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Risk of mad cow disease in humans and in animals making its way to the Americas

December 7, 2001 National Public Radio (NPR): Talk of the Nation/Science Friday
IRA FLATOW, host:

Welcome back to TALK OF THE NATION/SCIENCE FRIDAY. I'm Ira Flatow.

And for the rest of the hour, mad cow disease. Earlier this month, authorities in France reported the fifth case of the human form of mad cow disease in that country. In Japan comes news that a third cow in that country has come down with the disease. And these reports from around the world come at the same time as a new report from the Harvard Center for Risk Analysis. The center looked at what would happen if mad cow disease was introduced here in the United States. And that report is a statistical analysis, and it concluded there would be little chance that the disease would be a serious threat to public health or to the human cattle herd. Others take issue with the findings.

And for the rest of the hour, we'll be talking about that report and the possibility that mad cow might show up; what action would follow, should a case appear. So if you have a question about mad cow disease showing up on this continent, give us a call. Our number is 1 (800) 989-8255, 1 (800) 989-TALK. Now let me introduce my guests. George Gray is the acting director of the Harvard Center for Risk Analysis in the School of Public Health at Harvard. He joins us from the studios of WBUR in Boston.

Thanks for being with us.

Dr. GEORGE GRAY (Director, Harvard Center for Risk Analysis): Happy to be here. How are you, Ira?

FLATOW: You're welcome.

Linda Detwiler is a senior staff veterinarian at the Animal and Plant Health Inspection Service of the US Department of Agriculture. And she joins us by phone from her office in Robbinsville, New Jersey.

Welcome back to SCIENCE FRIDAY, Dr. Detwiler.

Dr. LINDA DETWILER (Animal and Plant Health Inspection Service): Yeah. Good afternoon.

FLATOW: Good afternoon.

Dr. Peter Lurie is the deputy director of Public Citizen's Health Research Group, and he joins us by phone from his office in Washington.

Thank you for being with us.

Dr. PETER LURIE (Deputy Director, Public Citizen's Health Research Group): It's a pleasure.

FLATOW: Let's talk about mad cow disease. George Gray, Japan had its first case of mad cow disease this past September. And, of course, that makes us wonder, 'Can it happen here?' George Gray.

Dr. GRAY: Well, Ira, it can happen here. There is no way that we can say that there is zero risk. There is a chance that BSE could occur here. The risk is very, very small. [Two of the most prominent mad cow researchers in the US disagree. Because of the likely occurence of spontaneous cases in cattle populations, both the late Dr CJ Gibbs, who chaired the World Health Organization\'s investigation into mad cow disease, and Dr. Stanley Prusiner, who won the 1997 Nobel prize in Medicine for his discovery of prions, both have been quoted as saying we must already have at least a rare form of mad cow disease already in this country--BSE coordinator] But what our report showed is that even if it were introduced to this country, it's not going to spread. And that's because of a variety of programs that have been put in place by the government, by industry, that essentially keep a sick cow from making other cows sick. So we certainly cannot say the disease won't occur here, but what we can say is that if it does, it's not going to be a major public health or animal health problem.

FLATOW: Well, why would it not spread like it did, for example, in England or other places where it did catch on?

Dr. GRAY: Well, we've actually been very lucky in that we've been able to learn lessons from the unfortunate situation that happened in England. And one of the things that we've learned is how BSE apparently spreads. It's not a really contagious disease, the kind that you think of where one animal easily gives it to another. [In the US, however, we have a mad cow-like disease among wild deer and elk called Chronic Wasting Disease that does seem to be able to be spread by casual contact between animals--BSE coordinator] As far as we know in BSE, the disease is only contained in a few parts of a sick animal. It's in its brain, in its spinal cord and some other tissues of its central nervous system. If you can prevent those parts of an animal from getting to other animals, you can prevent the spread of the disease.

Here in the United States, the most important thing we have for stopping the spread of the disease is a ban that was put in place by the Food and Drug Administration back in 1997 on practices that could spread those parts from a sick cow to other cows. Now we know that that system doesn't work perfectly, and we know that everybody's not doing the best job they could complying with those rules. But even with incomplete compliance, our study shows that the disease can't catch hold in the United States.

FLATOW: Mm-hmm.

How do you react to that, Peter Lurie?

