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Thread: Nosema in bumble bees

  1. #11
    Administrator gavin's Avatar
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    Quote Originally Posted by greengumbo View Post
    Something odd right enough about this study. 30% is very low 'prevalence'. They did find replicating virus though. Hmmmm.
    GG (or anyone), how did they know the virus was replicating*? I saw the distinction in a supplementary table but didn't see their justification for discriminating the two.

    I hear that they captured bees (Apis and Bombus) at the same site using a net. How can they be sure that they are not cross-contaminating samples at the point of collection?

    I don't see why they used variables like number of sunshine hours to fine tune their model ....

    'including biologically relevant interactions while controlling for latitude, longitude and sunlight hours, and adding collection site and species identity as random factors. Our full model for DWV presence fitted the data significantly better than the null model without any of the test predictors and their interactions included (likelihood ratio test: X2519.03, d.f.55, P,0.002). '

    ... sounds like tinkering, no? And are we really to believe that fine-scale local variations in DWV/Varroa presence on honeybees influences levels of virus in bumble bees in the same local area? If so, how? Surely a mile or so down the road beekeeping practice will be different and DWV/Varroa levels different? And are Varroa supposed to do this apparently wholesale Apis-Bombus disease transfer?

    *PS
    What I mean is the distinction made in the paper between virus which is just present from virus which is replicating.
    Last edited by gavin; 26-02-2014 at 09:40 AM.

  2. #12
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    Hey gavin....no idea why they do the all the control variables. It seems like fiddling around the edges to me as the model must be influenced by a million other things before considering sunshine etc. I'm not convinced that bumbles and honeybees come into contact much anyway. I wonder if a "DWV-like" virus is simply circulating in bumble bee populations anyway ? Much like DWV in honeybees was at benign levels until Varroa came on the scene ?

    Anyway in the methods bit they say "we tested all of our DWV positive Bombus samples and a subset of DWV positive Apis samples for virus replication, a strong indicator for infection. DWV is a positive strand virus whose negative strand is only present in a host once the virus is actively replicating". So this is a bit technical BUT you do a reverse transcription using a specific DWV primer in your first strand synthesis. This then acts as the priming site for PCR and, importantly, would only show a product if you have detected negative strand virus...ie replicating virus. However you need to run a shed load of controls to be sure the original primer you used for tagging is not acting independently from the RT and giving you false positives. My bible....the BEEBOOK....has a chapter of virology in bees that talks about this.

  3. #13
    Administrator gavin's Avatar
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    Thanks GG. The issue of shed-loads of controls is the thing that worries me. They are making extraordinary claims (rapid, abundant, local intergenus viral transfer despite the lack of a convincing vector), and so the refereeing process should demand extraordinary levels of care. With the scant technical details available in a Nature paper you just can't judge the quality of the work. However word from some of those who have had a chance to debate this work prior to publication is that their results and conclusions were contentious, I hear.

    One possible explanation for their results is, for example, that they cross-contaminated samples both way (Apis to Bombus and maybe vice versa) during or after collection. As you say, it seems conceiveable that species of Bombus could harbour their own strains of DWV-like viruses, just as Apis mellifera did before Varroa came along and amplified one variant.

    Thanks for the comments on negative-strand virus copies indicating viral replication. If, say, Apis was actively replicating a certain virus and material (broken body hair for example) was transferred to other bees sampled in the same equipment is it conceiveable that the other bees would then have detectable replicating virus?

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