I have been reading papers and taking notes on one virus in this family for over 3 years.  Initially what drew me to it was that it was, for a while at least, associated with aggressiveness in honey bees, but that “for a while at least” was always kind of problematic for me.  Lately I have fallen back into the DWV-rabbit hole and finally see a story that involves a disappearing (maybe) honey bee virus from Egypt, the spread of parasitic bee mite due to post World War II Green Revolution efforts to spread bee keeping to Asia, honey bee colony collapse, cognitive impairment of honey bees by viruses and a woman who received her PhD in Nuclear Physics in 1937 and ends up forming a international charity to study bees after receiving a bee hive as a wedding gift.  And angry agressive bees.  Maybe.   But first, some basic information about these three viruses.

image from Martin & Brettell, 2019

Deformed Wing Viruses A, B & C (DWV-A, -B, -C)  belong to the Order Picornavirales (1), which they share with Polioviruses and Rhinoviruses (which cause a good number of cases of the common cold). I get so bored with human viruses (that’s the original reason I started doing this, virology is so much more interesting when you move away from humans), so let’s move quickly to the fact that they are in a different Family, the Iflaviridae.  There are some general features that they share with other members of the Order, like not having a lipid envelope around the protein virion shell, having a genome comprised of a single strand of RNA that is able to immediately be translated into protein by ribosomes (“(+)-stranded”) and that the viral proteins are encoded by one large open reading frame (one AUG start codon for all of them) with the individual proteins being cut out of that larger polyprotein by a viral protease.  The Iflaviruses (there are more than just the DWVs in this Family) have a ~8,800 to 9,7000 nucleotide long genome, depending on which specific virus you are talking about.

This group of viruses are mostly known for infecting one species of bee, the European honey bee – Apis mellifera, but a honey bee mite with the wonderful name Verroa destructor is important in spreading them to uninfected bees.  The fact that they are known mostly for infecting Apis mellifera probably has more to do with the agricultural importance of this bee than it does with a real preference (tropism) for it.  One excellent review (2) puts the number of arthropod species that harbor DWVs at 64 – including one arachnid!  You have to be really careful with information like that though because if one of those studies was crushing up the entire insect or spider – including its gut contents – that virus could be coming from a bee (or other insect) in the gut.  If you crushed up a whole human and looked for viruses, you would find many many more bacterial and plant viruses in that human (assuming they ate vegetables) than any human virus.  I have not read the studies that address the 64 species that DWVs have been associated with though.  Let’s bee charitable and assume the researchers carefully removed the guts first.

As with many RNA viruses, DWV-A, -B & -C exist as pools of very closely related but not identical viruses; to give you a flavor for their relationships – they are anywhere from  79-84% identical at the nucleotide level (depending on which two you are comparing) but 89-95% identical at the amino acid level (2).  A & B are more closely related to each other than to C; recombinant A/B viruses have been recovered in the wild but don’t appear to out-compete either of their parents.  To give you a sense for prevalence, one group of researchers found DWV-B in 3% of bee colonies in 2010, but that increased to 65% in 2016.  I am relying on the Martin & Brettell review for that information and have not read the studies myself, so there might be some caveats to that.  Putting together a bunch of individual studies, roughly 55% of colonies worldwide are infected (2), but I took a brief peak at one of those studies from Austria and found that they tested 131 honey bees from all over Austria and 91% of them were DWV+ (3).  I’m curious if any of these studies figured out the prevalence within single hives, surely they must, but multiple studies remark on observations that hives can harbor very low level infections with fewer bees infected. 

Lumping them together as a group, their effect on bees is variable and  appears to depend at least in part on the presence of Verroa destructor but range from decreased adult lifespan to premature foraging and cognitive difficulties to deformed wings.  (And agressive anger.  Maybe.)  Not all bees are affected in the same way and it certainly is not clear that DWV is responsible for colony collapse disorder, at least not on its own. 

References:

(1) “Iflavirus”, ViralZone https://viralzone.expasy.org/278?outline=all_by_species. for all taxonomic, genomic and virion structural information on viruses, I tend to use ViralZone

(2) Martin & Brettell 2019. Annual Review of Virology.  Deformed Wing Virus in Honeybees and Other Insects

(3) Berenyi, O et al 2006 Applied & Environmental Microbiology. Occurrence of six honeybee viruses in diseased Austrian apiaries