Dr. LURIE: Well, it once again shows that the Harvard Center for Risk Analysis is exaggerating, I think, even the findings of their own report. Dr. Gray just said it won't spread. But that doesn't seem like a fair statement because even their report shows examples of some limited spread if the disease were to begin in this country. So I don't think that's true.

The Harvard--we need to know who's funding the study, who's paying for the study as well. The Harvard Center for Risk Analysis has been funded by over 100 major corporations and associations, including the National Food Processors Association, which would have an interest in some of the outcomes of this. And Dr. Gray himself has been in the newspapers on numerous occasions, going back for over a year, saying that his results were preliminary--no different than they are now, I might point out, but preliminary--and yet, injecting his points of view, even though the study was incomplete, saying there would be no problem. I really think that's inappropriate. And the funding of the Harvard Center for Risk Analysis, which has customarily produced results favorable to its funders, favorable to the tobacco industry, favorable to the cell phone industry, favorable to the chemical industry, really, I think, demands a second look before we can just buy the assumptions that they're making.

FLATOW: George Gray? A reaction?

Dr. GRAY: Sure. I think that we are very straightforward about our sources of funding. This particular study was funded by the United States Department of Agriculture, and we report that, as well as our other sources of funding, from the government, from industry and from foundations in our press releases, on our Web sites. We're very clear about that. I think that that still doesn't take away from the fact that we've conducted a very careful study, and that study shows that BSE can spread. And we're very clear about that. But that it doesn't spread enough to cause more disease. We could never have an epidemic.

FLATOW: Mm-hmm.

Dr. GRAY: And we're taking sort of a public health view of this. We're asking the question not can it occur, because we certainly cannot rule that out. The question is: If it got here, could it become a serious problem? Would it spread? Would we end up like the UK, where they had thousands of cases of BSE a month?

FLATOW: Mm-hmm. Well...

Dr. GRAY: And the answer we find is no.

FLATOW: ...Linda Detwiler, let's talk about how mad cow disease does spread from animal to animal and why your study, in collaboration with Harvard, would say that it's not really going to spread.

Dr. DETWILER: Well, the way the disease is spread, the primary if not sole route, is when you have an animal that's sick with the disease, that animal is slaughtered, rendered and then fed back to cattle. There's no scientific evidence at all that the disease spreads from cow to cow. And I think that's important for the whole world. And I think that not only the United States, but also other countries of Europe and other countries in the world have learned from the UK. They were unfortunate. They had to face a new disease in 1986, for the first time, not knowing any of this information on transmission. So I think a good example is even Europe--that no country is predicted to have anywhere near the epidemic that the United Kingdom is. So if you look at the US, that our risk factors are lower and, you know, people have now, in the last week or so, said that about Harvard being suspect. But this only corroborates the same findings that the European Union found with the US a year ago.

FLATOW: Mm-hmm.

Dr. DETWILER: European Union reported that the US, given the risk factors, was unlikely to have BSE, but it couldn't be fully excluded. And for us, that's saying the same thing, that they're finding the same thing. And two different bodies, one the European Union and this, Harvard, I think the important thing for the United States Department of Agriculture with Harvard--it's provided us with a model to look at specific pathways that, if the agent is in the US, what further actions we can take to reduce either a spread within the animal population or what's presented for humans. And that's exactly what the department's supposed to do.

FLATOW: How would we know and how do we know whether or not it has spread to the animals here?

Dr. DETWILER: By our testing program. And in the US, what we test is we test the highest-risk categories. And again, Europe came out with another report to just really emphasize the importance of testing neurologically ill animals, as well as what they call 'fallen stock,' what we call 'downer cows.' And that's where we're gearing our surveillance. And last Friday, the secretary of Agriculture announced that we would be doubling again, between the year 2001 to 2002, the number of animals sampled, up to now a total of 12,500 for the year 2002.

FLATOW: And how many animals are there in the country?

Dr. DETWILER: Well, there's about a hundred million total cattle in the population. About 35 to 40 million of those are adults. They think that, again, most importantly are the high-risk population would be dairy animals, and there are about nine million...

FLATOW: Mm-hmm.

Dr. DETWILER: ...dairy animals in the US.

FLATOW: Peter Lurie, any problem with the inspections going on here?

