Highly contagious honey bee virus transmitted by mites

This association is now thought to contribute to the world-wide spread and probable death of millions of honey bee colonies. The current monetary value of honey bees as commercial pollinators in the United States alone is estimated at about $15-$20 billion annually

The research conducted in Hawaii by researchers at Sheffield University, the Marine Biological Association, FERA and University of Hawaii, and reported in the journal Science (8 June 2012), showed how Varroa caused DWV – a known viral pathogen – to increase its frequency among honey bee colonies from 10% to 100%.

This change was accompanied by a million-fold increase in the number of virus particles infecting each honey bee and a massive reduction in viral strain diversity leading to the emergence of a single 'virulent' DWV strain.

As the mite and new virulent strain of virus becomes established across the Hawaiian islands the new emerging viral landscape will mirror that found across the rest of the world where Varroa is now established.

This ability of a mite to permanently alter the honey bee viral landscape may by a key factor in the recent colony collapse disorder (CCD) and over-wintering colony losses (OCL) as the virulent pathogen strain remains even after the mites are removed.

Notes for editors

Honey bee populations can experience spectacular crashes. The most recent being the well publicized colony collapse disorder (CCD), but its cause remains a mystery.

Varroa is a large mite (~1.5mm x1mm) that lives on the surface of honeybees, feeding off their blood and reproducing on their developing brood.

The arrival and spread of Varroa across the Hawaiian Islands offered a unique opportunity during 2009 and 2010 to track the evolutionary change in the honey bee virus landscape.

The mite facilitates the spread of viruses by acting as a viral reservoir and incubator, although four bee viruses often associated with CCD (Kashmir bee, Slow paralysis, Acute bee paralysis and Israeli acute paralysis virus) were not influenced by Varroa in Hawaii.

One bee virus, the Deformed Wing Virus (DWV), has been implicated in colony losses, for example over wintering colony losses (OCL), as it appears to become ubiquitous wherever Varroa occurs.

DWV is naturally transmitted between bees via feeding or during mating. However, the mites introduce DWV directly into the bee's blood while feeding so creating a new viral transmission route that bypasses many of the bees' natural defensive barriers.

DWV is a tiny virus similar in structure to polio or foot and mouth virus and has only 9 genes.

DWV infected bees may display the classic wing deformity, but the vast majority of infected bees do not show any morphological signs of infection.

The dominant strain found on Oahu and now Big Island is identical to that found in other areas of the world indicating that the situation on Hawaii is a mirror to what has happened right across the globe.

Based on comparisons between the 2009 and 2010 the changes in viral diversity associated with Varroa appear stable and persist even after the parasite levels are reduced via mite treatments.