Review of the monitoring and control of BSE in Europe

Marcus G. Doherr

Bovine spongiform encephalopathy (BSE), the transmissible spongiform encephalopathy (TSE) in cattle, was first described in 1987 in the United Kingdom. Evidence that cattle BSE and the human new variant of Creutzfeldt-Jakob disease (vCJD) could be caused by the same agent, and the potential that BSE has spread into the small ruminant population resulted in increased research and surveillance activities.

By December 31, 2001, domestic BSE cases had been detected in all but two EU member states as well as in Switzerland, the Czech Republic, the Ukraine, Slovenia, Slovakia and in Japan, and additional countries followed. Clinical signs of both BSE and SR-TSE can vary widely; a neurological examination of sick cattle, sheep and goats can only lead to a suspicion of a TSE. Histopathology and immunohistochemistry (IHC) are the gold standard confirmatory tests for ruminant TSE. Recently developed and validated rapid screening assays are now used for broad scale screening of cattle, sheep and goats that leave the population through four “exit routes”: routine slaughter (after “negative” ante mortem inspection), emergency slaughter (too sick for routine slaughter), fallen stock (found dead or culled), and BSE/scrapie suspects (with suspicious neurological signs).

Reporting of clinical suspects alone is insufficient to assess the disease situation in a given country or region. Within the EU Member States (excluding UK), of all BSE cases detected in between January 1, 2001 and December, 31, 2001, only 32% (range 0-60%) were confirmed clinical (suspect) cases. With more than three years of intensive BSE surveillance data available for Switzerland one can start to assess trends over time. In a combined evaluation of emergency-slaughtered cattle and fallen stock the prevalence clearly declined. The difficulty in analysing the routine-slaughter category is the very low prevalence. One approach to visualize trends is to calculate moving averages, another is to pool data over consecutive time intervals. Both approaches for Switzerland again showed decreasing BSE prevalence estimates over time. In the EU Member States, a total of 7.65 Million healthy-slaughtered cattle, 0.7 Million emergency-slaughtered cattle and fallen stock, 2423 clinical BSE suspects and 56056 cattle from effected farms (in the framework of BSE eradication) were examined in the year 2001 alone, and 969 BSE cases were detected. By mid of 2003, more than 23 Million cattle from the EU Member States (excluding UK) had been tested for the presence of PrPSc and almost 2400 BSE cases were detected within this mandatory surveillance program. Almost 90% of these tests were performed on healthy-slaughtered cattle, however, over 50% of all BSE cases were detected within the risk animal category, thereby highlighting the importance of that target population in BSE surveillance. The annual prevalence of BSE test-positive cattle in the three target populations ranged from 5- 11 per 100 examined cattle among the clinical suspects, 3-5 per 10000 among the tested risk animals, and 3-4 per 100000 among the healthy-slaughtered cattle. When analysing the BSE prevalence data within the risk animal and routine-slaughter population by month (pooled over countries) one can see a clear downwards trend among the risk animals.

An ongoing careful evaluation of the functionality and results of the implemented BSE surveillance systems is required in order to correctly assess the epidemiological situation. It seems possible to eradicate feed-born BSE once the feed transmission cycle is completely broken. This, however, takes as long as the implementation time for the measures, and the incubation time of the disease in cattle.

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Review of the monitoring and control of BSE in Europe

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Risk management strategies: monitoring and surveillance

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Review of the monitoring and control of BSE in Europe

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Risk management strategies: monitoring and surveillance

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