Hi MayB, and welcome!
Parvovirus B19 is not a virus form that is named in connection with FM nowadays. EBV is named more often (causing 'mono').
There are 9 studies on pubmed trying to find the B19 connection, several in the 1990s & several in the 2000s.
The results point if at all more to a feeling that virus infections may for some be a trigger for FM.
As someone who feels his FM might have been triggered by swine flu (and 'researches' a lot), I'd say:
It will be hard and take a long time to prove if these really are triggers. If at all it will then maybe depend on FM-subgroups that may be found, also difficult to prove. And it doesn't help. Same as trauma as a possible trigger for some. For some it may help cope a bit to be able to blame it on "something" and not ourselves. It's good to try to treat our immune seeming problems with anti-immune supps like our mental problems (e.g. PTSD) with psychotherapy (e.g. trauma therapy), but that will not cure FM, it may just alleviate part of it or make our lives easier. And it doesn't depend on the medical proof of a trigger.
Yesterday, I phoned with the doc who'd unsuccessfully done ozone injections on me a year ago about how to praps get the bills paid for by insurance. When I told him I'm suffering long term from severe jab side effects, he 'knowingly' answered: "yes, you know there were always coronaviruses before COVID 19 [as if we didn't know], and we are now seeing these side effects in people who had these; you may want to come and do another stint of treatment here." Well I didn't laugh in his ear, but how sweetly naive this is: We probably all had these coronaviruses, there is no proof in hindsight that we did or not, nor that this really is the trigger. He'd also obviously forgotten that his treatments didn't help me at all, neither ozone nor acupuncture, and that he'd seen me off with general platitudes that I've always been doing diligently anyway... But a very kind old guy, meaning well.