ANSES-Lyon, 31 avenue Tony Garnier, Lyon cedex 7, 69364, France.
BMC Vet Res. 2012 May 30;8:74. doi: 10.1186/1746-6148-8-74.
Cattle with L-type (L-BSE) and H-type (H-BSE) atypical Bovine Spongiform encephalopathy (BSE) were identified in 2003 in Italy and France respectively before being identified in other countries worldwide. As of December 2011, around 60 atypical BSE cases have currently been reported in 13 countries, with over one third in France. While the epidemiology of classical BSE (C-BSE) has been widely described, atypical BSEs are still poorly documented, but appear to differ from C-BSE. We analysed the epidemiological characteristics of the 12 cases of L-BSE and 11 cases of H-BSE detected in France from January 2001 to late 2009 and looked for individual risk factors. As L-BSE cases did not appear to be homogeneously distributed throughout the country, two complementary methods were used: spatial analysis and regression modelling. L-BSE and H-BSE were studied separately as both the biochemical properties of their pathological prion protein and their features differ in animal models.
The median age at detection for L-BSE and H-BSE cases was 12.4 (range 8.4-18.7) and 12.5 (8.3-18.2) years respectively, with no significant difference between the two distributions. However, this median age differed significantly from that of classical BSE (7.0 (range 3.5-15.4) years). A significant geographical cluster was detected for L-BSE. Among animals over eight years of age, we showed that the risk of being detected as a L-BSE case increased with age at death. This was not the case for H-BSE.
To the best of our knowledge this is the first study to describe the epidemiology of the two types of atypical BSE. The geographical cluster detected for L-BSE could be partly due to the age structure of the background-tested bovine population. Our regression analyses, which adjusted for the effect of age and birth cohort showed an age effect for L-BSE and the descriptive analysis showed a particular age structure in the area where the cluster was detected. No birth cohort effect was evident. The relatively small number of cases of atypical BSE and the few individual data available for the tested population limited our analysis to the investigation of age and cohort effect only. We conclude that it is essential to maintain BSE surveillance to further elucidate our findings.
L 型（L-BSE）和 H 型（H-BSE）非典型牛海绵状脑病（BSE）分别于 2003 年在意大利和法国被发现，随后在世界其他国家也有发现。截至 2011 年 12 月，13 个国家目前共报告约 60 例非典型 BSE 病例，其中三分之一以上发生在法国。虽然经典 BSE（C-BSE）的流行病学已得到广泛描述，但非典型 BSE 的记录仍不完善，但似乎与 C-BSE 不同。我们分析了 2001 年 1 月至 2009 年末在法国发现的 12 例 L-BSE 和 11 例 H-BSE 的流行病学特征，并寻找个体危险因素。由于 L-BSE 病例在全国的分布似乎不均匀，因此使用了两种补充方法：空间分析和回归建模。由于其病理性朊病毒的生化特性和在动物模型中的特征不同，因此分别研究了 L-BSE 和 H-BSE。
L-BSE 和 H-BSE 病例的检测中位年龄分别为 12.4 岁（范围 8.4-18.7 岁）和 12.5 岁（范围 8.3-18.2 岁），两者分布无显著差异。然而，该中位年龄与经典 BSE（7.0 岁（范围 3.5-15.4 岁））有显著差异。L-BSE 检测到明显的地理聚集。在 8 岁以上的动物中，我们发现 L-BSE 病例的发病风险随着死亡年龄的增加而增加。H-BSE 则不然。
据我们所知，这是首次描述两种类型非典型 BSE 的流行病学特征。检测到的 L-BSE 地理聚集可能部分归因于背景测试牛群的年龄结构。我们的回归分析调整了年龄和出生队列的影响，结果显示 L-BSE 存在年龄效应，描述性分析显示在检测到聚集的区域存在特定的年龄结构。没有出生队列效应的证据。非典型 BSE 的病例数相对较少，且可供检测人群使用的个体数据有限，这限制了我们的分析仅限于调查年龄和队列效应。我们的结论是，必须维持 BSE 监测，以进一步阐明我们的发现。
