As soon as the WPI found XMRV I realized that it had to be transmitted more easily than HIV. Otherwise you wouldn't get the outbreaks they've had. I think Cheney is probably right on this one. I feeling is that it is probably transmitted in the same way as Glandular fever (Mono), so that would include saliva. I think that nasal secretions would be likely as well.
p.s. Think I may have just found Cheney's explanation: "Over time, the infections of various organs tended to be cleared by either immune mechanisms but especially by restriction enzyme systems present in almost all human cells that hypermutate the virus so it cannot persist as a competent infectious agent. Indeed, mutated viral strains are almost always found in CFS cases by both Judy Mikovits at WPI and Frank Ruscetti at NCI. Sometimes this makes the virus incompetent as an infectious agent and sometimes has no effect on infectiousness."