Bovine tuberculosis visible lesions in cattle culled during herd breakdowns: the effects of individual characteristics, trade movement and co-infection
Date
2017-12
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Publisher
Springer
Abstract
Background: Bovine tuberculosis (bTB), caused by Mycobacterium bovis, remains a significant problem for livestock
industries in many countries worldwide including Northern Ireland, where a test and slaughter regime has utilised
the Single Intradermal Comparative Cervical Tuberculin (SICCT) test since 1959.
We investigated the variation in post-mortem confirmation based on bTB visible lesion (VL) presence during herd
breakdowns using two model suites. We investigated animal-level characteristics, while controlling for herd-level
factors and clustering. We were interested in potential impacts of concurrent infection, and therefore we assessed
whether animals with evidence of liver fluke infection (Fasciola hepatica; post-mortem inspection), M. avium reactors
(animals with negative M. bovis-avium (b-a) tuberculin reactions) or Bovine Viral Diarrhoea Virus (BVDV; RT-PCR tested)
were associated with bTB confirmation.
Results: The dataset included 6242 animals removed during the 14 month study period (2013–2015). bTB-VL presence
was significantly increased in animals with greater b-a reaction size at the disclosing SICCT test (e.g. b-a = 5-
9 mm vs. b-a = 0 mm, adjusted Odds ratio (aOR): 14.57; p < 0.001). M. avium reactor animals (b-a < 0) were
also significantly more likely to disclose VL than non-reactor animals (b-a = 0; aOR: 2.29; p = 0.023). Animals had a
greater probability of exhibiting lesions with the increasing number of herds it had resided within (movement; logherds: aOR: 2.27–2.42; p < 0.001), if it had an inconclusive penultimate test result (aOR: 2.84–3.89; p < 0.001), and with
increasing time between tests (log-time; aOR: 1.23; p = 0.003). Animals were less likely to have VL if they were a dairy
breed (aOR: 0.79; p = 0.015) or in an older age-class (e.g. age-quartile 2 vs. 4; aOR: 0.65; p < 0.001). Liver fluke
or BVDV variables were not retained in either multivariable model as they were non-significantly associated
with bTB-VL status (p > 0.1).
Conclusions: Our results suggest that neither co-infection of liver fluke nor BVDV had a significant effect on
the presence of VLs in this high-risk cohort. M. avium tuberculin reactors had a significantly increased risk of
disclosing with a bTB lesion, which could be related to the impact of co-infection with M. avium subsp. paratuberculosis
(MAP) affecting the performance of the SICCT however further research in this area is required. Movements, test history,
breed and age were important factors influencing confirmation in high-risk animals.
Description
Publication history: Accepted - 14 December 2017; Published online - 29 December 2017.
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Article
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Keywords
Bovine TB, Mycobacterium bovis, BVDV, Liver fluke, Paratuberculosis, Co-infection, Johne's disease, MAP, Fascioliasis, Gamma interferon, Skin tests, Cattle
Citation
Byrne, A. W., Graham, J., Brown, C., Donaghy, A., Guelbenzu-Gonzalo, M., McNair, J., Skuce, R., Allen, A. and McDowell, S. (2017) ‘Bovine tuberculosis visible lesions in cattle culled during herd breakdowns: the effects of individual characteristics, trade movement and co-infection’, BMC Veterinary Research, 13(1). doi: 10.1186/s12917-017-1321-z.