Deformed Wing Virus: A Persistent Pathogen of Honey Bees

Thursday 5 August 2021

Managing pests and disease is necessary in order to maintain healthy honey bee colonies.  This presents one of the biggest challenges to maintaining vigorous bee hives and successful over wintering.  Therefore, competent beekeepers are aware specifically of the damage caused by the varroa mite but may be less aware of viral diseases of honey bees.  Also there may be limited awareness of how these mites and viruses synergistically harm our bees.  Varroa mites are a means of spread, or a vector, for a range of viral diseases and over the next few weeks we will provide some information on a few.  We will start this series by looking at Deformed Wing Virus.

Deformed Wing Virus: A Persistent Pathogen of Honey Bees

There are more than 20 viruses which can infect honey bees but one of the most common and easily identifiable is the Deformed Wing Virus (DWV).  So, unlike other viruses which may be less visible, the symptoms of DWV are obvious to the observant beekeeper.  The body malformations resulting from DWV infection are shown in the figure.  This RNA virus, base on the nucleic acids which make up its genome, is ubiquitous.  One study, indicated that DWV was found in 100% of varroa mites in countries where testing was conducted (Tantillo et al, 2015).  The virus can be transmitted horizontally via the varroa mite.  The strong association between varroa infestation and deformed wing virus is such that the malformation of the wings was originally thought to be caused by the loss of hemolymph due to varroa infestation.  Later molecular diagnostic techniques disproved this theory but DVW and varroa still go hand-in-hand.

The DWV exists as two well known strains, the DWV-A and DWV-B, as well as a recently discovered third or C strain.  As with all viral strains, evolutionary pressure causes changes in the dominant strain.  It is thought that DWV-B is currently dominant with DWV-C perhaps emerging.  This will of course be determined by the host, individual or colony, susceptibility to the different variants.

Figure 1. Honey bee with wing malformations due to Deformed Wind Virus.  Photo: Traynor, M.

The implications for foraging ability of DWV infected bees are obvious but there are perhaps more subtle damaging effects.  It is suggested that DWV alone cannot bring down a colony but will, if combined with varroa infestation, devastate a hive.  Viruses can exist as a covert-persistent infection or acute-overt infection.  The first type will reflect low levels of infection, show a slow replication rate and little or no outward symptoms.  The acute-overt infection manifests itself in obvious clinical symptoms and ill health of individual bees and the entire colony.  In the case of the DWV, the transition from covert-persistent to overt-acute may involve the varroa mite!

What is known is that Varroa destructor is a vector for the DWV.  The combination of an DWV infection and weakening effects of a high varroa load is thought to result in the devastation overt-acute infection.  So, although DVW can transmit vertically, for example from drones to queens or from queens to eggs, we know that varroa mites are a horizontal vector for DVW transmission.  It is also known that honey bees can maintain a covert -persistent DVW infection but a combined varroa mite infestation may act as a trigger leading to more damaging effects.

There is considerable research currently ongoing to better understand DVW.  For example, does the virus replicate in the mite is a question currently being explored.  What is obvious is that malformed wings of the honey bees will result in these newly emerged workers quickly dying and contributing nothing to the overall colony.  There also may be other effects on the bees which are as yet unknown.  We can be assured that there is a strong association between DVW and varroa mites and that this is a significant disease of the honey bee which can be managed through control of varroa mite populations.


Tantillo,G., M. Bottaro, A. Di Pinto, V. Martella, P. Di Pinto, V. Terio (2015) Virus infections of honeybees Apis Mellifera, Italian journal of food safety., 4.

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