Open access paper with a fascinating conclusion -- please read the full paper.  The authors find evidence of low impact DWV strains resident in colonies with a history of survival, and propose a mechanism of "superinfection exclusion" -- functionally a vaccine to DWV that allows continued health in the face of normally lethal Varroa loading. 

Superinfection exclusion and the long-term survival of honey bees in Varroa-infested colonies

Gideon J Mordecai , Laura E Brettell , Stephen J Martin , David Dixon , Ian M Jones  and Declan C Schroeder 

http://www.nature.com/ismej/journal/vaop/ncurrent/full/ismej2015186a.html
http://dx.doi.org/10.1038/ismej.2015.186

Abstract

Over the past 50 years, many millions of European honey bee (Apis mellifera) colonies have died as the ectoparasitic mite, Varroa destructor, has spread around the world. Subsequent studies have indicated that the mite’s association with a group of RNA viral pathogens (Deformed Wing Virus, DWV) correlates with colony death. Here, we propose a phenomenon known as superinfection exclusion that provides an explanation of how certain A. mellifera populations have survived, despite Varroa infestation and high DWV loads. Next-generation sequencing has shown that a non-lethal DWV variant ‘type B’ has become established in these colonies and that the lethal ‘type A’ DWV variant fails to persist in the bee population. We propose that this novel stable host-pathogen relationship prevents the accumulation of lethal variants, suggesting that this interaction could be exploited for the development of an effective treatment that minimises colony losses in the future.

             ***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software.  For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html