Mad Cow Diseases Still
Baffle Scientists - Jump Species

By Maggie Fox
Health and Science Correspondent

Note - As I and others have been saying for years, prion diseases are undoubtedly spreading through the environment and now infect scores of species of animals. As mad deer drop dead, for example, and are consumed, prions from that animal can be eaten and carried off by all the animals and insects which feed on the carcass. The entire food chain can be impacted. Think about it. This story is one of several which are now beginning to openly state prions diseases can and do 'jump species.' Please also read carefully the stories in: 'Who Is Watching The Spread Of Prions.' -ed
WASHINGTON (Reuters) - Mad cow disease, which officials say has been found for the first time in the United States, still mystifies scientists because it is not caused by a virus, bacteria or other microbes, does not alert the immune system and can jump from species to species.
U.S. Agriculture Secretary Ann Veneman said the disease, formally known as bovine spongiform encephalopathy, or BSE, had been found in a single Holstein cow in Washington state.
"Even though the risk to human health is minimal, based on evidence, we will take all appropriate actions out of an abundance of caution," Veneman told reporters on Tuesday.
People can get a form of Creutzfeldt-Jakob disease known as vCJD from eating beef products infected by BSE. At least 137 people have died of vCJD, all linked to eating beef or to having received blood or tissue transplants from vCJD patients.
"In contrast to the traditional forms of CJD, vCJD has affected younger patients (average age 29 years, as opposed to 65 years for CJD), has a relatively longer duration of illness (median of 14 months as opposed to 4.5 months) and is strongly linked to exposure ... to BSE," the World Health Organization said in a statement.
BSE and CJD are members of a class of diseases called transmissible spongiform encephalopathies, or TSEs. They are believed to be caused by misfolded proteins called prions.
TSEs affect cats, mink, elk, deer, cattle, sheep and a range of other animals. Rabbits, horses and dogs seem to be resistant but it is not clear why.
TSEs can be passed on in food. Cattle are believed to have become infected with BSE when they were fed the rendered remains of sheep, which have their own TSE called scrapie.
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.


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