Pathogen detection in early phases of experimental bovine tuberculosis

Authors: Palmer, Mitchell; Kanipe, Carly; HWANG, SOYOUN - Animal And Plant Health Inspection Service (APHIS); Thacker, Tyler; LEHMAN, KIMBERLY - Animal And Plant Health Inspection Service (APHIS); LEDESMA, NICHOLAS - Animal And Plant Health Inspection Service (APHIS); GUSTAFSON, KRISTOPHOR - Animal And Plant Health Inspection Service (APHIS); Boggiatto, Paola

Submitted to: Veterinary Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2024
Publication Date: 8/7/2024
Citation: Palmer, M.V., Kanipe, C.R., Hwang, S., Thacker, T.C., Lehman, K.A., Ledesma, N.A., Gustafson, K., Boggiatto, P.M. 2024. Pathogen detection in early phases of experimental bovine tuberculosis. Veterinary Sciences. 11(8). Article 11080357. https://doi.org/10.3390/vetsci11080357.
DOI: https://doi.org/10.3390/vetsci11080357

Interpretive Summary: Over 100 years ago, in 1917, USDA initiated a bovine tuberculosis (bTB) eradication program that is still in place today. Although significant progress has been made, eradication has proved elusive. One major obstacle to eradication is the lack of rapid and accurate diagnostic tests to detect animals infected with Mycobacterium bovis (M. bovis; the cause of tuberculosis in animals); specifically, tests to detect infection early in disease before cow-to-cow spread occurs. Most diagnostic assays measure an animal's response to infection. Instead, we examined various bodily fluids (blood, saliva, nasal secretions, and feces) for the presence of the causative organism, M. bovis during the first 8 weeks after infection. Using highly sensitive molecular methods we detected M. bovis in a low number of saliva and nasal secretion samples, but never in blood or feces. We were never able to isolate and culture M. bovis from these samples. If the future of bovine tuberculosis diagnosis is early pathogen detection, further work is needed to determine alternative samples for collection and/or detection assays.

Technical Abstract: Bovine tuberculosis is caused by Mycobacterium bovis, a serious zoonotic pathogen. Diagnosis of bovine tuberculosis has relied on examination 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. tuberculosis complex 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. tuberculosis complex DNA was not found in blood samples collected weekly and examined by real-time PCR. Interferon gamma release assays and tuberculin skin testing 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.