Bovine tuberculosis visible lesions in cattle culled during herd breakdowns: the effects of individual characteristics, trade movement and co-infection

Abstract

BackgroundBovine 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.ResultsThe 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; log-herds: 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).ConclusionsOur 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.Electronic supplementary materialThe online version of this article (10.1186/s12917-017-1321-z) contains supplementary material, which is available to authorized users.

Liver fluke (Fasciola hepatica) co‐infection with bovine tuberculosis (bTB) in cattle: A retrospective animal‐level assessment of bTB risk in dairy and beef cattle

“…Other research using a smaller dataset suggested that liver fluke status did not have an impact bTB lesion presence (Byrne et al. ) but was associated with smaller lesions (Byrne, Graham, Brown, et al. ).…”

“…This abattoir handles the majority of animals (~99%; Byrne et al. ) that were skin test (SICTT) test positive, and therefore the animals processed represent a wide geographic sample across NI (see Milne et al. for distributions).…”

“…A dataset was constructed of all animals which died over the period 2011-2013, and were processed in one abattoir. This abattoir handles the majority of animals (~99%; Byrne et al 2017) that were skin test (SICTT) test positive, and therefore the animals processed represent a wide geographic sample across NI (see Milne et al 2018 for distributions). All data were retrieved from the Animal and Public Health Information System (APHIS) of Northern Ireland (Houston 2001).…”

“…Spoligotyping was used to confirm the presence of M. bovis. Reaction size raw data were made available on a subset of animals within the dataset (primarily reactor (standard and severe) animals and negative in contacts; Byrne et al 2017;Byrne, Graham, Brown, et al 2018), which was reported in millimetres as recorded by callipers in the field.…”

Exploring the Risk Posed by Animals with an Inconclusive Reaction to the Bovine Tuberculosis Skin Test in England and Wales

“…In Ireland, IRs that were negative at re-test were followed over a four-year period, and 9.3% of these animals were subsequently diagnosed with TB compared to 2.6% of control animals [13]. In Northern Ireland, in a high-risk cohort, animals with an inconclusive penultimate skin test result had an elevated adjusted odds ratio (OR) of 2.84-3.89 (p < 0.001) relative to non-reactors for the presence of bTB lesions at slaughter [14]. In England and Wales, IR-only herds were 2.7 times more likely to have a subsequent incident compared with negative-testing herds, although this difference reduced over time [15].…”