The Human Isolate Question-The WPI appears to propose that their use of a human isolate of XMRV allowed them to find an XMRV-like family of viruses containing VP62 strains, p variants of the virus (Lo et. als pMLVs) and other strains and that Dr. Singhs use of an XMRV clone developed from the VP62 strain lead her to miss those strains and that is one reason that she didnt find anything. (Note though that the WPI did say that the patients they directed to Dr. Singh tested positive for antibodies to the VP62 strain - which, given the increased sensitivity of Dr. Singhs tests she should have been more effective at picking up.The WPIs argument regarding using a human isolate possibly explain reduced results but its hard to understand how it could explain zero results. The data from the original study indicated that tests using VP62 were adequate to pick the type of XMRV found in that study. ).