This is a partial transcript of Special Report with Brit Hume, Dec. 24, that has been edited for clarity.

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(BEGIN VIDEO CLIP)

ANN VENEMAN, U.S. SECRETARY OF AGRICULTURE: We know of no scientific evidence that would indicate that the muscle cuts of the meat from an infected cow would pose a risk to human health. So we believe we're going to take this recall action in an abundance of caution, but we do not believe there's a risk to human health in this particular situation.

(END VIDEO CLIP)

BRIT HUME, HOST: Despite those assurances, at least 11 countries, including the three largest customers, halted U.S. beef imports. Cattle futures plummeted on commodity markets and stocks in companies from McDonald's to the Outback Steak House took a hit. So, who's right here, American officials and the beef industry or the importers and investors?

For answers, we turn to a man who knows this subject as well as anyone. He is Dr. Paul Brown of the National Institute of Neurological Disorder and Stroke (search). Dr. Brown agreed to come in on his day off.

Nice to see you, sir.

DR. PAUL BROWN, NAT'L INSTIT. OF NEUROLOGICAL DISORDER & STROKE: Thank you.

HUME: Thank you very much for coming.

First of all, in the report that Molly Henneberg did, she described a process whereby an animal that's being slaughtered has the portions of its body that might be infected or affected by mad cow (search) disease removed. And that goes in one direction and the beef we might eat goes in the other. Is that the way it works?

BROWN: That's the way it works

HUME: And how — why should anybody ever be worried about mad cow disease reaching humans?

BROWN: Well, because scientific evidence is always imperfect and incomplete. And if you do five experiments and get one result, you might possibly get a different result if you did 500 experiments. And so, if we find that, for example, as we have, that there's no infectivity from muscle eat...

HUME: That's the stuff we eat. Steaks...

BROWN: That's right. On the basis of a number of experiments, it's always possible there might be just a smidgen of infectivity that would be detectable if we did 10 times that number of experiments.

HUME: So in other words, the experiments that we've done and tests that have been done on beef over the years, has indicated that this kind of infection does not seep into muscle tissue of the kind that we eat.

BROWN: That's correct.

HUME: But your view is that because you can't do absolutely — if you don't do 100 percent testing, you could never know. It could theoretically happen.

BROWN: Right. Right. And there's also a good, plausible explanation for the identity of the vehicle that has caused human infection. And that is historically, at least, a product called mechanically recovered meat (search). That is not the meat that's chopped off by hand by the butcher in the slaughterhouse. It's what's left after that has been removed.

HUME: You mean, meat that may cling to the bone?

BROWN: Correct. And historically what's happened there is that the carcass is put into a big press and is pressed. And historically again — and I keep saying historically because this has all changed now. In that press is the vertebral column.

HUME: And the vertebral column is where this disease would reside?

BROWN: That's correct. And in little ganglion that are around the vertebral column. They would have been part of mechanically recovered meat. Mechanically recovered meat was typically put in processed meat products...

HUME: Like, if I go by bologna at the supermarket.

BROWN: Exactly. Deli meats, bologna, beef stews, anything that is sort of precooked and not an intact piece of meat.

HUME: So you say it's all changed now?

BROWN: Yes. Mechanically recovered meat is on the way out. And they are now using, in preference, a gentler system of scraping the meat off the bones, rather than crushing.

HUME: Which would present less of an opportunity for the disease to seep out of the bone structure of the vertebra into the meat?

BROWN: Much less. Much less.

HUME: So, in this particular case, I guess the first question that we're all going to want the answer to is... it's hoped that this would be like the Canadian case, a kind of a one off, isolated incident; one animal infected or affected. How great do you think the chance of only one is?

BROWN: I think the chance is pretty good.

HUME: Really? Why do you say that?

BROWN: Well, because one, the experience of Canada. They haven't had a cluster of cases identified. And they're testing, testing, testing. The experience of other countries, such as Japan, which has its first case oh, about two years ago. After two years of total testing, they have a total of nine cases and tens of thousands of cattle.

So, I frankly, have to tell you that I was surprised that this happened. I have been saying for many years that I really didn't think BSE was going to show up in the U.S. So my ability to predict may be not as good as I had hoped.

HUME: And we need to know the history of this particular individual animal to know where it got it?

BROWN: Right. Exactly. Absolutely. Absolutely. If — just to give you an example. If it turned out, although people think it won't, that there's some kind of connection between this cow and the Canadian cow, I mean, that would — we could breathe a big sigh of relief. If it turns out that we could detect a bag of grain that was contaminated that had been by mistake imported from a country that now has BSE. But these are very difficult things to work out because they're four years old. One of the things...

HUME: You mean the animals are four years old?

BROWN: Yes. And so it...

HUME: And it takes some years for the thing to gestate, right?

BROWN: Yes. Exactly. The infection —this cow undoubtedly got infected about four years ago. The cow was 4 1/2 years old. Most BSE — the infection in BSE occurs within the first few months of life. So we're talking probably about an infection that occurred four years ago. And it's pretty darn hard to go back and say, “Yes, this bag came from Ireland,” for example.

HUME: You keep mentioning feed. I take it animals don't catch this from each other the way we would catch another kind of disease. This is transmitted in an indirect way. How?

BROWN: All the cases we know about so far, the most plausible explanation is they got infected from contaminated feed from this recycling that you talked about earlier in the show.

HUME: Because some parts of animals are recycled or they end up in animal feed?

BROWN: Exactly. There's no indication yet that one cow can give it to another cow.

HUME: Right. Well, that's reassuring, isn't it?

BROWN: And we hope that this...

HUME: One last quick question.

Will you be eating beef this holiday period?

BROWN: Well, yes, but not the on Christmas Day. We have turkey.

HUME: And already you were planning to, right?

BROWN: Yes. Right.

HUME: Dr. Brown, thank you so much. Merry Christmas to you.

BROWN: Thank you.

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