Dr. LURIE: Well, Linda and I have disagreed about this because we've done a report on the surveillance system the United States has in place. I actually think that the numbers that they're doing, at least when increased to 12,500, probably is about a reasonable number to do. After that, you start doing lots of testing for very little additional information, so I agree with that part. But what our analysis showed is that there's enormous geographic variation in the ways in which the testing is being applied. We found, looking at dairy cattle, the most at-risk category, as Linda said, a 600-fold difference between the highest rate by state and the lowest rate by state. And so we think that testing more up to the point that they're now proposing is good. But if you want to be most effective, you need to spread it around the country, much more uniformly than has so far been the case.

Dr. LURIE: Now I think that--and you made the point earlier on that this is a statistical or computer model. And I think that's exactly right. That's important to remember. There was no testing of humans. This is Dr. Gray's study, of course. No testing of cows, no testing of feed, no testing of products that might contain animals parts. And that doesn't mean that--that doesn't make the study illegitimate, of course. It just means that we need to keep that in mind when we're doing this.

But it's also important to remember that certain whole categories were excluded from the study. In particular, as far as I can tell from Dr. Gray's very extensive 500-page report, there is much concern about cows that might have BSE entering the country, but I don't see anything about the import of meat and bone meal, the feed that has been implicated in Britain. I don't see anything about the import of that, and I'd be worried, frankly, much more about improperly packaged or a bag entering the country than I would be about, you know, a large cow.

There's also no attention to the entry of the agent into the country through FDA-regulated materials like dietary supplements, which could, without very little--with much difficulty, if someone was so inclined, actually contain a crushed-up cow brain, even from Britain, in the worst-case circumstance, and actually be imported into this country because the dietary supplement laws in this country have been thoroughly mangled by the Congress back in 1994. There's also no discussion of vaccines and blood.

That's not, per se, a criticism of Dr. Gray's work. He is restricted to cows. But we need to remember that.

FLATOW: Mm-hmm. Dr. Detwiler, how do you react to those criticisms?

Dr. DETWILER: Well, I'll react to what the Department of Ag covers. How's that? And the meat and bone meal, too, is an issue that we're concerned about. I mean, we've put restrictions on in 1989 from countries with BSE; in '97, all of Europe. They've been continually looked at. We've done a trace active meat and bone meal imports, non-ruminant, of what was coming into the country during the '90s from countries in Europe and found that these importations were of pig material, mostly underskin, for a protein binder. Also some chicken material; but again, in small amounts. And I think the reason this is--and not to say that we shouldn't be vigilant at our ports or what not--if you look at the US, the same thing that makes, you know, these large cattle populations, large pig populations, large chicken that we have here, we produce a lot of our own meat and bone meal. The other thing we produce, a lot of soybean. So economically, you know, there's not incentive. That helps us.

FLATOW: But why not just then ban all animal feed that has animal protein or made from other animals and just use, you know, vegetables like soybeans?

Dr. DETWILER: Well, there's some animals that are omnivores or carnivores, like cats and what not, so you would have some health effects there. [Cows, of course, are herbivores though--BSE coordinator] And Europe is finding that out in some of the things. The other is that you have a disposal problem, that you have then this waste product, and if there's a way to recycle this animal protein back to species that does do well on this type of animal protein, that that's a good thing to do vs. trying to incinerate it, landfill it, etc. We also know that when they try to give BSE orally to pigs and chickens--All right?--they were not able to pass the disease. [Actually if one looks, for example, at last month's Journal of Virology, there's an article about such so-called "bvlind passages" where the intermediary animal (in this case perhaps the pig or chicken) may not come down with the disease but could still pass along the infection. Of course we splaughter poultry and swine at such a young age in thsi country that it's possible that pre-clinical cases may pop up--infected and potentially infectious animals who just haven't started showing symptoms of the disease--BSE coordinator] there may be pAnd better yet is that there was no residual infectivity in the body, so that--it's not like the agent stayed. They didn't get sick. And then if they--you know, the tissues were taken and then re-exposed, that they would pass the infectivity on. So I think the world is looking, and even Europe is looking, going back, is once they clean their feed systems out and get the agent out, that someday, they might be able to go back and use this animal protein, which is a good source of protein, in a species where it would be of value nutritionally. [Why is the USDA so wed to this animal cannibalism. Europe has banned the feeding of all animals to livestock--we should do the same--BSE coordinator]

FLATOW: Mm-hmm. Peter Lurie, any reaction?

