Bee mortality: a new deformed wing virus mutant

Antivirus is not just limited to humans. Bees have their types, too, with their own set of variables. This is the case of the deformed wing virus (DWV for deformed wing virus) of which a new variant has just been described. And this new pathogen is not only more aggressive than its predecessor, but it spreads at a high speed. This could explain the increase in deaths observed during the winter of 2021-2022.

As you can imagine, a bee with deformed wings will find it difficult to fly, and as shown in the corresponding photo, the wings are deformed to the point where only the trunks remain.

According to one finding, recently published in the “International Journal of Parasitology: Parasitology and Wildlife,” the mutated pathogen is spreading rapidly throughout the world. “The new DWV-B mutation is more lethal and probably transmitted more easily than the original pathogens,” says Robert Paxton, a zoologist at Martin Luther University in Halle-Wittenberg, Germany. Infected animals usually die after 10 to 14 days.

How the virus kills bees is not entirely clear. Deformed wings typical of the disease only appear in infected animals already in the pupal stage and then hatch with defective wings due to infection. But even adult bees, whose outward appearance does not contradict anything, can become infected with pathogens and die from them. “Sick animals move around a lot less and can’t do their jobs in the cell either,” Paxton says. Most infected colonies die in the winter. The virus takes two to three years to destroy the entire colony.

“Most infected colonies die back in the winter,” Paxton says. There is still no medicine against the same virus that is transmitted by Varroa mites. The honeybee parasite, which is about one millimeter long and one and a half millimeters wide, sucks blood, or more precisely hemolymph, from the bees and thus transmits the deformed wing virus. “It’s kind of like mosquitoes and malaria pathogens,” Paxton says.

According to the study authors, there are indications that the new DWV-B mutant, unlike the original virus, is not only transmitted by the Varroa mite, but also reproduces within the parasite. In their study, the scientists hypothesize that “this could represent an additional mechanism that would increase the incidence of DWV-B compared to DWV-A.” Type B wing deformation virus was first discovered in 2001 in the Netherlands.

Sixteen percent of its genome has been modified compared to variant A. These modifications seem to give the virus huge advantages. This is the only way to show that the aggressive DWV-B variant spreads very quickly and replaces the original virus. To determine the prevalence of the new variant, Paxton and his team analyzed genetic data and publications on DWV viruses present in honeybees around the world between 2008 and 2021. In addition, the researchers themselves collected samples from Germany, Great Britain and Italy.

Here’s what they found: “The new variant of the virus is now present on all continents except Australia” where Varroa has also been absent. In the 2000s, DWV-B spread mainly in Europe and Africa. Since 2010, it has also spread to North and South America, and since 2015, it has been detectable in Asia. “In Germany, there is only variant B now,” Paxton says. According to him, it has completely replaced variant A.

Wild bees are also worried. Some species, such as ground bees, are known to be infected with deformed wing virus. Fortunately for wild bees, transmission of the virus to them by Varroa mites is fortunately rare, even unlikely, because these parasites primarily attack honey bees.

Source: Tina Baier, Tages-Anzeiger Online, 06.06.2022

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