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Otto

Dangerous bee virus might be innocent bystander

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https://www.sciencedaily.com/releases/2019/01/190129195223.htm?utm_source=feedburner&utm_medium=email&utm_campaign=Feed%3A+sciencedaily%2Fplants_animals%2Fviruses+(Virology+News+--+ScienceDaily)

 

The scientific paper on which this article was based is available at:

https://royalsocietypublishing.org/doi/10.1098/rspb.2018.2452

Abstract

The arrival of the ectoparasitic mite Varroa destructor on the western honeybee Apis mellifera saw a change in the diversity and prevalence of honeybee RNA viruses. One virus in particular, deformed wing virus (DWV) has become closely associated with V. destructor, leading many to conclude that V. destructor has affected viral virulence by changing the mode of transmission. While DWV is normally transmitted via feeding and faeces, V. destructor transmits viruses by direct injection. This change could have resulted in higher viral prevalence causing increased damage to the bees. Here we test the effect of a change in the mode of transmission on the composition and levels of honeybee RNA viruses in the absence of V. destructor. We find a rapid increase in levels of two viruses, sacbrood virus (SBV) and black queen cell virus (BQCV) after direct injection of viral extracts into honeybee pupae. In pupae injected with high levels of DWV extracted from symptomatic adult bees, DWV levels rapidly decline in the presence of SBV and BQCV. Further, we observe high mortality in honeybee pupae when injected with SBV and BQCV, whereas injecting pupae with high levels of DWV results in near 100% survival. Our results suggest a different explanation for the observed association between V. destructor and DWV. Instead of V. destructor causing an increase in DWV virulence, we hypothesize that direct virus inoculation, such as that mediated by a vector, quickly eliminates the most virulent honeybee viruses resulting in an association with less virulent viruses such as DWV.

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I haven't had complete read of this paper yet but what they suggest (hypothesise) is that DWV is actually a far less virulent virus than some of the other viruses, which are apparently eliminated due to their virulence. Not sure I completely agree with this conclusion... One of the viruses they used to test this was sacbrood virus, which I think still seems to be prevalent at much the same rate as pre-varroa (judging by the odd encounter I have with what looks like sacbrood). 

I think the more likely scenario is that DWV is very efficiently vectored by varroa while these other viruses are not. 

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Its an interesting read - and I need to read it again.

One of the issues I have . . we frequently (bordering on always) find high levels of BQCV in bee samples. . .  its the DWV levels that vary. Perhaps it is a synergistic effect.

Also, the DWV samples they used were from New Zealand (Aussie paper). As they admit, they do not have varroa and thus are they testing the correct strains (ie they haven't been 'selected' by Australian varroa.

I agree with you @Otto - especially as varroa is indeed reported to replicate in varroa (as well as in the chalkbrood fungus)

 

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10 hours ago, JohnF said:

especially as varroa is indeed reported to replicate in varroa (as well as in the chalkbrood fungus)

@JohnF does that say what you meant?

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Sorry, meant ‘especially as *DWv” is indeed reported to replicate in varroa’

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