Dr. LURIE: Well, you know, one of the concerns is that through no fault of its own, USDA is a little bit behind the eight ball in the sense that there will always be new countries, I think--at least up to a point; hopefully not us--that end up developing BSE epidemics of greater or lesser size. And so what has happened is as the next country shows up with BSE--most recently, Japan [By now, days later, Finland and Austrioa have fallen as well--BSE coordinator]--then the USDA quickly slaps a ban on the imports of cows or meat and bone meal from that country, and that's appropriate. But during the interim, it is possible that we could import meat and bone meal or indeed even cows from those countries, and, you know, before we learn that they, in fact, have an epidemic. And that is not, again, per se, a criticism of USDA, unless we're moving to a place where we would import nothing. And I'm not recommending that. But it is the kind of humility that I think we need to bring to bear on this debate, rather than somewhat exaggerated claims of safety that I think we've heard from Dr. Gray.

FLATOW: Well, and let me remind everybody that I'm Ira Flatow, and this is TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

Dr. Gray was not saying from--if I heard him correctly, that it's never going to show up here. He's just saying that from the way we are set up in this country to deal with it and how--the--statistically, from the patterns he has studied, it probably would die out quickly.

Dr. LURIE: No, absolutely. What he said, though--and I--you know, I wrote this down, he said, 'It won't spread.' And later on, he modified that, which I think was a good idea. But what is clear from his report--and I think this is one of the ways in which the report is really quite useful--is it identifies ways in which we can be still safer.

Well, the first thing, even before that, is it identifies that the current feeding ban is absolutely the key to the containment of any BSE epidemic, should one even begin in this country. And there, the issue becomes: What is the rate of compliance with the FDA ban? And he models this, appropriately, I think...

FLATOW: Remind us what that ban is.

Dr. LURIE: Well, it's a mammal-to-ruminant ban. [No, it's a rumunant to ruminant ban--meaning basically that you can't feed the remains of cows and sheep to other cows and sheep. You can still feed pig s to cows and cows to pigs, for example--BSE coordinator] So you can't feed cows to cows, most importantly. But other mammals also can't be fed to ruminants. And your question earlier was whether that ought to be extended to other animals--other mammals, and I think that's certainly something that should be considered. But this ban, which is the cornerstone of BSE protection in this country--and that's of protecting humans from the disease ultimately--is being enforced with much more force than before. For many years, I don't think FDA really was on the ball on this one.

But even today, at least at initial inspections, about 13 percent of the firms were found to be out of compliance. And that's very often because they weren't labeling the product properly or they don't have adequate systems to prevent co-mingling of the different kinds of feeds, which could result in cow parts being recycled and fed to other cows. And we already have an example from Texas from about a year ago in which there was an actual contamination of feed intended for cows that wound up with cow parts in it. The animals had to be destroyed, the ones that consumed it. And I--but--so it's not a theoretical possibility; it's very real.

Now Dr. Gray does the best he can with his computers to try and address that problem, but really, the whole BSE epidemic is about small-probability events that could be catastrophic. And I think that's what's so scary about all of this is things may be unlikely, but at least in some scenarios, if the unlikely thing happens, then truly terrible things can happen.

Dr. Gray's report, though, is--I must say, makes quite clear where we should be doing more, and there's some noise from USDA to address some of the things that he's addressed, especially improving compliance with the feed ban--that's FDA--but looking at this advanced meat recovery system, which we can talk about a little bit more in the future, and also he's highlighted, I think, in a way not previously highlighted, the problem of animals that die on the farm and subsequently get rendered and potentially enter the human food chain. I think that USDA is now starting to look at that, and I think that the report has been helpful in identifying that as a big problem.

FLATOW: Mm-hmm. Dr. Detwiler--well, let me ask Dr. Gray to react because I've used your name in vain a couple of times in the last--speaking for you. If you'd like to...

Dr. GRAY: But there's a...

FLATOW: ...change anything I've said, go ahead.

Dr. GRAY: Well, no, no, no. And Peter's been very kind to say good things about our report, so that I don't...

FLATOW: Yeah.

