Byrne Andrew W, Graham Jordon, Brown Craig, Donaghy Aoibheann, Guelbenzu-Gonzalo Maria, McNair Jim, Skuce Robin, Allen Adrian, McDowell Stanley
Agri-food and Biosciences Institute, Veterinary Science Division, Stormont, Belfast, Northern Ireland, BT43SD, UK.
School of Biological Sciences, Queen's University Belfast, Belfast, Northern Ireland, UK.
BMC Vet Res. 2017 Dec 29;13(1):400. doi: 10.1186/s12917-017-1321-z.
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.
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; 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).
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.
牛结核病（bTB）由牛分枝杆菌引起，在包括北爱尔兰在内的世界许多国家的畜牧业中仍然是一个重大问题，自1959年以来，北爱尔兰的检测和屠宰制度一直采用单剂量皮内比较颈结核菌素（SICCT）检测。我们使用两个模型套件，调查了在畜群疫情期间基于牛结核病可见病变（VL）存在情况的死后确诊差异。我们研究了动物层面的特征，同时控制畜群层面的因素和聚类情况。我们关注并发感染的潜在影响，因此评估了有肝吸虫感染证据（肝片吸虫；死后检查）、鸟分枝杆菌反应动物（牛分枝杆菌-鸟分枝杆菌（b-a）结核菌素反应阴性的动物）或牛病毒性腹泻病毒（BVDV；逆转录聚合酶链反应检测）的动物是否与牛结核病确诊有关。
数据集包括在14个月研究期间（2013 - 2015年）被移除的6242只动物。在披露SICCT检测中b-a反应大小更大的动物中，牛结核病-VL的存在显著增加（例如，b-a = 5 - 9毫米与b-a = 0毫米，调整后的优势比（aOR）：14.57；p < 0.001）。鸟分枝杆菌反应动物（b-a < 0）也比非反应动物（b-a = 0）更有可能出现VL（aOR：2.29；p = 0.023）。动物在其居住过的畜群数量增加（移动；对数畜群：aOR：2.27 - 2.42；p < 0.001）、如果其倒数第二次检测结果不确定（aOR：2.84 - 3.89；p < 0.001）以及检测间隔时间增加（对数时间；aOR：1.23；p = 0.003）时，出现病变的可能性更大。如果动物是奶牛品种（aOR：0.79；p = 0.015）或处于较高年龄组（例如，年龄四分位数2与4；aOR：0.65；p < 0.001），则出现VL的可能性较小。肝吸虫或BVDV变量在两个多变量模型中均未保留，因为它们与牛结核病-VL状态无显著关联（p > 0.1）。
我们的结果表明，肝吸虫或BVDV的共感染对这个高风险队列中VL的存在没有显著影响。鸟分枝杆菌结核菌素反应动物出现牛结核病病变的风险显著增加，这可能与副结核分枝杆菌亚种（MAP）的共感染影响SICCT检测性能有关，然而该领域需要进一步研究。移动、检测历史、品种和年龄是影响高风险动物确诊的重要因素。
