This paper describes the results of analyses of the epidemiological features of the 164 cases of bovine spongiform encephalopathy (BSE) in Great Britain that were born after the introduction of the reinforced legislation introduced on August 1, 1996 (BARB cases) and that were detected before December 31, 2008. This additional control measure prohibited the use of mammalian meat and bone meal (MMBM) in feed for farm animals to prevent further exposure of cattle to the BSE agent. There was a pronounced reduction in the risk of infection, by three orders of magnitude, for cattle born after July 31, 1996 compared with that for cattle born earlier, and a statistically significant exponential reduction in the estimated prevalence between successive annual birth cohorts after this date. There was no evidence that a significant number of these cases occurred as a result of a maternally associated risk factor, infection from environmental contamination (other than from feedstuffs) or as a result of a genetically based aetiology. The epidemiological features were consistent with an exogenous feedborne source as a result of a reliance on imported feedstuffs in Great Britain and the later introduction of a ban on the use of MMBM in other EU member states on January 1, 2001.
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