Bovine Spongiform Encephalopathy or âMad Cow Diseaseâ and New Variant Creutzfeldt-Jakob Disease
The issue of whether there is a direct link between the exposure to diseased animals and the acquisition of CJD has been the subject of much scientific study and debate. In the United Kingdom, scientists have ascertained a likely connection between bovine spongiform encephalopathy ("BSE") and CJD. BSE or "mad cow disease" was initially discovered in the United Kingdom in 1986 and thought to have resulted from the use of cattle feed containing contaminated meat and bone meal made from scrapie-infected sheep and/or TSE-infected cattle. The original outbreak was then probably magnified by subsequently feeding meat and bone meal from BSE-infected cows to young calves. The incidence of BSE in the United Kingdom reached its peak of over 36,000 confirmed cases in one year in 1992, and has been steadily declining. There have been over 180,000 BSE cases worldwide, with the overwhelming majority, over 95%, occurring in the United Kingdom. The other countries in which BSE has been found include: Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Ireland, Israel, Italy, Japan, Luxembourg, Liechtenstein, the Netherlands, Poland, Portugal, Slovakia, Slovenia, Spain, and Switzerland. The number of BSE cases in countries outside of the United Kingdom is increasing. BSE has not been detected in the United States.
On March 20, 1996, the United Kingdomâs Spongiform Encephalopathy Advisory Commmitte (âSEACâ) indicated that there was a possible link between BSE and a new variant of CJD (âvCJDâ). The SEAC identified 10 patients, whose illness surfaced in 1994 and 1995, with a form of CJD which differed significantly from classical sporadic CJD in several respects. These ten patients were all under the age of 42, with an average age of 28, as opposed to the typical age of 63 for classical CJD. The average course of the duration of vCJD was 13 months, in contrast to the average 4 to 6 month duration for classical CJD. The electroencephalographic (âEEGâ) electrical activity in the brain for vCJD was different from classical CJD. While the brain pathology of the vCJD cases was identifiable as CJD, the pattern differed from classical CJD with the presence of large aggregates of prion protein plaques. Despite the absence of direct scientific evidence linking BSE and vCJD, the SEAC decided that the most likely explanation for the unusual outbreak was the consumption of beef from diseased cattle before 1989, when regulations were adopted for the disposal at slaughter of potentially infectious cattle offal, including brains, spinal cords and intestines, and for the cessation of feeding protein derived from ruminants (i.e. cows, sheep, goats, deer and elk) to ruminants. Subsequent studies have strengthened the connection between BSE and vCJD.
There have been over 100 cases of vCJD, most of which have occurred in the United Kingdom, and the numbers are still rising. A few cases of vCJD have been found in France, Ireland, Italy, and Hong Kong. Because the incubation period between exposure to the TSE agent and the onset of symptoms may be as long as 40 years, it is uncertain whether these vCJD cases may signal the beginning of an epidemic or whether the incidence of vCJD will remain low. At the present time, no vCJD has been discovered in the United States.
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