PANDAS and whether it's a real thing to begin with,
Human driven or Nature driven.
The problem of misdiagnosis is always an all-present issue.
Facts don't care for consensus, and I would hate if we collectively decided that we're going to treat people with real pharmacology for made up disorder.
For years we've been over-prescribing medication for ADD/ADHD, when it may very well be a kin to giving drugs to people with different eye colour than our own.
When I wend through puberty I had "thoughts" that almost weren't my own. I was taught that children in puberty, especially boys, for a period of time lose all their empathy, just to magically regain it few years later.
Did I have PANDAS because of my thoughts of murder, rape and torture that went away after I was 16 years of age?
Hey, I had a lung infection at the age of 6 so it must be PANDAS, right?

Anyway, to finish the ramble.

I don't know the answer.
If i were to put my money where my mouth is I would probably say it's some disease.
Studies show that people who go through toxoplasmosis do engage in more risky behaviors on average.
Could very well be the case it's just an infection.