Kashmir Bee Virus: Last, but Not Least Virulent

Thursday 2 September 2021

Our exploration of honey bee viruses continues this week with the topic of the Kashmir bee virus (KBV). Kashmir bee virus is being increasingly associated with colony collapse disorder in apiaries and, as such, is a serious and lethal virus.

First, we would like to share an interesting update from a newly published article* about deformed wing virus. Deformed wing virus is in part spread by Varroa mites, which act as a vector for virus transmission. DWV is also spread via shared floral sources, not only among honey bees, but between honey bee and bumblebee communities. This paper demonstrates, via mathematical modelling, that simultaneously controlling Varroa populations and increasing floral abundance can create a dilution effect and consequently reduce the spread of DWV between bee communities. 

Kashmir Bee Virus: Last, but Not Least Virulent

Kashmir bee virus is not a virus which can be easily detected through recognizable symptoms. In fact, the virus is often present in low concentrations in colonies which appear otherwise healthy. It is only after being triggered by a stressor that the virus begins to rapidly multiply and symptoms, including death, become abruptly apparent.  At this point, the virus can lead to entire colony collapse. A common stressor associated with the multiplication of Kashmir bee virus is high levels of Varroa destructor. Varroa mite infestations cause the virus to flare and have also been identified as a source of transmission between colonies, though more research needs to be done to fully explore this insight. Kashmir bee virus has also been found to transmit orally and has been detected in brood, food, honey, pollen, royal jelly, and faeces. A third source of transmission is vertically from a queen to her laid eggs. In laboratory settings, the Kashmir bee virus has demonstrated to be the most infectious of all honey bee viruses, reproducing quickly and able to reach lethal levels in three days. The virus has been detected in bees of all life stages. It is most threatening to adults, causing mortality within a few days. Larvae are more often asymptomatic but can also die from infection.

The Kashmir bee virus, first isolated from an Asian honey bee in the Kashmir region of India, is closely related to the acute bee paralysis virus. The virus has been found in apiaries across the globe but is most prevalent in the United States and Australia. Fortunately, the virus is not presently common in Canada. There are some actions that will help keep infestation rates in Canada low, including active control of Varroa mites, Nosema, and EFB in apiaries. This can prevent spread and mitigate stressors which might cause low concentrations of Kashmir bee virus to multiply and turn into a deadly situation.

Figure 1. Varroa mite on a honey bee. Kashmir bee virus can exist in otherwise healthy-looking bees. Varroa mites trigger the virus to reach lethal levels. (Photo credit: Alex Wild)

The Kashmir bee virus concludes our blog series on honey bee viruses. Identifying and managing these viruses is an essential part of beekeeping in order to maintain strong and healthy colonies year after year. One theme which has stood out throughout this overview has been the link between viruses and Varroa mites. Varroa mites often act as a vector of viruses, a contributing factor to the severity of the virus, or both. Controlling Varroa mites is an excellent first line of defense against harmful viral infections in honey bee colonies. 

*Burnham, P.A., S. Alger, B. Case, H. Boncristiani, L. Hébert-Dufresne, A. Brody.  2021. Flowers as dirty doorknobs: Deformed wing virus transmitted between Apis mellifera and Bombus impatiens through shared flowers, Journal of Applied Ecology., Available ONILNE. 

OMAFRA [Ontario Ministry of Agriculture, Food and Rural Affairs] 2021. Honey bee pests and pathogens in Ontario apiaries, 2015. Food Safety and Environmental Division, Animal Health and Welfare Branch. Available ONLINE.

Pernal, S. F. and Clay, H. (eds.) 2013. Honey bee diseases and pests, 3rd Edition. Canadian Association of Professional Apiculturists, Beaverlodge, AB, Canada 68 pp.

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. Available ONLINE.

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