Why are cows going mad?
BSE & Creutzfeldt-Jakob Disease

 

Bovine Spongiform Encephalopathy (BSE)

Bovine Spongiform Encephalopathy (BSE) is a fancy name for a certain type of neurological disorder found in cattle. "Bovine" refers to cows, "encephalopathy" refers to the brain and "spongiform" refers to the spongy appearance of the brain upon autopsy. The recent outbreak in the UK may have begun because cattle were being fed scrapie-containing sheep meal. Scrapie is a similar neurodegenerative disease found in sheep. The disease spread rapidly because of the common practice of feeding cattle meal to cattle. This practice has been prohibited in the UK as a result. France, Germany, Ireland, Portugal, Spain and Switzerland have each had cases of BSE.

2003 First case of BSE in the US (Washington State). Read CDC Report

Both scrapie and BSE are believed to be caused by prions (see below).

The BSE prions are most likely to be in beef products derived from the brain or spinal cord. Solid muscle meat (e.g. steak) is less likely to contain BSE prions than ground beef (which contains meat from various parts of the animal and may be more likely to have come in contact with tissue from the brain and spinal cord).

What is a prion?

Proteins are the workhorses of the human body. They are long strings of amino acids that have been folded, knotted up or otherwise tied together and their 3 dimensional structure determines what they do. If this structure changes, then they can easily lose the ability to do their natural job in the cell. A prion is a protein that is infectious.

How can a protein be infectious, you ask? The prion that causes BSE is a mutant of a normal mammalian brain protein. When the mutant comes in contact with the normal protein, it can "tweek it"...turning it into the mutant form. It is thought that the body can't recycle this mutant protein...and so it builds up, clumps together and is eventually destructive to the brain and nerves. Unfortunately, only a very small amount of prion is apparently needed to cause infection and they are not inactivated by cooking or even traditional sterilization procedures like pasteurization.

For many years, scientists around the world "poo-pooed" the idea that proteins could cause disease. Until very recently, it was believed that an organism had to have nucleic acid (like DNA) to cause an infection. Thanks to a man named Stan Prusiner, who persisted in the face of extreme skepticism, we understand how BSE and CJD can be transmitted (and stopped!). He received the Nobel Prize in Medicine in 1997 for his work: S. Prusiner's Nobel lecture - 1997

NEWS - May, 2003: A case of BSE in Canada. New Scientist Article for more information or CDC site

NEWS - December, 2003: A case of BSE in the U.S. Articles (also includes info on vCJD cases in the U.S.)

The mutant protein (prion) that causes BSE, in its normal form, may be important for storing memories in the mammalian brain (Nature News, Dec. 2003)

US FDA consumer BSE FAQ

 

Creutzfeldt-Jakob Disease (CJD)

CJD is a fatal, degenerative disease with no cure. Mental deterioration, neuromuscular and sensory problems eventually lead to coma and death within a year of getting the first symptoms. It generally affects people over age 60. A small number of cases are hereditary. A larger number are sporadic (not linked to an infection or genetics). Some cases are the result of contaminated surgical instruments or from surgical procedures involving contaminated tissue (esp. cornea or dura mater (lining of the brain) transplants). Some cases have arisen from natural human growth hormone therapy (using genetically engineered human growth hormone eliminates this risk).

 

variant Creutzfeldt-Jakob Disease (vCJD)

This is a type of CJD that appears to be caused by the same prion that causes BSE in cattle. Thus, it is believed that people with this form of CJD contracted it by eating meat that was infected with the BSE prion. So far there have been 113 deaths in the UK, 3 in France and 1 in Ireland. The disease is similar to inherited or sporadic CJD, but the disease progresses more rapidly and happens to people at a much younger age. The incubation period between infection and showing symptoms may be very long (up to 10 years).

vCJD and blood transfusions

There have been no documented cases of vCJD from blood transfusion, but there is a theoretical risk. Precautions are now being taken in the UK to prevent transmission through transfusion. The US will not accept blood from donors that have lived in France for 5 years or more between 1980 and the present or have visited or lived in Britain for a total of 3 months or more between 1980 and 1996. Canada will not accept blood from a donor that has spent 6 months or more in the UK or France during 1980 to 1996. For more info see: new FDA guidelines 5/2002


Useful sites:


Excellent site on BSE and CJD from New Scientist - information and news
Excellent FAQ from New Scientist
CDC primer on BSE and vCJD
US Natl. Library of Medicine - CJD primer
BSE primer from WHO
CJD Foundation
"mad-cow.org" - confusing to navigate


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