A Comparison of Deformed Wing Virus in Deformed and Asymptomatic Honey Bees

Abstract

Deformed wing virus (DWV) in association with Varroa destructor is currently attributed to being responsible for colony collapse in the western honey bee (Apis mellifera). The appearance of deformed individuals within an infested colony has long been associated with colony losses. However, it is unknown why only a fraction of DWV positive bees develop deformed wings. This study concerns two small studies comparing deformed and non-deformed bees. In Brazil, asymptomatic bees (no wing deformity) that had been parasitised by Varroa as pupae had higher DWV loads than non-parasitised bees. However, we found no greater bilateral asymmetry in wing morphology due to DWV titres or parasitisation. As expected, using RT-qPCR, deformed bees were found to contain the highest viral loads. In a separate study, next generation sequencing (NGS) was applied to compare the entire DWV genomes from paired symptomatic and asymptomatic bees from three colonies on two different Hawaiian islands. This revealed no consistent differences between DWV genomes from deformed or asymptomatic bees, with the greatest variation seen between locations, not phenotypes. All samples, except one, were dominated by DWV type A. This small-scale study suggests that there is no unique genetic variant associated with wing deformity; but that many DWV variants have the potential to cause deformity.

In vivo evolution of viral virulence: switching of deformed wing virus between hosts results in virulence changes and sequence shifts

“…Hence, this phylogenetic analysis did not help to easily answer the question whether DWV‐A or DWV‐B is more virulent but rather suggested considerable virulence differences within DWV‐A and ‐B. This result is consistent with a recent study that did also not find consistent differences between the entire DWV genomes from crippled or asymptomatic bees (Brettell et al ., ). However, the cited study might also have suffered from the fact that it cannot be excluded that the analyzed asymptomatic bees also included bees which only looked healthy but were actually suffering from a DWV‐B infection of the brain, hence, carried the virulent DWV‐B variant.…”

The honeybee (Apis mellifera) developmental state shapes the genetic composition of the deformed wing virus-A quasispecies during serial transmission

“…Despite many decades of co-existence between honeybee, V. destructor and DWV, in millions of colonies and billions of honeybees world-wide, the pathology and virulence of DWV remain stubbornly linked to direct vectored transmission by V. destructor in developing pupae 14,[22][23][24][25]34 , with DWV pathology, virulence and titres all disappearing from honeybee colonies when varroa is removed 23,29 . This suggests that DWV genetic adaptation to transmission by V. destructor is either non-existent, and DWV virulence largely determined by the transmission route and viral titres 25 , or ephemeral; present only during varroa-mediated transmission with the DWV quasispecies rapidly returning to a default genetic shape and composition when varroa transmission is removed.…”

“…The principal varroa-transmitted virus is currently DWV 14 . There has long been a lively debate 19 as to whether the severe pathology caused by DWV is primarily due to genetic adaptation by the virus towards increased virulence [20][21][22] or due to excessive virus titres 17,[23][24][25] precipitated by this potent, novel transmission route [25][26][27][28] . Of course, these two alternatives are not mutually exclusive.…”

“…Of course, these two alternatives are not mutually exclusive. It has been conclusively shown that DWV is directly responsible for the deformed wing symptoms 25,29,30 ; that these symptoms are directly related to both the amount of virus and the transmission route 14,22,24,25 , and that the different major DWV variants (and especially their recombinants) have different replicative capacities in both honeybees and V. destructor 20,21,[31][32][33] , as well as different relationships with honeybee pathology at individual bee 24,34 and colony level 20,21,31,35 . What is less well known is how the virus adapts genetically during these transitions and transmissions.…”

Adaptation in Honey Bee (Apis mellifera) Colonies Exhibiting Tolerance to Varroa destructor in Ireland

“…Damage to idiosoma can be crushed/broken, while leg damage can vary from the removal of the tip or apoteles to multiple legs leaving empty sockets. (Brettell et al, 2017) concluded that a high DWV load was the only consistent factor associated with wing damage. This latter study also found that using RT-PCR, deformed bees contained the highest viral loads, which is consistent with the findings here.…”