Geographical clustering of cases of bovine spongiform encephalopathy (BSE) born in Switzerland after the feed ban.

Over one-third of the cases of BSE in Switzerland have been born after the feed ban of December 1, 1990. Evidence for the geographical clustering of these cases emerged in two distinct regions. All the 354 BSE cases recorded until June 30, 2000 (set A), and the 376 cases recorded up to May 14, 2001 (set B), were georeferenced to the centres of the communities in which the herds of origin were located, and control populations were georeferenced to the centres of the communities in which these herds were located at the time of the census. The latitudes and longitudes of these centres were used in the statistical analysis of the spatial clustering. The Cuzick-Edwards test and the spatial scan statistics were applied to assess the significance of the clusters, while controlling for the spatial distribution of the underlying cattle population. There was global clustering of the cases born after the ban, and distinct and significant (P<0.05) spatial clusters were repeatedly identified in the two case datasets, and in several control populations (all cases born before the feed ban on a random sample of control farms) in terms of cattle density by region or cow density by region. Differential reporting was excluded as the underlying reason for the observed clusters.

[A method to identify BSE suspects in emergency slaughtered cattle during ante mortem examination]. / Eine Methode zur Erkennung von BSE-Verdachtsfällen in der Gruppe der krankgeschlachteten Rinder während der ante mortem Untersuchung.

A method is presented by which a maximal number of BSE-infected cattle that had escaped the filter of clinical examination are identified during ante mortem examination. This approach might prove to be an efficient and cost-effective method for veterinary and non-veterinary meat inspectors to remove infected animals prior to slaughter. In a case-control study, the clinical signs of 224 randomly selected sick slaughtered animals were compared with the clinical signs of 26 sick slaughtered animals in which BSE infection was diagnosed using a rapid test post mortem. In addition, the clinical signs of the sick slaughtered BSE-positive animals were compared with the clinical signs of a group of BSE suspects identified during the same time period and in which BSE infection could be confirmed. As a result of this study a mathematical model was developed to identify BSE suspects. This model contains a total of 7 variables (clinical signs) that proved to be of importance. These signs were aggressive behaviour, grinding of teeth, protruding eyeballs, reduced rumination, inability to stand, overexcitability, and difficulty in standing up. The presented model has a sensitivity of 61.5% (16 out of 26 BSE-positive animals slaughtered while sick were identified) and a specificity of 99.6% when compared to a rapid test conducted post mortem.