Hi all!
To my knowledge most (all?) organisms on this earth suffer from some pests - microriganisms (diseases), parasites etc. 
Thus I suppose that something somewere is feeding on varroa, infecting this mite. The fact that varroa jumped to another host (from A. cerana too A. mellifera) could mean that it left behind some of its problems of life.
So is there anyone out there searching for hyperparasites of varroa, viruses of Varroa, etc.
Let´s say (dreaming) that Varroa had a kind of mite sucking on it and that we could enhance it´s damage to Varroa by our management practice - nice thought :-)
I now it is difficault working with theese things (they are so small, living hidden etc), but there must be possabilities in this.
regards 
Morten Petersen
From Denmark, Europe (56 deg. N, costal climate)