BOVINE SPONGIFORM ENCEPHALOPATHY

New Research shows that prions may not be the cause of BSE

Bovine spongiform encephalopathy, colloquially known as 'Mad Cow Disease' or by its acronym BSE, is a neurological disease of cattle which first appeared in the UK in the early 1980's following changes in the way in which winter feeds were prepared. The explanation accepted by the British government is that this disease is caused by prions, protein fragments which have been observed in scrapie-infected sheep. The use of abattoir offal, which may have included scrapie-infected sheep, in the production of winter feeds could have transmitted this disease to cattle.

However in early 1996, a paper appeared which suggested that scrapie could not be transmitted between SCID mice. This demonstrated that the disease was neither infectious nor contagious, but probably caused by the immune system of the animal itself. Researchers at King's College London have therefore proposed that BSE is an autoimmune disease caused by infection with microbes containing sequences which crossreact with the nervous tissues of sheep or cattle. This explanation has a similarity to the cases of ankylosing spondylitis and rheumatoid arthritis, both autoimmune diseases caused by Klebsiella and Proteus bacteria respectively.

It has been known since Pasteur first experimented in th 1880s, that the injection of brain tissues into allogeneic animals causes a neurological disease known as experimental allergic encephalomyelitis. EAE is characterized by tremors, paralysis of the hind quarters and eventual death: all features that are frequently observed in BSE.

Chronic EAE was demonstrated in 1969 to be characterized by the spongiform appearance of the brain, similar to the histological features observed in BSE or scrapie. Computer analysis of immunogenic sequences of bovine myelin were cross-referenced against bacterial protein databases and the microbe with the closest sequence to bovine myelin was found to be acinetobacter, a common saprophytic microbe, present in large quantities in soil, sewage and green offal. A sequence in the bacterium Escherichia coli (E. coli) was also identified which was similar to the prion protein. Accordingly, sera obtained from BSE cattle were tested for antibodies to acinetobacter and compared to healthy animals and it was found that BSE infected cattle contained elevated levels of acinetobacter antibodies.Raised levels of the antibody were also found in two cases of vCJD, and among patients with multiple sclerosis.

The conclusion reached by the researchers was that BSE is a neurological, autoimmune disease which occurs after cattle are exposed to acinetobacter bacteria. The recent outbreak of BSE in the UK is thought to be the result of inadvertent contamination of cattle's winter feeds with acinetobacter bacteria.

Official sources find problems with this theory, (see www.bse.org), claiming that proteins in the bacteria would be denatured by the heat pasteurisation process. However, they have yet to come up with a convincing explanation for their assertion that prions, which are after all protein fragments, would not be damaged by this process. It seems more likely that prions are symptomatic of the brain damage than its cause.


BIBLIOGRAPHY

http://www.stats.org/newsletters/9806/madcow.htm
http://www.bse.org.uk/report/volume2/chaptea4.htm
Professor Alan Ebringer - King's College London