Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Grønnegårdsvej 8, DK-1870 Frederiksberg C, Denmark.
Prev Vet Med. 2012 Dec 1;107(3-4):160-9. doi: 10.1016/j.prevetmed.2012.06.002. Epub 2012 Jun 29.
A national surveillance programme for Salmonella Dublin, based on regular bulk-tank milk antibody screening and movements of cattle, was initiated in Denmark in 2002. From 2002 to end of 2009 the prevalence of test-positive dairy herds was reduced from 26% to 10%. However, new infections and spread of S. Dublin between herds continued to occur. The objective of this study was to investigate factors affecting incidence risk of S. Dublin infection in Danish dairy herds between 2003 and 2009. Herds were considered at risk when they had been test-negative for at least four consecutive year-quarters (YQs), either at the start of the study period or after recovery from infection. Survival analysis was performed on a dataset including 6931 dairy herds with 118,969 YQs at risk, in which 1523 failures (new infection events) occurred. Predictors obtained from register data were tested in a multivariable, proportional hazard model allowing for recurrence within herds. During October to December the hazard of failures was higher (hazard ratio HR=3.4, P=0.0005) than the rest of the year. Accounting for the delay in bulk-tank milk antibody responses to S. Dublin infection, this indicates that introduction of bacteria was most frequent between July and October. Purchase from test-positive cattle herds within the previous 6 months was associated with higher hazard of failures (HR=2.5, P<0.0001) compared to no purchase and purchase from test-negative herds. Increasing local prevalence, herd size and bulk-tank milk somatic cell counts were also associated with increasing hazard of failures. The effect of prior infection was time-dependent; the hazard of failures was reduced following a logarithmic decline with increasing time at risk. The hazard was markedly higher in herds with prior infections the first year after becoming at risk again, and then approached the hazard in herds without known prior infections 2-3 years after becoming test-negative. This showed that herds with prior infections need to maintain a high level of biosecurity for at least 3 years after becoming test-negative for S. Dublin to prevent recurrence. Furthermore, general recommendations for dairy herds wishing to protect their herds against S. Dublin include avoidance of purchase from and contact to test-positive herds. Large herds, herds with test-positive neighbours and herds with high somatic cell counts need to obtain and maintain a high level of biosecurity.
丹麦于 2002 年启动了一项基于定期大容量牛奶抗体筛查和牛群流动的都柏林沙门氏菌国家监测计划。2002 年至 2009 年底，检测呈阳性的奶牛场的流行率从 26%降至 10%。然而，新的感染和都柏林沙门氏菌在牛群之间的传播仍在继续。本研究的目的是调查 2003 年至 2009 年期间影响丹麦奶牛场都柏林沙门氏菌感染发病率的因素。当牛群在研究开始时或从感染中恢复后至少连续四个季度（Q）检测为阴性时，这些牛群被视为处于风险之中。在包括 6931 个奶牛场和 118969 个有风险的 Q 的数据集上进行了生存分析，其中发生了 1523 例失败（新感染事件）。从登记数据中获得的预测因素在多变量、比例风险模型中进行了测试，允许在牛群中再次发生。10 月至 12 月，失败的风险较高（风险比 HR=3.4，P=0.0005），而一年中的其他时间则较低。考虑到大容量牛奶抗体对都柏林沙门氏菌感染的反应延迟，这表明细菌的引入最频繁发生在 7 月至 10 月之间。与无购买和从检测阴性牛群购买相比，在过去 6 个月内从检测阳性牛群购买与更高的失败风险相关（HR=2.5，P<0.0001）。当地流行率、牛群规模和大容量牛奶体细胞计数的增加也与失败风险的增加有关。先前感染的影响与时间有关；随着风险时间的增加，失败的风险呈对数下降。在再次处于风险中的第一年，有先前感染的牛群的失败风险明显更高，然后在 2-3 年后接近无先前感染的牛群的失败风险。这表明，有先前感染的牛群需要在成为都柏林沙门氏菌检测阴性后至少 3 年保持高水平的生物安全，以防止再次发生。此外，希望保护其牛群免受都柏林沙门氏菌感染的奶牛场的一般建议包括避免从检测阳性的牛群购买和接触。大型牛群、有检测阳性邻居的牛群和体细胞计数高的牛群需要获得并保持高水平的生物安全。
