OAHN Bee Project: Paenibacillus larvae spore testing in Ontario honey bee colonies (in progress)

Project Lead: Dr. Olaf Burke, Britteny Kyle

Collaborators: 

Project Proposal

American foulbrood (AFB) is the most devastating bacterial disease of honey bees.  It is caused by the gram-positive spore-forming bacterium Paenibacillus larvae (Genersch et al., 2006). Ontario beekeepers have historically relied upon metaphylactic antimicrobial administration for AFB management. Since 2018, however, the antimicrobials labelled for use in AFB control can only be obtained through veterinary prescription (Government of Canada, 2021). The requirement for veterinary involvement has created a potential barrier to antimicrobial access due to increased costs and difficultly finding veterinarians willing to take on beekeeper clients. Antimicrobials do not eliminate the infectious spore form and may, therefore, only suppress clinical expression of the disease. Colonies can be subclinically infected, with the risk of developing clinical AFB and the potential to spread the spores to other colonies within the local landscape via known horizontal transmission pathways such as beekeeper activity and robbing behaviour. Sudden discontinuation of antimicrobials may increase the risk of outbreaks within operations. With current management and surveillance practices the risk for clinical AFB outbreaks remains unknown to beekeepers.

While the prevalence of clinical AFB, as reported through the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) apiary inspection program, is known, it is important to determine the prevalence of subclinical infection. Additionally, it is important to learn about the distribution of background level of spores in apparently healthy colonies.  This knowledge informs about the risk of colonies becoming clinically infected, particularly where metaphylactic antimicrobials are discontinued.

Testing the level of spores in healthy colonies has the potential to be a useful long-term surveillance tool that would allow for a decrease in the reliance on medically-important antimicrobials. This would better align with antimicrobial stewardship in food-producing animals. To date, the majority of studies on spore loads have been carried out in countries that do not rely on metaphylactic antimicrobials and focussed on colonies with known increased risk of having spores due to recent cases of AFB within the operations under study (Zabrodski et al., 2022; Bassi et al., 2018; Bzdil, 2007; Gillard et al., 2008; Lindström & Fries, 2005).  It is important to evaluate the utility of spore testing within the context of Ontario apiculture.

Determination of spore counts from adult bees collected from the brood nest has been demonstrated to detect spores of P. larvae more often and with a higher sensitivity compared to other sources within the hive (Bassi et al., 2018; Gillard et al., 2008; Linström & Fries, 2005).  Other sampling sources, however, may be more efficient, more practical, less costly, and therefore more readily adopted by the beekeeping community.  Previous studies have shown that spores can be cultured and enumerated from various hive samples (Zabrodski et al., 2022; Bassi et al., 2018; Bzdil, 2007; Gillard et al., 2008; Lindström & Fries, 2005), however data has not been analysed to look at how well the results from the different samples taken from within the same colony agree.  If there is good agreement between samples that are more efficient for the beekeeper to collect, such as wax debris, or that are already being collected, such as bees from an alcohol wash, then these samples may be more suitable to incorporate into an AFB surveillance and management strategy.

During project planning, consultation was done with the Provincial Apiarist, Mr. Paul Kozak from OMAFRA, Drs. Durda Salvic and Hugh Cai from the Animal Health Laboratory (AHL), and Dr. Colette Mesher from the Ontario Beekeepers’ Association (OBA) Tech Transfer Program (TTP).  Discussions centred around sampling strategy, testing methodology, and ethical and legal considerations regarding positive results.