Deformed wing virus in bee bread: infectivity and thermal inactivation

Abstract

Bee-collected pollen is stored in the colony and mixed with bee saliva and microorganisms, resulting in pollen’s fermentation and acidification. Pathogens infecting the colony, including the deformed wing virus (DWV), may be transferred into the bee bread (BB). In this study, we used an in vivo infection assay to determine whether DWV remains infective in BB. We also used Lactobacillus kunkeei to ferment UV-treated fresh pollen. This fermented pollen in vitro (FPV) was used as a virus-free reference for the initial viral loads in BB and to evaluate the effect of controlled bacterial fermentation on the infectivity of DWV. Finally, we investigated the thermal inactivation of DWV in BB and FPV. To accomplish these goals, we added DWV inoculum to BB and FPV and heated them at 70 °C or 60 °C for 1 h. Suspensions of the virus recovered from the treated pollen samples were injected into pupae to evaluate the degree of viral viability and the efficacy of thermal inactivation. We found that the virus recovered from non-thermally treated BB and FPV samples remained highly infectious in the pupal injection assay. Overall, BB and FPV treated at 60 °C had an average reduction of 98.69% of viable DWV copies, while treatments at 70 °C inactivated DWV almost entirely (99.99%). This study demonstrates that DWV remains infective in BB and that thermal inactivation is an effective strategy for significantly reducing levels of viable DWV in contaminated pollen.