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Mad cow disease: Is it still around?


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Mad cow disease (also known as Bovine spongiform encephalopathy [bSE]) is a neurodegenerative, fatal affliction of cows. It’s caused by prions, which are proteins that are normally present in cows, but they have been mis-folded. Think of a paper clip as a prion, and its unwound form as a straight strip of metal is the original protein. The mishapen prions can also induce other normal proteins around them to become prions.


Prions are not alive – they are errant proteins produced in an animal, much like cancer cells are regular human cells gone wrong.




Seems like mad cow is going to stay for a while


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The naturally occurring human version of this affliction is Creutzfeldt-Jacob disease. It pops up naturally in human populations and has been transferred naturally by infection from the practice of cannibalism as curu. The disease is called scrapie in sheep and has been found in most mammals where it has been looked for, including deer and squirrels. The misfolded proteins can be transferred to the same species relatively easily and this has occurred in humans when it was found that typical surgical sterilization techniques failed to eradicate the proteins on neurosurgical instruments, and in cows when they were fed cow chow that was enriched with protein made from downer cows. Cross species infection is relatively rare because of the slight differences in the neuron membrane protein involved so that the possibility of humans contracting mad cow disease is zero if one doesn't eat meat from an infected animal. SM

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I know there was a article publised in the lancet a few years ago that looked at incubation periods of kuru, suggesting that prion diseases in humans may have an incubation period of 50 years or more! If this is the case, a CJD epidemic could be just waiing to happen....

Collinge et al (2006) Kuru in the 21st century—an acquired human prion disease with very long incubation periods The Lancet, Volume 367, Issue 9528, 24 June 2006-30 June 2006, Page 2034, clear.gifdoi:10.1016/S0140-6736(06)68930-7

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JohnG. I read the article and don't think it suggests an epidemic. More likely a few more bovine spongiform encephalopathy (BSE) cases over the years. This is an interesting study and the authors discussed several uncertainties regarding predicting from their data in some detail. A newer study by one of the authors has refined and broadened some of the findings, but conclude-


"Our data lend considerable support to the hypothesis that genetic susceptibility in addition to PRNP codon 129 genotype has contributed significantly to the outbreak of vCJD to date. Whether these effects are on the incubation period rather than susceptibility, such that further waves of BSE-associated prion disease with longer incubation periods might occur in the years ahead and be associated with different genotypes at many risk loci, is unknown."




Edited by SMF
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I agree, it remains unknown. However, the possibility remains that more than 10,000 people may be infected with the abnormal prion.




Then again other studies suggest the number may be considerably less




An interesting editorial on the subject can be found here



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