Monitoring of Paenibacillus larvae in Lower Austria through DNA-Based Detection without De-Sporulation: 2018 to 2022

SIMPLE SUMMARY: American foulbrood is a deadly disease specific for honey bees. The infectious agent, Paenibacillus larvae, is a spore-forming bacterium. Symptoms of the disease are often seen at a very late stage. Early detection, before the disease has done any harm, is useful in controlling the burden of the disease. This is accomplished in monitoring and surveillance programs often organized by local authorities. Detection of this bacterium is time-consuming as it involves a de-sporulation process. Here, we describe a five-year voluntary monitoring program in a western district of Lower Austria based on traditional pathogen detection and direct DNA-based detection without the need for de-sporulation. ABSTRACT: American foulbrood is caused by the spore-forming Paenibacillus larvae. Although the disease effects honey bee larvae, it threatens the entire colony. Clinical signs of the disease are seen at a very late stage of the disease and bee colonies are often beyond saving. Therefore, through active monitoring based on screening, an infection can be detected early and bee colonies can be protected with hygiene measures. As a result, the pressure to spread in an area remains low. The cultural and molecular biological detection of P. larvae is usually preceded by spore germination before detection. In this study, we compared the results of two methods, the culture detection and RT-PCR detection of DNA directly isolated from spores. Samples of honey and cells with honey surrounding the brood were used in a five-year voluntary monitoring program in a western part of Lower Austria. DNA-extraction from spores to speed up detection involved one chemical and two enzymatic steps before mechanical bashing-beat separation and additional lysis. The results are comparable to culture-based methods, but with a large time advantage. Within the voluntary monitoring program, the proportion of bee colonies without the detection of P. larvae was high (2018: 91.9%, 2019: 72.09%, 2020: 74.6%, 2021: 81.35%, 2022: 84.5%), and in most P. larvae-positive bee colonies, only a very low spore content was detected. Nevertheless, two bee colonies in one apiary with clinical signs of disease had to be eradicated.