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Kashmir Bee Virus (KBV) was diagnosed in the Fraser Valley in the spring of 2004, in a commercial operation whose honeybee colonies had declined and subsequently died. It has also been recently found in colonies that appear healthy.
The virus had previously been diagnosed in British Columbia in the early 1980s, in honeybee stock originally imported from Australia and New Zealand. At that time, well before the Varroa mite arrived, no symptoms had been observed and therefore, KBV was not a concern.
In the late 1980s, researchers in Europe and the US reported that KBV was a highly contagious and virulent pathogen in the presence of Varroa mites. Over the years, little information became available about KBV and its distribution and impact, since colony losses were mostly attributed to mite parasitism or other causes without proof. KBV and other viral honeybee agents may not have received much attention because disease symptoms were generally not as definitive as others, while laboratory analysis required expertise and resources.
The precise distribution of KBV in North America is not known. KBV was detected in 1995 in a small US survey of seven states. All states were positive: California, Florida, Maine, Minnesota, New York, Texas, and Washington. It has been suggested that the virus is endemically present throughout most of North America’s honeybee population.
The Kashmir Bee Virus is a natural disease of the eastern honeybee Apis cerana. After the introduction of the western honeybee Apis mellifera into the distribution range of A. cerana in southern Asia, the virus made a “species-jump” and began to parasitize its new host.
KBV of honeybees is a RNA-virus in the newly established family Dicistroviridae. RNA viruses are very small (in comparison to DNA-viruses) and associated with the mitochondria of host cells.
KBV’s virulence is made possible because of its association with the Varroa mite. Mites carry the viruses externally and internally. By piercing the honeybee’s cuticle, they transfer viral particles into the host’s tissue. The bee’s pupal stage appears most susceptible to infection. In the confined space of the capped pupal cell, viruses are not only transferred from mite to bee, but also from mite to mite. After several mite generations in the honeybee colony, the majority of mites will be KBV carriers. As more bees become infected, the transfer of food, grooming and other physical contact between bees facilitates the further spread of the virus.
It is not known whether the honey bee tracheal mite (Acarapis woodi) and Nosema (Nosema apis) are viral vectors as well. Since these pathogens cause tissue damage in the tracheal tubes and epithelial cell wall of the midgut of adult bees respectively, they may play a role in the introduction of viral agents into the host’s body cavity.
At this time, the causes that trigger virulence are unclear. Throughout the 1980s, the presence of KBV in BC colonies was an academic curiosity, as the virus remained non-virulent or in a latent state. Even after the introduction of Varroa in British Columbia in 1990, there were no reports of viral infestations. In recent years, occasional incidents of colony losses that could not be attributed to common honeybee diseases may have involved KBV.
Some studies have shown that high mite levels result in high virulence. This correlation can be readily accepted as large numbers of KBV-carrying mites contribute to the rapid spread of the virus throughout the bee population, while stress caused by mite parasitism increases the honeybee’s susceptibility to viral infection. However, surveys carried out by BC Ministry of Agriculture indicate that KBV virulence also occurs when Varroa infestation levels are low or non-detectable.
There is no prescribed set of symptoms confirming KBV in the field. Definitive diagnosis is carried out in the laboratory through Polymerase Chain Reaction (PCR) analysis. However, beekeepers may observe various symptoms that may point to viral infection. These include:
For definitive identification, whole adult bees must be analyzed in the laboratory. Adult bees are highly perishable and need to be preserved as best as possible after collection. The following collection method is recommended:
There is no product available for KBV control. Most viral infections become evident when bees have been stressed due to other diseases, weather conditions or management practices. Some bee stocks have shown higher susceptibility to viral infection than others; this can be remedied by replacing the queen with a queen from another source.
To minimize the impact of KBV and other viral infections:
For more information, contact the Apiculture office in Abbotsford
at 604-556-3129 / 604-556-3152.