> Once the bees get the virus, they can spread it without any additional

> assist from the mites.  It is not the exponential increase in mites
but 
> the increased spread of virus. So you can have high mite loads but no 
> major losses (look at parts of Canada), or low mite loads (usually
after 
> treatment) with major loss (look at US commercial operations ).

Who told you that?

Here's two things that may change the way you look at
bee viruses spread within a colony.

First, colonies that look fine tends to carry low virus levels.  These
"inapparent infections" are seemingly universal.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=535170

Second, there is a direct, and compelling correlation between
the number of mites in a cell at the same time, each trying
to reproduce, and the number of viruses transmitted between
the bee pupae and the mites.

Judy Chen showed this clearly in her work where she looked
at specific viruses in individual bees and individual mites
added by hand to individual cells.  (I don't have a handy
copy to verify, but I think that the paper with this data
was "Horizontal and vertical transmission of viruses in the 
honey bee, Apis mellifera" (Judy Chen, Jay Evans, Mark Feldlaufer)
in the "Journal of Invertebrate Pathology".

Her work showed clearly that mites became unwitting virus
carriers only after feeding on bees, and that with more 
mites per cell, the odds of the bee pupae and the mites
transmitting one or more viruses between them went up in
direct correlation with the number of mites per cell.

So it is exactly "the exponential increase in mites" that 
CAUSES "the increased spread of virus".

So, we have firm evidence that:

a) Bees can not just tolerate, but thrive while carrying
   viruses among their population, and that these viruses
   remain at low levels, remain "undetectable" in terms
   of overt symptoms.

b) That these viruses are NOT transmitted within the
   colony at any sort of rate that would be called
   an "increased spread of virus" by the bees themselves
   without a significant varroa load.

c) That once one has a significant varroa load, one
   DOES get an "increased spread of virus" .

Mites certainly can and do show up on a drifting forager 
carrying multiple viruses, but the mite picked up all 
these viruses from bees in a hive with a high varroa 
load, and hence, multiple viruses at high levels.

If, as you claimed, bees could "spread it [a virus] without 
any additional assist from the mites", then hives would
be dying with things like DWV and ABPV at random, 
regardless of mite level, which does not happen.

If, as you claimed, bees could spread any of these
bee viruses, they would be spread more in late
spring and early summer, when bee populations peak. 
Late summer and fall is when one can use casual 
naked-eye inspections to detect things like DWV,
which also underscores varroa's role in spreading
the viruses, as this is when varroa populations
peak.

So, while you are correct when you said "Varroa is not 
the problem. It is the virus.", the lack of a set of
anti-viral tools forces us to focus on the mite
end of the problem.

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