Reilly L A, Courtenay O
Ecology & Epidemiology Group, Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK.
Prev Vet Med. 2007 Jul 16;80(2-3):129-42. doi: 10.1016/j.prevetmed.2007.02.002. Epub 2007 Mar 8.
Bovine tuberculosis (bTB) is a persistent problem in cattle herds in Great Britain and Ireland. Farm management and cattle husbandry practices can influence the risk of transmission of bTB and hence the likelihood of bTB breakdown (>or=1 reactor to the tuberculin skin test). Biological differences are expected in the transmission dynamics, and hence risk factors for bTB breakdown, on farms where infection persists in the herd compared to farms where infection is more sporadic or short-lived. Comparative case-control studies were performed to test farm management practices as potential risk factors for transient (under breakdown restrictions for <or=6 months) and persistent (under breakdown restrictions for >6 months) bTB breakdown over 5 years (1995-1999) on 179 and 171 UK cattle farms, respectively. Farms were characterised for badger sett density and farm habitat composition by ground survey, farmers were questioned retrospectively on management practices, and cases and controls were identified from national tuberculin test records. Controlling for routine tuberculin testing interval, log-transformed herd size, regional location, badger sett density and farm habitat complexity, multivariable logistic regression identified increased odds of both transient and persistent breakdown on farms that bought-in cows (odds ratio (OR)>or=4.9; 95% confidence interval (CI)>or=1.1;22.8). In addition, the purchase of >50 head of cattle (OR=4.0, 95% CI=1.0;16.0) and the storage of manure for >or/=6 months (OR=4.4; 95% CI=1.3;15.4) were risk factors for transient breakdown, whereas the use of silage clamps (OR=9.1; 95% CI=2.0;40.8) increased the risk of persistent breakdown. Decreased odds of both transient and persistent breakdown were associated with higher stocking densities (>3cattle/ha) (OR<or=0.2; 95% CI<or=0.1;0.9), and running mixed herd enterprises compared to only beef or dairy (OR=0.1; 95% CI=0.0;0.7) was an additional protective factor against persistent breakdown. In these analyses, the covariates log herd size and tuberculin testing interval were significant predictors of both transient and persistent breakdown, whereas active badger sett density and regional location only affected the risk of persistent breakdown. The collective results suggest that the probability of transient breakdown is most strongly influenced by the purchase of cattle over other management variables and covariates, whereas the probability of persistent breakdown appears to be mostly affected by management factors relating to type of herd enterprise and silage storage in addition to the relative density of badgers. Implications for bTB management are discussed.
牛结核病（bTB）在英国和爱尔兰的牛群中一直是个问题。农场管理和养牛实践会影响牛结核病传播的风险，进而影响牛结核病疫情爆发（结核菌素皮肤试验反应动物≥1头）的可能性。预计在牛群感染持续存在的农场与感染较为零星或短暂的农场之间，传播动态以及牛结核病疫情爆发的风险因素存在生物学差异。开展了比较病例对照研究，以检验农场管理实践作为1995 - 1999年5年间英国179个和171个养牛场分别出现短暂（在疫情限制下≤6个月）和持续（在疫情限制下>6个月）牛结核病疫情爆发的潜在风险因素。通过地面调查确定獾穴密度和农场栖息地组成来描述农场特征，回顾性询问农民管理实践情况，并从国家结核菌素检测记录中获取病例和对照。在控制常规结核菌素检测间隔、对数转换后的牛群规模、区域位置、獾穴密度和农场栖息地复杂性后，多变量逻辑回归分析表明，购入奶牛的农场出现短暂和持续疫情爆发的几率均增加（优势比（OR）≥4.9；95%置信区间（CI）≥1.1；22.8）。此外，购入超过50头牛（OR = 4.0，95% CI = 1.0；16.0）以及粪便储存≥6个月（OR = 4.4；95% CI = 1.3；15.4）是短暂疫情爆发的风险因素，而使用青贮窖（OR = 9.1；95% CI = 2.0；40.8）会增加持续疫情爆发的风险。较高的饲养密度（>3头牛/公顷）与短暂和持续疫情爆发几率降低相关（OR≤0.2；95% CI≤0.1；0.9），与仅养殖肉牛或奶牛相比，经营混合牛群企业（OR = 0.1；95% CI = 0.0；0.7）是防止持续疫情爆发的另一个保护因素。在这些分析中，协变量对数牛群规模和结核菌素检测间隔是短暂和持续疫情爆发的显著预测因素，而活跃獾穴密度和区域位置仅影响持续疫情爆发的风险。总体结果表明，与其他管理变量和协变量相比，购入牛对短暂疫情爆发概率的影响最大，而持续疫情爆发概率似乎除了獾的相对密度外，还主要受与牛群企业类型和青贮储存相关的管理因素影响。文中讨论了对牛结核病管理的启示。
