Evaluation of a fecal shedding test to detect badger social groups infected with Mycobacterium bovis

Bovine Tuberculosis (bTB) is an economically important disease affecting the cattle industry in England and Wales. bTB, caused by Mycobacterium bovis, also causes disease in the Eurasian badger (Meles meles), a secondary maintenance host. Disease transmission between these two species is bidirectional. Infected badgers shed M. bovis in their faeces. The UK Animal and Plant Health Agency (APHA) organised a comparative trial to determine the performance of tests in detecting M. bovis in badger faeces for the Department for Environment, Food, and Rural Affairs (DEFRA). Here we present the performance of the existing Warwick Fast24-qPCR test, and its modified version based on a high-throughput DNA extraction method (Fast96-qPCR). We found Fast24-qPCR to have a sensitivity of 96.7% (95%CI 94.5-99%, n=244) and a specificity of 99% (95%CI 97.8-100%, n=292). Fast96-qPCR requires further optimisation. Determining the disease status of badger social groups requires multiple tests per group. Therefore to increase specificity further, we independently repeated the Fast24-qPCR test on positive samples, increasing stringency by requiring a 2nd positive result. Fast24-qPCR with repeat testing had a sensitivity of 87.3% (95%CI 83.1-91.5%, n=244), and a specificity of 100% (95%CI 100-100, n=201) on an individual sample level. At the social group level, this repeat testing gives Fast24-qPCR high herd specificity, while testing multiple samples per group provides high herd sensitivity. With Fast24-qPCR we provide a social group level test with sufficient specificity and sensitivity to monitor shedding in badgers via latrine sampling, delivering a potentially valuable tool to measure the impacts of bTB control measures