RNA viruses have a mutation rate nearly a million-fold higher than their eukaryotic hosts. This generates a population of related viruses of high variation around one or more ‘master genotypes’ — known as a quasi-species swarm. The degree of nucleotide identity that defines a new viral variant or strain varies by virus, and is not clearly defined for many honey bee viruses. 

For example, Lake Sinai virus sequences in the NCBI database range in sequence identity from 69 to 99% at the nucleotide level, whereas proposed DWV master variants range from 79 to 84% identity at the nucleotide level, with up to 98.2% identity among sequences identified as DWV-A. A master variant or master type is the genotype with maximal fitness. Recent analysis has suggested the possible existence of three DWV master variants.

In a recent UK-based study, DWV-B genome equivalents and prevalence over time positively correlated with colony mortality, whereas DWV-A was not detected. However, statistical models suggest the association between DWV-B and Varroa may be more critical for honey bee health than either alone. This is important because it restates the difficulty of disentangling the close association of DWV with Varroa and their contribution to individual bee and colony mortality.

from
McMenamin, Alexander J., and Michelle L. Flenniken. "Recently identified bee viruses and their impact on bee pollinators." Current Opinion in Insect Science (2018).

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