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The Science Of Mad Cow Disease

By CBSNews.com staff CBSNews.com staff

January 31, 2001 / 12:38 PM EST / CBS

In the last report in a three-part series, CBS News Correspondent Wyatt Andrews reports on the mysterious agent that causes mad cow disease, the prion, and steps scientists are taking to develop a test for it.

As if mad cow disease isn't frightening enough, the cause is the stuff of science fiction. The cause is 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" in which the brain is wasting away, said Prusiner,

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In the 1950s a disease similar to mad cow 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, it seems, comes from healthy cows eating the remains of infected cows in feed. Somehow, the infectious prions jump to humans in 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 Galo 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. "We have to be concerned enough that we should be prepared, but I can't answer you that we should be scared," he said.

There are some reasons not to be alarmed by prion diseases. They are not thought to be contagious person-to-person, and despite the rising mad cow numbers in Europe, that disease is still very rare. However, of all the creatures found with 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 thousands of human carriers are incubating mad cow prions now, but don't know.

When asked if, in his darkest moment he thought that this is 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 is hard to detect, impossible to treat, and its true reach into human beings is unknown.

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