Beginning in 1986 an epidemic of bovine spongiform encephalopathy (BSE) was identified in numerous European countries, most notably in the UK. Although it has not been definitively determined, this epidemic apparently arose via feeding ruminant-derived protein contaminated with the scrapie agent to cattle in the United Kingdom. It is suspected that rendering plant procedural changes in the 1970s resulted in the failure to inactivate the scrapie agent. Transmission by contaminated feed appears to have been the only mechanism by which cattle became infected. No evidence of horizontal spread from animal to animal has been documented in the BSE outbreak (96).
The BSE epidemic in the United Kingdom peaked in 1992 with over 3,500 new cases per month in cattle. Beginning in 1988, the United Kingdom instituted a number of control measures beginning with a ban prohibiting the feeding of ruminant-derived protein to ruminants. In 1990 this ban was extended to prohibit the feeding of specified bovine offal (brain, spinal cord, thymus, tonsil, spleen) to other ruminants, and in 1996 the mammalian meat and bone meal prohibition was instituted. The restrictions have worked to the extent that through the first half of 2004 only 233 cases have been reported to the Dept. of Environment, Food and Rural Affairs, the UK equivalent to the USDA. In calendar year 2003, 457 cases were reported (95-98).
In the United States, the feeding of rendered cattle products to other cattle has been prohibited since 1997, and the importation of cattle and cattle products from countries with BSE or considered to be at high risk for BSE has been prohibited since 1989. These measures have minimized the potential exposure of animals and humans to the BSE agent. Nonetheless, on December 23, 2003, the USDA made a preliminary diagnosis of BSE in a single nonambulatory dairy cow in Washington State. The BSE international reference laboratory in Weybridge, England, subsequently confirmed this diagnosis. This was the first time BSE has been identified in the United States (98,99).
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