Del Rio Vilas Victor Javier, Böhning Dankmar, Kuhnert Ronny
Veterinary Laboratories Agency, New Haw, Addlestone, Surrey, KT15 3NB, UK.
Vet Res. 2008 May-Jun;39(3):37. doi: 10.1051/vetres:2008014. Epub 2008 Feb 29.
The abattoir and the fallen stock surveys constitute the active surveillance component aimed at improving the detection of scrapie across the European Union. Previous studies have suggested the occurrence of significant differences in the operation of the surveys across the EU. In the present study we assessed the standardisation of the surveys throughout time across the EU and identified clusters of countries with similar underlying characteristics allowing comparisons between them. In the absence of sufficient covariate information to explain the observed variability across countries, we modelled the unobserved heterogeneity by means of non-parametric distributions on the risk ratios of the fallen stock over the abattoir survey. More specifically, we used the profile likelihood method on 2003, 2004 and 2005 active surveillance data for 18 European countries on classical scrapie, and on 2004 and 2005 data for atypical scrapie separately. We extended our analyses to include the limited covariate information available, more specifically, the proportion of the adult sheep population sampled by the fallen stock survey every year. Our results show that the between-country heterogeneity dropped in 2004 and 2005 relative to that of 2003 for classical scrapie. As a consequence, the number of clusters in the last two years was also reduced indicating the gradual standardisation of the surveillance efforts across the EU. The crude analyses of the atypical data grouped all the countries in one cluster and showed non-significant gain in the detection of this type of scrapie by any of the two sources. The proportion of the population sampled by the fallen stock appeared significantly associated with our risk ratio for both types of scrapie, although in opposite directions: negative for classical and positive for atypical. The initial justification for the fallen stock, targeting a high-risk population to increase the likelihood of case finding, appears compromised for both types of scrapie in some countries.
屠宰场和死亡牲畜调查构成了主动监测的组成部分，旨在提高整个欧盟对羊瘙痒病的检测。先前的研究表明，欧盟各国在这些调查的操作方面存在显著差异。在本研究中，我们评估了整个欧盟范围内这些调查随时间的标准化情况，并确定了具有相似潜在特征的国家集群，以便在它们之间进行比较。由于缺乏足够的协变量信息来解释各国之间观察到的变异性，我们通过对死亡牲畜与屠宰场调查风险比的非参数分布来模拟未观察到的异质性。更具体地说，我们对18个欧洲国家2003年、2004年和2005年关于经典型羊瘙痒病的主动监测数据，以及分别对2004年和2005年非典型性羊瘙痒病的数据使用了轮廓似然法。我们扩展了分析，纳入了可用的有限协变量信息，更具体地说，是每年死亡牲畜调查所抽样的成年绵羊群体比例。我们的结果表明，相对于2003年，2004年和2005年经典型羊瘙痒病的国家间异质性有所下降。因此，过去两年中的集群数量也减少了，这表明整个欧盟的监测工作正在逐步标准化。对非典型性数据的粗略分析将所有国家归为一个集群，并且显示两种监测来源中任何一种对这种类型羊瘙痒病的检测都没有显著增加。对于两种类型的羊瘙痒病，死亡牲畜调查所抽样的群体比例似乎都与我们的风险比显著相关，尽管方向相反：对于经典型为负相关，对于非典型性为正相关。在一些国家，死亡牲畜调查最初针对高风险群体以增加病例发现可能性的理由，对于两种类型的羊瘙痒病似乎都受到了影响。
