In vivo and in vitro infection dynamics of honey bee viruses

Abstract

The honey bee (Apis mellifera) is commonly infected by multiple viruses. We developed an experimental system for the study of such mixed viral infections in newly emerged honey bees and in the cell line AmE-711, derived from honey bee embryos. When inoculating a mixture of iflavirids [sacbrood bee virus (SBV), deformed wing virus (DWV)] and dicistrovirids [Israeli acute paralysis virus (IAPV), black queen cell virus (BQCV)] in both live bee and cell culture assays, IAPV replicated to higher levels than other viruses despite the fact that SBV was the major component of the inoculum mixture. When a different virus mix composed mainly of the dicistrovirid Kashmir bee virus (KBV) was tested in cell culture, the outcome was a rapid increase in KBV but not IAPV. We also sequenced the complete genome of an isolate of DWV that covertly infects the AmE-711 cell line, and found that this virus does not prevent IAPV and KBV from accumulating to high levels and causing cytopathic effects. These results indicate that different mechanisms of virus-host interaction affect virus dynamics, including complex virus-virus interactions, superinfections, specific virus saturation limits in cells and virus specialization for different cell types.

Honey Bee Viruses in Wild Bees: Viral Prevalence, Loads, and Experimental Inoculation

“…The viral inoculum used here was produced by the methods of Carrillo-Tripp et al [33]. Note that the percent makeup described here is slightly different than in Carrillo-Tripp et al; variations occur in aliquots of the virus mixture due to storage time and aliquot.…”

“…This inoculum consists of a mix of viral species naturally occurring in honey bee colonies in the field. It is highly lethal to honey bees and, while SBV is the main component, results in significant elevation in IAPV titer after just 48 hours, showing that, when honey bees are fed this inoculum, IAPV replicates very quickly (within 48 hours), and is thus the likely the main virus causing high observed mortality [33]. …”

“…Each bee received a cotton wick soaked in 0.5 mL of 1:1000 dilution of viral inoculum in 30% sucrose solution or 0.5 mL of heat inactivated viral inoculum in 30% sucrose solution. Heat-inactivated virus was produced by heating aliquots of viral stocks to 95°C for 30 minutes, providing a negative control [33]. While not measured quantitatively, bees were regularly observed feeding on the sugar solution in the cotton wicks.…”

“…In the case of very large bees (e.g., bumble bees), the whole body was homogenized, then a subset of the tissue was used for extraction. Genome copy number of five viruses commonly detected in other studies and in our routine screenings of the Iowa State University research apiary was determined by absolute quantification approach by extrapolation to a standard curve of in vitro synthesized viral RNA, as described in Carrillo-Tripp et al [33]. These five viruses were black queen cell virus (BQCV), Israeli acute paralysis virus (IAPV), deformed wing virus (DWV), sacbrood virus (SBV), and Lake Sinai virus (LSV).…”

“…To determine the potential source of these viruses, we also explored whether honey bee presence at our collection sites was related to detection and titer of viruses in wild bees. To evaluate the effects of honey bee virus occurrence on non-honey bee, non-Apidae species, we examined mortality and virus level changes in two solitary bee species ( Colletes inaequalis and Megachile rotundata ) after treatment with viral inoculum known to cause substantial mortality in honey bees [33]. Together, these data provide critically needed information about honey bee virus incidence, load, and mortality induction in wild bees.…”