Real-time PCR as a decision aid in the control of European foulbrood

Abstract

The number of cases of European foulbrood (EFB) increased massively in Switzerland since 2000. According to Swiss legislation, the health status of all colonies within one kilometer from a case needs to be identified by a bee inspector. This results in a workload too high to be handled in due time in areas with a high prevalence and high colony density. Therefore, the primary goal of this study was testing the hypothesis that the number of visual inspections could be reduced if brood nest bees sampled by owners were tested by real-time PCR for the presence of Melissococcus plutonius, and results were assigned to one of the three categories “negative”, “positive,” or “strong positive” depending on the amount of bacterial DNA. Only apiaries with strong positive results were inspected visually. Furthermore, the development of the bacterial load over time was analyzed on an apiary level to determine whether this would allow predicting the outcome of an infection. For this purpose, bee samples of 88 apiaries were assayed by real-time PCR and visually inspected in parallel over several months. Comparison of the two methods revealed a sensitivity of the real-time PCR of 93.5% and a specificity of 58.6% relative to visual inspection. One month after first sampling the bacterial load was still on the same level in 54%, had increased in 17%, and decreased in 29% of 35 apiaries. Establishing predictions on the basis of real-time PCR results is therefore not possible. In conclusion, due to its poor specificity, preliminary real-time PCR would not allow reducing the number of visual inspections sufficiently to compensate the costs of additional laboratory diagnosis. However, real-time PCR may be a valuable tool for identifying infected colonies in the context of trade and migratory beekeeping.