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Evaluation of a Fecal Shedding Test To Detect Badger Social Groups Infected with Mycobacterium bovis.

ABSTRACT: 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 feces. The Animal and Plant Health Agency (APHA) of the United Kingdom organized a comparative trial to determine the performance of tests in detecting M. bovis in badger feces for the Department for Environment, Food, and Rural Affairs (DEFRA). Here, we assessed 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% confidence interval [CI], 94.5 to 99%; n = 244) and a specificity of 99% (95% CI, 97.8 to 100%; n = 292). Fast96-qPCR requires further optimization. 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 second positive result. Fast24-qPCR with repeat testing had a sensitivity of 87.3% (95% CI, 83.1 to 91.5%; n = 244), and a specificity of 100% (95% CI, 100 to 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.

SUBMITTER: Murphy ARJ

PROVIDER: S-EPMC7771468 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Tuberculosis (TB) vaccination could be used as a key part of integrated strategies for the disease's control if an effective and safe vaccine under field conditions is obtained. Recent studies in Spain have evaluated the protective efficacy of two oral vaccines against experimental challenge with live intra-bronchial Mycobacterium bovis in captive badgers: the live-attenuated M. bovis BCG vaccine (Danish strain) and a heat-inactivated M. bovis (HIMB) vaccine. With the objective of increasing the knowledge of the cellular development progress of infection and generating further tools to discriminate between mild and severe TB lesions between and within animals, the immunopathology of tuberculous lesions was studied to characterize the local immune response (cell type profile) within lung granulomas from control (non-vaccinated), BCG vaccinated and HIMB-vaccinated experimentally infected badgers with M. bovis. Four immunohistochemical protocols, for the specific detection of macrophages, T lymphocytes, B lymphocytes and plasma cells within TB granulomas in formalin fixed sections of the right middle lung lobe (lobe targeted for the M. bovis delivery), were performed. Immunolabelled sections were scanned and five randomly selected areas were analyzed with digital image analysis software. The results were expressed as the proportion of the positively immunolabelled area within the total area of the selected site. Data was analyzed using the statistical analysis software (SAS). In the three treatment groups, macrophages were the most abundant inflammatory cells within the granulomas, followed by B lymphocytes and plasma cells. T lymphocyes were absent in those granulomas. This would suggest a predominance of a non-specific innate response mediated by phagocytic cells over an adaptative humoral immune response. The proportion of macrophages and plasma cells was higher in BCG and HIMB-vaccinated badgers, respectively, suggesting the establishment of an adaptative humoral response in HIMB-vaccinated badgers. The lower bacterial load at the lung level, as well as the volume of lesions in lungs using magnetic resonance imaging in badgers with the HIMB vaccine in relation with local immune response presented, must be highlighted, since it would be an advantage in favor of its use under field conditions in terms of reducing TB transmission and environmental contamination.

Project description:Bovine tuberculosis is a chronic inflammatory disease that causes granuloma formation. Characterization of granulomatous lesions of Mycobacterium bovis (M. bovis) experimentally infected cattle has helped to better understand the pathogenesis of this disease. However, few studies have described granulomas found in M. bovis naturally infected cattle. The aim of this work was to examine granulomas from Holstein-Friesian cattle naturally infected with M. bovis from a dairy basin located in the central region of Mexico. Tissue samples from thirty-two cattle with lesions suggestive of tuberculosis were collected post-mortem. Fifteen of the 32 sampled animals (46.8%) were 4 months of age or younger (calves), whereas the rest (53.2%, 17/32) were over one year old (adults). Macroscopic lesions suggestive of tuberculosis were found in the mediastinal lymph node chain of all animals (32/32). From the 1,143 granulomatous lesions that were microscopically analyzed, 34.6% (396/1143) were collected from adult animals and subsequently classified according to the nomenclature suggested by Wangoo et al., 2005. Surprisingly, lesions from calf tissues showed an atypical pattern which could not be fitted into the established developmental stages of this classification. Granulomatous lesions found in calves covered most of the affected organ, histologically showed large necrotic areas with central calcification, absence of a connective tissue capsule, and few giant cells. Also, there was a higher percentage of lesions with acid-fast bacilli (AFB) when compared to studied granulomas in adults. Growth of Mycobacterium spp was detected in 11 bacteriological tissue cultures. Genotypic identification of M. bovis was performed by DNA extraction from bacterial isolates, formalin-fixed and paraffin-embedded (FFPE) tissues and samples without bacterial isolation. M. bovis was detected by PCR in 84.3% (27/32) of the studied cases; whereas other AFB were observed in tissues of the remaining sampled animals (5/32). Our results describe atypical granuloma formation in calves 4 months of age or younger, naturally infected with M. bovis. These findings contribute to better understanding the physiopathology of M. bovis infection in cattle.

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Evaluation of a Fecal Shedding Test To Detect Badger Social Groups Infected with Mycobacterium bovis.

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