Superinfection Exclusion in Honey Bees explains long-term survival of Varroa infested colonies. Deformed wing virus strain:Type A/ Type B

Over the past 50 years, countless of millions of managed and feral honey bee (Apis mellifera) colonies have died as the ecto-parasitic mite Varroa destructor has spread into the West1,2. The mite has introduced a new viral transmission route that has dramatically altered the viral landscape2. This has resulted in a massive loss of diversity in Deformed Wing Virus (DWV)3, the pathogen now linked with the collapse of honey bee colonies2,4,5. However, prior to Varroa spread, DWV stably co-existed with honey bees2 albeit at viral loads many orders of magnitude lower than is now observed2,6. In the West, very few and often isolated A. mellifera populations infested with Varroa survive without direct human intervention. Here we discovered a phenomenon known as Superinfection exclusion (SIE)7,8 that could explains why one such isolated UK A. mellifera population has survived for nearly two decades, despite high Varroa and DWV loads. Mass sequencing of these hives has identified a non-lethal variant of DWV (type B), which has become established in both A. mellifera and Varroa populations that show no evidence of the lethal ‘type A’ DWV variant. This appears to be achieved by recombining out the lethal variant; a host-pathogen relationship which, notwithstanding major differences in the immune systems of bees and humans, bears a striking resemblance to Edward Jenner’s 18th century discovery that pre-exposure to the relatively innocuous cowpox virus went on to protect milkmaids against the deadly smallpox virus. Building on this original vaccination example, this novel bee virus-interaction would seem to hold great promise for the development of an effective prophylactic treatment for use in the battle against this highly destructive virus.