CJD in the USA Dec 26, 2003 1:31:28 GMT -5
Post by Big Bunny on Dec 26, 2003 1:31:28 GMT -5
Rendering or processing food can destroy the prions, but only with difficulty. Just cooking will not do the trick.
Experts were not available to comment on the case of the U.S. cow on Tuesday evening, but there is disagreement on just which beef products may carry the infectious prions that cause the disease. British officials say milk cannot transmit the agent, but there is strong evidence that nerve tissue and other cattle parts ground up for some products may carry it.
A recent Swiss study suggested that, in theory, muscle tissue -- which would include steaks -- could carry the agent.
No one knows how much a person has to eat to become infected.
Because the misfolded proteins, or prions, believed to cause the TSEs occur naturally in the body, they do not alert the immune system as a virus or bacteria would to prompt a fight against the disease.
Recent research suggests the "bad" prions can cause others to go bad simply by touching them.
Proteins are made by cells following instructions laid out in the genes. But like a cardboard box, a protein must be folded to function and they sometimes get folded into the wrong shape. Usually a cell will recognize this and cause it to be broken up.
But Susan Lindquist of the Whitehead Institute at the Massachusetts Institute of Technology and colleagues found in late 2002 that this does not always happen. They discovered that if the misfolded prions are not broken up quickly enough, they accumulate and alter the cell's metabolism, killing it.
In the brain this kills neurons. When the neurons die they break apart, releasing more prions into the system.
There is a genetic susceptibility to TSEs. For example, CJD occurs sporadically, or randomly, in about one in 1 million people. There is a gene mutation that runs in families and causes 5 percent to 10 percent of cases of CJD.
CJD, which is incurable and always fatal, can also be passed on by tissue transplants and, in theory, in blood.
This last comment about transmission by blood has in fact been confirmed as another practical method of transmission: