I don't know whether this has been posted earlier, here is the link: http://www.retrovirology.com/content/7/1/63 What catched my attention is this: "(...) XMRV displays more than 90% sequence identity with MLV and harbors distinct amino acid substitutions and a short deletion in the gag leader region. Strikingly, these combined features lead to a putative absence of glycoGag, an alternative open reading frame of the gag gene that has been shown to play a role in MLV replication and pathogenesis..." If I understand this correctly, replication and disease making genes are missing in this virus. On the other hand, we know that gammaretroviruses are used for gene therapy. Could it be that this virus is a lab accident, and found it's way somehow into humans ? Another virus-family, the lentiviruses, of which HIV is the most well known one, also integrate easily into human gnome. Could it be ... ? OS.