Possible that prednisone can increase viral replication. However, prednisone is immunosupressive so seperating out the induction of viral replication by prednisone as oppesed to immunesupressive effects would be difficult.
Good point about prednisolone being imunosuppressive, but XMRV also has a Glucocorticoid response element in the U3 region, so glucocorticoids should also increase viral replication directly.