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Simple Summary: Bovine tuberculosis is caused by Mycobacterium bovis, which causes tuberculosis in humans and animals. Diagnosis of bovine tuberculosis has relied on examination of immune responses to M. bovis; however, using these methods, disease detection during the earliest phases of infection has been difficult, allowing a window for cattle-to-cattle transmission to occur within a herd. Alternative means of diagnosis could include methods to detect M. bovis or M. bovis DNA in bodily fluids such as nasal secretions, saliva, or blood rather than the animal's response to infection. DNA-from M. bovis was detected in nasal swabs and saliva from a small number of experimentally infected calves during the first 8 weeks after experimental infection. Although DNA from M. bovis could be detected, no culturable M. bovis was recovered from nasal swabs or saliva. Moreover, M. bovis DNA was not found in blood samples collected weekly. Successful infection of all calves was demonstrated using an interferon gamma release assay. Identification of infected animals through the detection of M. bovis will require the use of alternative samples or alternative assays. Bovine tuberculosis is caused by Mycobacterium bovis, a member of the M. tuberculosis complex of mycobacterial species that cause tuberculosis in humans and animals. Diagnosis of bovine tuberculosis has relied on examinations of cell-mediated immune responses to M. bovis proteins using tuberculin skin testing and/or interferon gamma release assays. Even when using these methods, disease detection during the earliest phases of infection has been difficult, allowing a window for cattle-to-cattle transmission to occur within a herd. Alternative means of diagnosis could include methods to detect M. bovis or M. bovis DNA in bodily fluids such as nasal secretions, saliva, or blood. During the first 8 weeks after experimental aerosol infection of 18 calves, M. bovis DNA was detected in nasal swabs from a small number of calves 5, 6, and 8 weeks after infection and in samples of saliva at 1, 7, and 8 weeks after infection. However, at no time could culturable M. bovis be recovered from nasal swabs or saliva. M. bovis DNA was not found in blood samples collected weekly and examined by real-time PCR. Interferon gamma release assays demonstrated successful infection of all calves, while examination of humoral responses using a commercial ELISA identified a low number of infected animals at weeks 4–8 after infection. Examination of disease severity through gross lesion scoring did not correlate with shedding in nasal secretions or saliva, and calves with positive antibody ELISA results did not have more severe disease than other calves. [ABSTRACT FROM AUTHOR] |
