Deformed wing virus of honey bees is inactivated by cold plasma ionized hydrogen peroxide

Abstract

Deformed wing virus (DWV) is a widespread pathogen of Apis mellifera honey bees, and is considered a major causative factor for the collapse of infected honey bee colonies. DWV can be horizontally transmitted among bees through various oral routes, including via food sharing and by interactions of bees with viral-contaminated solid hive substrates. Cold plasma ionized hydrogen peroxide (iHP) is used extensively by the food production, processing and medical industries to clean surfaces of microbial contaminants. In this study, we investigated the use of iHP to inactivate DWV particles in situ on a solid substrate. iHP-treated DWV sources were ~10⁵-fold less infectious when injected into naïve honey bee pupae compared to DWV receiving no iHP treatment, matching injected controls containing no DWV. iHP treatment also greatly reduced the incidence of overt DWV infections (i.e., pupae having >10⁹ copies of DWV). The level of DWV inactivation achieved with iHP treatment was higher than other means of viral inactivation such as gamma irradiation, and iHP treatment is likely simpler and safer. Treatment of DWV contaminated hive substrates with iHP, even with honey bees present, may be an effective way to decrease the impacts of DWV infection on honey bees.

Keywords: Apis mellifera; DWV; IHP; Varroa destructor; infectivity.

Figure 1

Experimental design. Aliquots of PBS either with or without DWV were placed on a non-porous surface, allowed to dry, then either treated or untreated with ionized hydrogen peroxide (iHP). Aliquots were recovered from surfaces and then injected in naïve honey bee pupae. DWV infection progressed for three days prior to pupae being analyzed for their DWV content (i.e., number of genome equivalents).

Figure 2

(A) Boxplot shows development of virus infection (log₁₀ copy number of DWV) in honey bee pupae 3 days after injection with PBS (Control), 10⁵ and 10⁶ copies of DWV recovered from the surfaces and for the latter, either untreated (Not-iHP-treated) or treated with ionized hydrogen peroxide for 30 minutes (iHP-treated). Dots represent virus levels in individual pupae. Different ded letters above boxes indicate significantly different groups (p < 0.05, pairwise Wilcoxon test). (B) Percent of honey bee pupae having greater than 10⁹ GE of DWV.