Diversity in a honey bee pathogen: first report of a third master variant of the Deformed Wing Virus quasispecies

Mordecai, Gideon J; Wilfert, Lena; Martin, Stephen J; Jones, Ian M; Schroeder, Declan C

The global decline in honey bee populations over the past few decades has been attributed to the ectoparasitic mite Varroa destructor and its affiliation with Deformed Wing Virus (DWV) type A variant (Dainat et al., 2012; Martin et al., 2012; Schroeder and Martin, 2012; Francis et al., 2013) . The role of honey bees as pollinators is vital to the environment and economy, as bees are a key pollinator species for agriculture. The economic value of honey bees is estimated to be more than 225 billion US dollars worldwide (Gallai et al., 2009) . DWV, a member of the single-stranded positive-sense RNA genus Iflavirus (Lanzi et al, 2006) , exists as a group of closely related viruses, often considered as variants of the same species complex . The ICTV (The International Committee on Taxonomy of Viruses) database categorises DWV type A as two variants, DWV (Lanzi et al, 2006) and Kakugo virus (KV) (Fujiyuki et al., 2004) . A second closely related virus Varroa destructor virus-1 (VDV-1) is also part of the genus Iflavirus, which is now designated DWV type B Mordecai et al., 2016) . DWV type B was designated a separate species based on a nucleotide identity to DWV type A of ∼ 84% that, according to demarcation criteria, is sufficient dissimilarity to warrant the creation of a new master variant (Fauquet et al., 2005) . VDV-1 was originally isolated from V. destructor but has since been reported to replicate in honey bees (Ongus et al., 2004; Zioni et al., 2011) where it has been shown to cause wing deformities in bees (Zioni et al., 2011) . DWV type B was also recently found to dominate the DWV population in honey bees from an isolated apiary in Swindon, UK (Mordecai et al., 2016) ; to the apparent exclusion of any other master variants. In honey bee populations that have never been exposed to Varroa mites, DWV exists in a very large variant swarm with numerous master variants . However, transmission of DWV by Varroa reduces variant diversity to one master variant . Therefore, DWV exists as an endlessly mutating swarm of variants with these master variants constituting part of this quasispecies and sharing a recent common ancestor (Baker and Schroeder, 2008; Martin et al., 2012) . The dominance of one master variant over another will lead to ultimately different life histories for the colony, that is, death if DWV type A dominates or health if DWV type B dominates (Mordecai et al., 2016) .