Can Mad Cow Disease Reach Our Shores? (Part 3)

As if mad cow disease isn't frightening enough, the cause is the stuff of science fiction--a mutant protein that kills the brain. It's called a prion and scientists haven't seen anything like it since Louis Pasteur found germs.


"I describe the prion as a completely new infectious particle. It's not a virus, not a bacterium, not a fungus. Different," said Dr. Stanley Prusiner.


Prusiner, of the University of California, San Francisco, won the Nobel prize in medicine for discovering the prion. It's a natural protein in mammals that can mysteriously deform itself, replicate, and concentrate in the brain.


"The end result of this accumulation of prions in the brain are these big holes in the brain. A Swiss cheese appearance" that reveals that the brain is wasting away, said Prusiner,


In the 1950s a similar disease was found in Papua New Guinea. A tribe there got a brain-wasting disease called kuru after eating the prion-infected brains of dead relatives in a religious ritual. Cannibalism is the link. Mad cow disease, it seems, is caused by healthy cows eating the remains of infected cows in feed. And then, somehow, the infectious prions jump to humans who eat beef.


The outbreak in Europe has launched a scientific race to find a blood test for prions. The idea is, if you can find the infection in cows, you can prevent it in people.


"We can take all the animals that are positive, that are infected with prions, if your test is good enough, and we can keep all these animals out of the human food chain," said Prusiner.


Also working on a blood test is Dr. Robert Gallo at the University of Maryland. Gallo, the same man who helped discover HIV, says there's nothing as indestructible as a prion. If it was in your meat, Gallo says, it could not be cooked out.


Gallo is unsure about the threat from mad cow disease. Although he thinks we have to be concerned enough to be prepared, he's not sure or not if we should be scared.


There are some reasons to not be alarmed by prion diseases. They are not thought to be able to pass from person to person, and despite the rising mad cow disease numbers in Europe, it is still very rare. However, of all the creatures found to have a prion disease--cows, sheep, elk, human beings--not a single victim has ever recovered.


And here is the wild card. Remember that cannibal tribe? Some did not get sick for 40 years. To scientists, that means a small, but real, risk that thousands of human carriers are incubating mad cow prions now, but don't know it.


When asked if, in his darkest moment, he thought that this could be the plague of the 21st century, Prusiner said, "I don't need a dark moment to wonder if that's the case, because everybody's wondering that--not just me."


Prusiner is certain someone will find a medicine to neutralize prions. Right now, mad cow disease is hard to detect, it's impossible to treat, and its true reach into human beings is unknown.



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  • CBSNews.com staff CBSNews.com staff

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