Don't know enough about biology to determine if this hypothesis makes sense or not, but here are my attempts to understand what's in the paper.
It seems like Prusy's team was doing research into HHV-6. Their experiments suggested that HHV-6 reactivation not only induces changes in the immune function but also some changes in mitochondrial function.
Old (but unconfirmed) ME/CFS research suggested a connection with HHV-6 (the person who co-discovered HHV-6, Dharam Ablashi, also became co-founder of what is now the IACFS/ME) and some of the key HHV-6 abnormalities found in mitochondrial metabolism such as pyruvate dehydrogenase were also mentioned in ME/CFS research. I think that sparked the interest of the group to look at ME/CFS and how HHV-6 might be relevant there. They write:
"our in vitro HHV-6A reactivation studies pointed toward potential similarities between viral reactivation and ME/CFS pathophysiology."
So they looked at HHV-6 in the blood, isolated cells, serum, and hair follicles of 25 ME/CFS patients and 10 controls. Unfortunately, they couldn't find much. The paper writes that
"low copies of virus DNA and RNA in blood of ME/CFS patients created a confusing scenario."
But there was one other option the researchers were thinking of. Their experiments suggested that fluid from HHV-6A–reactivated cells cause similar changes in the mitochondrial architecture of nearby non-infected cells. That suggested a transferrable factor coming from HHV-6A– reactivated cells that can induce those abnormalities in other cells.
They thought that maybe something like this was happening in ME/CFS. Maybe some difficult to trace part of the body is infected and sending this factor to the rest of the body. The authors write:
"A plausible explanation can be localized viral infection/activation in distant parts of the body, thereby releasing a few infected cells carrying activated virus or releasing some of the activation-mediated cellular factors into the blood stream."
That's when they started to test whether serum from ME/CFS patients also causes the changes induced by HHV-6A– reactivated cells. And this seemed to be the case. The paper reports:
"we showed that serum from ME/ CFS patients contained an activity that produced mitochondrial fragmentation, decreased mitochondrial ATP production, and induced a powerful antiviral state."
Those were the results Prusty mentioned at the NIH conference. Unfortunately, this paper provides little data to support this. It mostly seems to describe their way of thinking and some preliminary experiments. I suspect that's why Jonathan wasn't very excited. What we would like to see is a proper test of whether ME/CFS serum really induces those abnormalities.
I see this as a hypothesis paper - hopefully a proper test with more data will follow.