>I'm genuinely curious- are there published studies showing that
mite-vectored DWV-A presents clinical symptoms?
i'm curious too, and don't have a dog in the fight. Dr. Genersch states
repeatedly in her recent paper that the degree of pathogenicity of the two
variants is "controversial"-- an understatement.
Take a look at:
The Two Prevalent Genotypes of an Emerging Infectious Disease, Deformed
Wing Virus, Cause Equally Low Pupal Mortality and Equally High Wing
Deformities in Host Honey Bees
The Two Prevalent Genotypes of an Emerging Infectious Disease, Deformed
Wing Virus, Cause Equally Low Pupal Mortality and Equally High Wing
Deformities in Host Honey Bees - PMC (nih.gov)
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6409761/>
It appears that DWV-A first established in the U.S., with a more recent
invasion by DWV-B. Unfortunately, with PCR, until one figures out the
right primers for identification, there will be questions. Keville
published three primers (which due to DWV acting as a quasispecies, may
also be controversial).
ABC Assay: Method Development and Application to Quantify the Role of Three
DWV Master Variants in Overwinter Colony Losses of European Honey Bees. ABC
Assay: Method Development and Application to Quantify the Role of Three DWV
Master Variants in Overwinter Colony Losses of European Honey Bees - PMC
(nih.gov) <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5707521/>
Their findings indicate that DWV-A could be deadly: "The ABC assay was used
on archived material from a Devon overwintering colony loss (OCL) 2006–2007
study; further implicating DWV type A and, for the first time, possibly C
in the untimely collapse of honey bee colonies. Moreover, in this study DWV
type B was not associated with OCL."
So how about the prevalence of the two variants, and their effects upon
colony losses?
Deformed wing virus variant shift from 2010 to 2016 in managed and feral UK
honey bee colonies.
Deformed wing virus variant shift from 2010 to 2016 in managed and feral UK
honey bee colonies - PubMed (nih.gov)
<https://pubmed.ncbi.nlm.nih.gov/34275024/>
"The ability of DWV-B to replicate to higher loads than DWV-A provides a
possible evolutionary advantage over DWV-A and may be an example of viral
attenuation, since longer-term trends indicate Varroa-virus-associated
overwintering losses may be declining. Furthermore, evidence suggests that
DWV-B is able to replicate in Varroa mites, while DWV-A cannot, and this
may play a role in the increased prevalence of DWV-B in colonies. In the
currently DWV-A-dominated USA, the rate of decline is periodically higher
than in other temperate regions [45]. Therefore, it is expected that, over
time, DWV-A would lose dominance in honey bee populations, as evidenced
here within. It is expected that colonies in the USA will eventually also
switch to DWV-B dominance. Since DWV-A was not completely eradicated from
the English honey bee colonies sampled, a re-emergence of DWV-A may occur,
highlighting the need for long-term landscape level monitoring over time."
The above appears to be in progress"
Recent spread of Varroa destructor virus-1, a honey bee pathogen, in the
United States Recent spread of Varroa destructor virus-1, a honey bee
pathogen, in the United States (nih.gov)
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5727227/pdf/41598_2017_Article_17802.pdf>
DWV-A Lethal to Honey Bees (Apis mellifera): a Colony Level Survey of DWV
Variants (A, B, and C) in England, Wales, and 32 States across the US.
Viruses-Basel. 2019 doi: 10.3390/v11050426.
We know that DWV was killing colonies in the U.S. by the late 1990s.
Martin and Keville, citing lower rates of loss in the U.K., suggest that
DWV-B is LESS, rather than more, virulent.
I'd sure like to see an analysis of archived bee samples from the U.S. from
back in the late 1990s through our massive colony losses in the early 2000s.
Randy Oliver
Grass Valley, CA
530 277 4450
ScientificBeekeeping.com
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