Honey bee health decline represents a problem of global importance for the remarkable impact of these
pollinators on the environment and human economy. The reduced bee survival is the result of a multifactorial
syndrome triggered by several stress factors that synergistically interact. A common element to all collapsing
colonies is the high loads of parasites and associated pathogens, such as Deformed Wing Virus (DVW). DWV
is an endemic immunosuppressive virus that generates asymptomatic covert infections, kept in check by the
bees’ immune system when not exposed to stress agents which weaken antiviral barriers. Here we focused
on the effects of DWV infection on the modulation of honey bee gut microbiota, which plays a key-role in gut
physiology and immunity. We compared the microbiota composition of field-collected bees with low and
high DWV levels, pointing out the occurrence of a gut dysbiosis in highly infected bees, characterized by a
reduced level of Lactobacillusspecies and an increased level of Rhizobiaceae (Proteobacteria). The same kind
of dysbiosis is observed in adult bees injected with viral lysate under lab conditions, suggesting that this
community shift is likely the result of an active DWV infection during microbiota colonization and
establishment in the gut. The comprehension of DWV effect on microbiota will deepen our knowledge about
immunosuppressive strategies used by viruses for host exploitation and will allow us to define blends of
probiotic microorganisms which may help to rescue the decay of honey bee immune competence
