A Comparison of Different Matrices for the Laboratory Diagnosis of the Epizootic American Foulbrood of Honey Bees

SIMPLE SUMMARY: American Foulbrood is a bacterial disease of honey bee larvae caused by the spore-forming bacterium Paenibacillus larvae. It is a notifiable epizootic in most countries because it is highly contagious and lethal to affected colonies. For clinically diseased colonies, authorities often consider burning the only sustainable control measure, while infected but not yet diseased bee colonies can be cured by beekeeping measures. It is therefore of the utmost importance to identify such colonies. For the detection of P. larvae spores in infected colonies prior to the onset of clinical symptoms, different hive matrices can be used: brood comb honey, adult bees, seasonal hive debris, and winter hive debris. We evaluated the suitability of these matrices as sample materials for early P. larvae spore detection and demonstrate considerable differences in the growth of concomitant bacteria interfering with P. larvae detection and in the sensitivity and limit of detection of P. larvae spores. We conclude that brood comb honey and adult bees are equally well-suited as sample materials for the early detection of P. larvae spores, while hive debris samples should only be used when it is not possible to collect honey or adult bee samples from brood combs. ABSTRACT: American Foulbrood (AFB) of honey bees caused by the spore-forming bacterium Paenibacillus larvae is a notifiable epizootic in most countries. Authorities often consider a rigorous eradication policy the only sustainable control measure. However, early diagnosis of infected but not yet diseased colonies opens up the possibility of ridding these colonies of P. larvae spores by the shook swarm method, thus preventing colony destruction by AFB or official control orders. Therefore, surveillance of bee colonies for P. larvae infection followed by appropriate sanitary measures is a very important intervention to control AFB. For the detection of P. larvae spores in infected colonies, samples of brood comb honey, adult bees, or hive debris are commonly used. We here present our results from a comparative study on the suitability of these matrices in reliably and correctly detecting P. larvae spores contained in these matrices. Based on the sensitivity and limit of detection of P. larvae spores in samples from hive debris, adult bees, and brood comb honey, we conclude that the latter two are equally well-suited for AFB surveillance programs. Hive debris samples should only be used when it is not possible to collect honey or adult bee samples from brood combs.