A comprehensive analysis of the bovine spongiform encephalopathy (BSE) epidemic in cattle in Great Britain assesses past, present and future patterns in the incidence of infection and disease, and allows a critical appraisal of different culling policies for eradication of the disease.

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Disease surveillance programmes ought to be evaluated regularly to ensure they provide valuable information in an efficient manner. Evaluation of human and animal health surveillance programmes around the world is currently not standardized and therefore inconsistent. The aim of this systematic review was to review surveillance system attributes and the methods used for their assessment, together with the strengths and weaknesses of existing frameworks for evaluating surveillance in animal health, public health and allied disciplines. Information from 99 articles describing the evaluation of 101 surveillance systems was examined. A wide range of approaches for assessing 23 different system attributes was identified although most evaluations addressed only one or two attributes and comprehensive evaluations were uncommon. Surveillance objectives were often not stated in the articles reviewed and so the reasons for choosing certain attributes for assessment were not always apparent. This has the potential to introduce misleading results in surveillance evaluation. Due to the wide range of system attributes that may be assessed, methods should be explored which collapse these down into a small number of grouped characteristics by focusing on the relationships between attributes and their links to the objectives of the surveillance system and the evaluation. A generic and comprehensive evaluation framework could then be developed consisting of a limited number of common attributes together with several sets of secondary attributes which could be selected depending on the disease or range of diseases under surveillance and the purpose of the surveillance. Economic evaluation should be an integral part of the surveillance evaluation process. This would provide a significant benefit to decision-makers who often need to make choices based on limited or diminishing resources.

BackgroundRegular and relevant evaluations of surveillance systems are essential to improve their performance and cost-effectiveness. With this in mind several organizations have developed evaluation approaches to facilitate the design and implementation of these evaluations.MethodsIn order to identify and to compare the advantages and limitations of these approaches, we implemented a systematic review using the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses).ResultsAfter applying exclusion criteria and identifying other additional documents via citations, 15 documents were retained. These were analysed to assess the field (public or animal health) and the type of surveillance systems targeted; the development process; the objectives; the evaluation process and its outputs; and the attributes covered. Most of the approaches identified were general and provided broad recommendations for evaluation. Several common steps in the evaluation process were identified: (i) defining the surveillance system under evaluation, (ii) designing the evaluation process, (iii) implementing the evaluation, and (iv) drawing conclusions and recommendations.ConclusionsA lack of information regarding the identification and selection of methods and tools to assess the evaluation attributes was highlighted; as well as a lack of consideration of economic attributes and sociological aspects.

Animal health surveillance programmes may change in response to altering requirements or perceived weaknesses but are seldom subjected to any formal evaluation to ensure that they provide valuable information in an efficient manner. The literature on the evaluation of animal health surveillance systems is sparse, and those that are published may be unstructured and therefore incomplete. To address this gap, we have developed SERVAL, a SuRveillance EVALuation framework, which is novel and aims to be generic and therefore suitable for the evaluation of any animal health surveillance system. The inclusion of socio-economic criteria ensures that economic evaluation is an integral part of this framework. SERVAL was developed with input from a technical workshop of international experts followed by a consultation process involving providers and users of surveillance and evaluation data. It has been applied to a range of case studies encompassing different surveillance and evaluation objectives. Here, we describe the development, structure and application of the SERVAL framework. We discuss users' experiences in applying SERVAL to evaluate animal health surveillance systems in Great Britain.

In 1998, a questionnaire was sent to 11,554 British sheep farmers to determine how many believed that scrapie cases had occurred in their flock; 61.4 per cent of them responded anonymously. The results indicated that 14.9 per cent of farmers with more than 30 breeding ewes thought that they had ever experienced scrapie in their flock and 2.7 per cent thought that they had had cases in the past 12 months. A comparison of these results with the number of farmers reporting suspect scrapie cases to MAFF, in accordance with the statutory requirement, suggests that only 13 per cent of farmers who suspect that they may have cases of scrapie are currently reporting them. Scrapie occurred in all regions of the country but there was an apparent regional variation. Larger farms and those with purebred sheep appeared to be at greater risk of having cases. Other differences between affected and unaffected farms included lambing practices and sheep purchasing policy. On the majority of farms the first case occurred in a purchased animal. The survey also revealed a need for the provision of further information about scrapie to farmers.

Responses to an anonymous postal survey concerning scrapie are analysed. Risk factors associated with farms that have had scrapie are identi¢ed as size, geographical region, lambing practices and holding of certain breeds. Further analysis of farms that have scrapie only in bought-in animals reveals that such farms tend to breed a smaller proportion of their replacement animals than farms without scrapie. Farms that have had scrapie in home-bred animals have attributes associated with breeding many animals: large numbers of rams bought, few ewes bought, and many animals that are home-bred. The demography of British sheep farms as described by size, breeds, purchasing behaviour, age structure and proportion of animals that are home-bred is summarized. British farms with scrapie reveal certain special features: they have more sheep that are found dead, more elderly ewes and more cases of scab.