when they use the word contminant what they have done is redefined the word contaminant to suit themselves.
What they actually mean is a recombinant.They wont use that word because when mouse ervs recombine to produce vilable reproducible viruses then they are invariably highly pathogenic and usually also have the ability to infect other species.
They use their own definition of contaminant so that they can always say that they meant recombinant all along
This is the behaviour of shyster lawyers and not scientists.So when papers talk about a human gamma retrovirus being a "contaminant" be aware that they are not using the word in its normal scientific context.
The lay press of course will think that it is truly a contaminant. this imo is quite deliberate.
So i urge everyone not to take these terms at face value and when they are used press for a definition.
See also: CDC will now look for XMRV and MLV in their own lab workers ! or Bizarre CROI Conference suggests that XMRV is contamination and then they all run off to check if they are XMRV positive !!