Dr. GRAY: ...things have been perfectly fair. I do want to say I think that it's true that our study is helpful in identifying things that can be done to improve even more the safety of the United States food supply and animal herd. And I think that it is a point that USDA--we can give these tools to the agencies, that they can use them and come up with the sort of things that make sense. Some of them, they can bypass a lot of these concerns even about the feed ban and just really cut that chance that a sick animal can make other animals sick.

FLATOW: All right. I'm--that music means I'm going to have to cut away and take a short break. It's good that everybody's trained like that when they hear the music. So don't go away. We'll come back and talk lots more about mad cow disease and go to the phones and take your questions, so stay with us.

(Soundbite of music)

FLATOW: I'm Ira Flatow, and this is TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

(Announcements)

FLATOW: You're listening to TALK OF THE NATION/SCIENCE FRIDAY. I'm Ira Flatow.

And we're talking this hour about mad cow disease with my guests, Dr. Peter Lurie, deputy director of Public Citizen's Health Research Group; George Gray, acting director of the Harvard Center for Risk Analysis; Dr. Linda Detwiler, senior staff veterinarian at the Animal and Plant Health Inspection Service of the US Department of Agriculture.

Our number 1 (800) 989-8255. Let's go to Daniel in Sacramento. Hi, Daniel.

DANIEL (Caller): Yes. Thank you for taking my call. I'm interested in an area that you've not yet touched on regarding the possibility and sources of human infection. And particularly, we should note that the disease in humans is very slow. It won't show up for a long time. Many of us could be infected, and we won't know about it for quite a while. And also, even though something is unlikely at any particular time, integrated over a long period, it becomes much more likely. And the--we should also remember that the infectious agent is a prion, and prions are extremely resistant. They're very hard to inactivate. And the two areas that I'm interested in is with regard to the food supply.

And there's many food items and additives that are derived from rendered cattle, often from the cheapest source of rendered cattle, which is usually South America, and the two major items that I'm interested in is something called flavoring and another item is gelatin, which are found in so many foods. And with regard to flavoring, let me just remind you there was this item in french fries that--a certain company in India produced french fries that were supposed to be vegetarian and were not and had these trace amounts of this flavoring which comes from rendered cattle. And it's actually in all the fast-food industry, you'll find it. And in many other canned foods, there's this item called flavoring, and often, it comes from rendered cattle. Please comment.

FLATOW: Yes, gentlemen, how do we know that we're not getting any infection coming through very common items like flavorings and gelatins that are processed foods?

Dr. GRAY: Well, maybe I...

FLATOW: Yes, go ahead. George.

Dr. GRAY: I'm sorry. I was going to say--this is George Gray.

FLATOW: Yes.

Dr. GRAY: I was just going to remind everyone that this concern that there has been apparently a link between BSE, which was always thought to be just an animal disease until 1996 when it was linked to a human disease that's called variant CJD, and there've been approximately 105 cases throughout Europe. It's only been seen in countries that have had BSE. We did look at the potential for the infectious agent, for BSE, to end up potentially reaching human food, and it happens at relatively low levels. And in our report, we detail the way in which that happens. But this specific question...

DANIEL: But how low is low, and over a long periods of time, this can be very important.

Dr. GRAY: Well, that's a good point. And all of our studies--we built a computer model to sort of predict what would happen if BSE were to get into the United States. And we ran that over 20 years, so we sort of looked to see over a long time what would happen.

DANIEL: That's barely the time for it to show up as a human disease. It often takes 30 years...

Dr. GRAY: We weren't looking at the potential for it to show up as a human disease. What we were worried about is whether people could be exposed to the parts of animals--remember, we've talked about this central nervous system and such--that can transmit the disease.

The thing that we've learned--tests have been done in the United Kingdom in which animals were deliberately given this disease and then tested to see which parts of them could transmit it. And, for example, BSE, as far as we know, isn't found in milk, it isn't found in meat, it isn't found in fat. It's found in these few nervous system tissues. So there was concern, and we look at the way in which that could spread.

DANIEL: But it is found in parts from rendered cattle.

Dr. DETWILER: But it's by contamination of the central nervous system tissue.

DANIEL: Right. But it's--rendered cattle is just--you know what rendered cattle is. It's just, you know, put in the vat and then made into whatever the company wants to make with it...


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