There are two ways to prove causality if you think about it.
1) Give XMRV+ ME/CFS patients Anti-Retrovirals and see if they get better, en mass.
2) Find a unique immune abnormality only people with ME/CFS have, who are XMRV+
(Like CD4 in HIV). Possibly it could be NKC/Cytokine/Chemokines? Maybe T-Cell/B-Cells are infected with XMRV, 'disabling' their function? Or a combination...
If we are very lucky we'll do 2) then go to 1) It's a fantasy but not impossible. All that is needed is an agreement and more testing. Nancy Klimas had said for years cytokines could be a bio-marker, but that would need to be tied in with being XMRV+.
If all her ME/CFS patients with wonky cytokines all universally have XMRV infection then we're onto something. I'm sure Nancy and Dr Mikovits are up to discussion behind the scenes, surely? Lets see what's revealed by the end of the year.
I wonder what Dr De Meirleir means by an AIDS like signature?..perhaps that's a give away that we could be going down the T-Cell/B-Cell/NKC route. XMRV is bad enough, now scientists have to show just what XMRV does to people who have diseases, starting with ME/CFS. What is the unique feature we all share when infected with XMRV, that leads us to develop a state of, ME/CFS?