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Abstract
Three commercial honey bee operations in Saskatchewan, Canada, with outbreaks of American foulbrood (AFB) and recent or ongoing metaphylactic antibiotic use were intensively sampled to detect spores of Paenibacillus larvae during the summer of 2019. Here, we compared spore concentrations in different sample types within individual hives, assessed the surrogacy potential of honey collected from honey supers in place of brood chamber honey or adult bees within hives, and evaluated the ability of pooled, extracted honey to predict the degree of spore contamination identified through individual hive testing. Samples of honey and bees from hives within apiaries with a recent, confirmed case of AFB in a single hive (index apiaries) and apiaries without clinical evidence of AFB (unaffected apiaries), as well as pooled, apiary-level honey samples from end-of-season extraction, were collected and cultured to detect and enumerate spores. Only a few hives were heavily contaminated by spores in any given apiary. All operations were different from one another with regard to both the overall degree of spore contamination across apiaries and the distribution of spores between index apiaries and unaffected apiaries. Within operations, individual hive spore concentrations in unaffected apiaries were significantly different from index apiaries in the brood chamber (BC) honey, honey super (HS) honey, and BC bees of one of three operations. Across all operations, BC honey was best for discriminating index apiaries from unaffected apiaries (p = 0.001), followed by HS honey (p = 0.06), and BC bees (p = 0.398). HS honey positively correlated with both BC honey (rs = 0.76, p < 0.0001) and bees (rs = 0.50, p < 0.0001) and may be useful as a surrogate for either. Spore concentrations in pooled, extracted honey seem to have predictive potential for overall spore contamination within each operation and may have prognostic value in assessing the risk of future AFB outbreaks at the apiary (or operation) level.
Highlights
American foulbrood (AFB) is a destructive disease of honey bee larvae caused by the grampositive bacterium, Paenibacillus larvae [1]
We reported a description of these outbreaks in the context of relevant management practices as a means of continuing education for Canadian veterinarians, who have only recently become responsible for the Comparison of sample types for spores of Paenibacillus larvae in Saskatchewan honey bee operations prescription of antimicrobials for apiculture [37]
The objectives of this study were: i) to assess P. larvae spore concentrations from different sample types within individual hives across apiaries of beekeeping operations that had experienced recent outbreaks of AFB; ii) to assess whether honey collected from honey supers could be used as a surrogate for brood chamber honey or adult bees when assessing spore concentrations within a hive; and iii) to assess the ability of pooled honey samples collected during end-of-season extraction to predict the degree of spore contamination identified through individual hive sampling
Summary
American foulbrood (AFB) is a destructive disease of honey bee larvae caused by the grampositive bacterium, Paenibacillus larvae [1]. Prevention, eradication, and control of AFB are challenging due to the combination of spore resiliency and the dissemination of large numbers of spores throughout a hive by the normal caretaking actions of worker bees [10]. These same characteristics, have been useful in the development of diagnostic testing for the presence of spores in different hive- and colony-associated matrices [11]. These include bees, wax, pollen, bottom-board debris, and honey, all of which have been used as a diagnostic tool to determine the clinical status of a hive, or as a predictive tool to determine the risk of disease outbreak [1, 2, 6, 11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33]
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