Alter's viruses are 'Polytropic MLV-related viruses', and so he could have named them 'PMRV' (instead of XMRV). He hasn't named them PMRV, yet. Instead, he refers to them as Polytropic MLV-related viruses, or just MLV-related viruses.

All of the viruses found so far in the two papers, are MLV-related viruses, and they are Human Gamma Retroviruses (HGRV's), which is an umbrella term.
•'Xenotropic' means that a virus cannot infect, or replicate in, its original host species (i.e. mice), but it can jump to another species (i.e. humans) where it can become a whole, complete, replicating virus.

•'Polytropic' means that a virus can infect both its original host species (i.e. mice) and it can jump to another species (i.e. humans).

The difference in the meaning of the two terms is why the new viruses that Alter has detected cannot be called XMRV. Alter's viruses are related to Polytropic MLV's, not Xenotropic MLV's.

Read more

På norsk med Google Translate