A new analysis of the widespread deformed wing virus (DWV) in honey bees shows that the virus has gone from an endemic to a global epidemic because of greater movement of a major vector, the Varroa mite.
The mite has spread in large part due to human trade of the bee colonies it infests.
The study published in the journal Science adds to scientists’ understanding of the globally pressing issue of pollinator health by describing the worldwide transmission routes and dynamics of DWV based on analysis of a new and large molecular data set.
Previous evidence indicates that the presence of the mite Varroa increases the spread of DWV across honey bee populations, not only by acting as a vector but also by increasing the virulence of the virus.
While scientists have a grasp on how Varroa affects DWV spread at the individual and colony level, its importance to the global spread of DWV is less well understood; some scientists think the mite became an important factor when it expanded from its native host, the Asian honey bee, to the European honey bee – then going on to cause an epidemic of DWV.
Others think DWV was native in the European honey bee but reemerged because of the mite’s increasing presence.
Here, to better understand how the Varroa mite has impacted global DWV spread, Lena Wilfert of the University of Exeter in the United Kingdom and colleagues used molecular sequencing of the virus and mites from 32 locations in 17 countries.
Wilfert worked with researchers from the University of Sheffield in the UK; ETH Zürich in Zürich, Switzerland, University of Cambridge in the UK; University of Salford in Manchester, UK; and University of California, Berkeley.
They estimated the major routes of the virus’s spread by comparing geographic and host-specific patterns.
Their results lend support to the idea that DWV is an endemic honey bee pathogen of the European honey bee that has recently re-emerged through the spread of Varroa as a vector.
The authors say that to reduce the negative effects of DWV on pollinators, tighter controls, such as mandatory health screenings and regulated movement of honey bees across borders, should be imposed.