Deformed Wing Virus

Deformed Wing Virus (DWV) is an RNA virus, one of 18 known viruses affecting the honey bee, Apis mellifera. The virus was first isolated from a sample of symptomatic honeybees from Japan in the early 1980s and is currently distributed worldwide.

Symptoms
Deformed wing virus (DWV) is suspected of causing the wing and abdominal deformities often found on adult honeybees in colonies infested with Varroa mites. These symptoms include damaged appendages, particularly stubby, useless wings, shortened, rounded abdomens, miscoloring and paralysis. Symptomatic bees have severely reduced life-span (less than 48 hours usually) and are typically expelled from the hive. The symptoms are strongly correlated with elevated DWV titres, with reduced titres and prevalence in asymptomatic bees from the same colonies. In the absence of mites the virus is thought to persist in the bee populations as a covert infection, transmitted orally between adults and to the brood, and vertically through the queen ovaries and through drone sperm.

Transmission by Varroa destructor
The severe symptoms of DWV infections appear to be associated with Varroa destructor infestation of the bee hive and studies have shown that Varroa destructor harbors greater levels of the virus than are found even in severely infected bees. Thus V. destructor may not only be a concentrating vector of the virus but may also act as a replicating incubator, magnifying and increasing its affects on the bees and on the hive. The combination of mites and DWV causes immunosuppression in the bees and increased susceptibility to other opportunistic pathogens and has been considered a significant factor in honey bee colony collapse disorder.

The virus may also be transmitted from queen to egg and in regurgitated food sources, but in the absence of V. destructor this does not typically result in large numbers of deformed bees.

Kakugo virus and aggressive behavior
Another virus, the Kakugo virus, has an RNA sequence that is 98% similar to DWV. It is found only in the mushroom bodies of aggressive, guard honeybees. Bees that are significantly affected by DWV also have measurable titers of the virus in their heads while bees that are symptomless only produce titers in their abdomens or thoraxes. Some researchers have detected increased aggressiveness immediately before colony collapse, and suspect that the virus may play a role. Other researchers have dismissed this relationship.