Infection timelines and co-infection effects of Israeli acute paralysis virus and deformed wing virus in the honey bee (Apis mellifera)

Abstract

Honey bees are often exposed to and infected by multiple viruses, including deformed wing virus (DWV) and Israeli acute paralysis virus (IAPV). These pathogens are major contributors to colony failure, threatening the supply of pollination services in agriculture. However, understanding and modeling the infection and transmission dynamics of these viruses is hampered by gaps in knowledge about their infection timelines, specifically how virus load changes post-exposure. Moreover, while honey bees frequently experience co-occurring infections from multiple viruses, little is known about how co-infection affects virus-induced mortality and replication dynamics. We hypothesized that, while both DWV and IAPV are known to be highly infectious and can cause honey bee mortality, each presents a distinct infection timeline and peak infection intensity time window. In addition, we hypothesized that co-infection would result in increased mortality compared to individual virus infections due to increased pathogen-induced stress. To test these hypotheses, we exposed day-old honey bee workers to DWV, IAPV, or a combination of DWV and IAPV via carefully controlled experimental injections and tracked mortality and virus levels over time. After exposure, bees were maintained in the laboratory for 10 days and sampled daily for virus quantification. We observed a similar response pattern to both honey bee viruses in the first 24 h post-infection, where virus levels rapidly increased following inoculation. While DWV infection had persistently high virus levels and a delayed mortality response after peak DWV load was achieved, IAPV infection was rapidly followed by either mortality or a decline in virus load as bees recovered from infection. Co-infected bees showed some variation in mortality, although there were no significant differences in virus load between DWV or IAPV within co-infected bees compared to bees infected with the individual viruses. These results help answer fundamental questions related to the pathology of DWV and IAPV within honey bees that help clarify how these pathogens interact and persist within honey bee colonies.

Keywords: Deformed wing virus; Honey bee; Infection timeline; Israeli acute paralysis virus; Virus co-infection.