From what I have read, DWV is not a new disease, but mites have amped up the virulence of it and when it is present in the colony more of the bees are affected because the mites' bites allow it to be directly injected into the bees' circulatory systems.
The mites don't cause the disease they merely vector it much more efficiently.
The virus, absent the mites, was probably held more in check because it couldn't affect as many individuals in the colony. (Makes sense - if a disease kills all its hosts, it quickly dies out itself.)
The epidemiology of DWV is the #1 item on my winter study list.
It turns out there are (at least) two strains of DWV and infection with one (the less virulent strain) seems to afford protection from the other, more lethal one. A question I have is whether the less-virulent strain causes the characteristic deformed wing syndrome since that by itself is individually lethal to the affected bee. If it doesn't cause the deformity (which removes the infected bee from the colony) is it actually "deformed wing virus" or some other closely related virus? Do the bees chase infected-but-not-visibly-deformed bees out? Or do the infected bees stay in the colony, perhaps passing it the virus on?
As a general rule bees only can "bring the virus under control" (your term) by ejecting the infected bees, something beekeepers observe happening because of the visible deformity.
The "less lethal strain", if it causes the damaged wings to infected bees is still lethal to those individuals.
Either way I hate DWV and it spurs me on in my mite control efforts.
Enj.
