INDEPTH: MAD COW
BSE Mad Cow: FAQ
CBC News Online | From The National January 15, 2004
The National asked our viewers to send in questions about BSE, bovine spongiform encephalopathy, the proper name for mad cow disease. The answers are provided on Jan. 15, 2004 by CBC news staff and an expert in the field, Dr. Chris Clark, professor at the Western College of Veterinary Medicine at the University of Saskatchewan.
1. What causes mad cow disease? (Kevin Tisdall, Vancouver)
Reporter: Dan Bjarnason
The story of mad cow disease is in large measure a classic detective yarn. It began in England in 1984 when a cow developed strange symptoms and soon died. Then the bodies started to pile up, and scientists were soon chasing down clues. It took two years, to 1986, before the British made their first diagnosis of what is technically known as bovine spongiform encephalopathy. Eventually, almost five million cattle were slaughtered, but not before almost a million had made it into the food supply.
Initially the public was assured there was no danger to people, but soon a new strain of the disease was detected in humans and as many as 140 people have died. BSE gets its scientific name from the microscopic holes in the brains of affected animals, giving the tissue a sponge-like appearance.
Mad cow disease is still full of mystery. BSE is but one of a group of brain diseases affecting various animals, such as chronic wasting disease in farmed elk and deer in North America. It's caused not by bacteria or viruses, but by rogue proteins called prions.
Tests for these diseases are essentially hunts for the presence of infectious prions. These tests are done on brain and spinal tissue of dead animals where prions are most highly concentrated. Mad cow disease starts when prions mutate. Even in their normal state, their function is a mystery. The mutated prions trigger a chain reaction, not fully understood, which eventually kills the original cell and then moves on to other cells. And the process begins all over again.
Holes form in the infected brain, crippling the affected animal and finally killing it. The only known source of mad cow disease is from feed already contaminated from another diseased animal.
The original source of BSE is believed to be feed containing tainted meat from sheep with a related disease called scrapie. The disease gets into the human food supply when an infected cow is slaughtered for meat. Mutated prions are treacherous creations. They are very hard to destroy, and once someone is infected, there is no treatment, no cure, and death is a certainty, and it can't even be diagnosed until after death has occurred. Tackling BSE is made particularly tricky by the fact that it has a long incubation period. Symptoms may not show up for at least three years and perhaps as long as eight.
2. If BSE-contaminated meat did make it into the food supply, what is the chance that a person consuming the meat would contract the human variant of the disease, and is the disease always fatal? (Cathy Miller, Saskatoon)
Dr. Chris Clark
The first thing we need to put into context is to understand that the infection is really restricted to certain tissues in the body. It's not a disease that's distributed sort of from one end of the animal to the other. In particular, the disease is really restricted to the brain and the spinal cord.
For a number of years now in Canada, that material has been removed from the carcass and does not actually end up on the table. So really I think people can be quite confident that eating meat is safe.
As regards the risk of transmissibility, what we do know from Great Britain is the first case of BSE was diagnosed in 1986 and there've been about 180,000 cases since then. However, prior to 1986, before the disease was first diagnosed, large numbers of animals, we believe, were infected with the disease. Those animals were slaughtered for human consumption and, at that time, we do know that the brain and the spinal cord was making its way through to the dinner table.
For that reason, a large proportion of the British population were probably exposed to BSE. Britain has a population of about 50 million people. I'm one of those people who during the early 1980s almost certainly ate the material. Since that time, there have only been about 140 cases of BSE, so what that does tell us is that the risk of transmission is, in fact, incredibly small. While the disease was certainly a terrible disaster for the family of those people affected, it really doesn't transmit very well to humans.
3. Is it fatal, though, if it does transmit?
Dr. Chris Clark
Absolutely, yes. Unfortunately all of these spongiform encephalopathies are universally fatal in all species.
4. One theory about how BSE came to Canada is through British feed contaminated with mad cow. Is this the case? Do we know how BSE came to Canada? (Jim Roll, Regina)
Reporter: Kelly Crowe
After years of insisting Canada is mad cow-free, officials are now forced to face a disturbing fact: mad cow disease slipped into the Canadian feed system at least six years ago and probably even before that.
Dr. William Houston was on the international team that reviewed Canada's investigation into the mad cow contamination.
"It's most likely to have occurred, my best guess is sometime in the early to mid-1990s," he says.
It was circulating in meat and bone meal, bits of dead cattle ground up into a protein supplement.
Before 1997, it was legal to feed this cattle meal back to cattle. That's how the infection spread. Now officials believe the Canadian infection started with a British cow, imported to North America and processed into feed without anyone realizing it was infected.
Dr. George Luterbach is on the government team trying to piece the puzzle together.
"The main hypothesis on the introduction of BSE into Canada would first be the import of U.K. animals in the 1980s or indirectly, if a U.K. animal was to have died of BSE in the United States and was imported with meat and bone meal imported from the U.S.A.," Luterbach says.
Before 1990, it was still legal to import cattle from Britain.
Between 1982 and 1990, Canadian farmers imported 182 British animals.
By 1990, the British epidemic was so serious that Canada banned all further British imports.
The ones that were already here were catalogued and watched, but there were no rules against processing them. And officials now believe 68 British animals went into the Canadian food or feed chain.
"There were 68 of these animals that had already died from various causes in Canada, not recognized to be BSE, and potentially they were the source of BSE entering into the Canadian feed system," Luterbach says.
Of those 68 animals, 58 came from British farms that had no mad cow disease. That's reassuring. But 10 came from farms in Britain that did have mad cow disease at some point.
Three British imports are especially interesting. They were members of the Salers breed – prize purebreds. They were born in Britain in 1986 at the same farm. It's assumed they all ate the same British feed. They came to Canada in 1987 together in the same shipment and went to three different Alberta farms. Two died and were processed into feed and food. Then the third one got mad cow disease. It was Canada's first case on this farm near Red Deer, Alta. That was 1993. Now, Dr. Houston says those two animals are the prime suspects for starting the Canadian infection.
"I think that's the highest likelihood. If I was a gambler, that's where I would put my dollar right now, that those two cattle were the most likely source of the introduction of the agent," Houston says.
Canadian officials won't go that far, but they do say one of those imported British animals in that original group of 68 is the most likely source. When they factored those British imports into their risk assessments, they determined Canada's risk of mad cow infection was "negligible." Now they know it has happened at least twice.
If the British imports are the source of the infection, that means there could have been a window where Canada was potentially exposed to BSE without any firewalls, before the feed ban in 1997, and before the change in butchering practices that happened just last year. It's a window of possible low-level exposure that could have lasted between four and 15 years. Testing didn't start until 1992, and then it was fewer at than 1,000 animals a year. Now they're testing more and they're finding more.
"I think one might argue that two animals in 13 million is a very small number," Luterbach says.
Investigators say they will never have the complete picture of what happened because they're piecing this mad cow puzzle together from old documents and fading memories.
5. What is the cost of testing a cow for BSE? (Keith Allred, Edmonton)
Dr. Chris Clark
At the moment we're not sure what the final cost is going to be, but as a rough ballpark, it looks like the price will be somewhere in the region of $50 to $60 to test an animal. The cost may change once we start testing, depending on the scale of testing.
6. Is that the right way to be spending money countering this?
Dr. Chris Clark
What people need to recognize is there's been a lot of debate about whether we should test every animal. I think people need to recognize that the cattle that we eat roughly fall into two populations. On one hand, we have the young animals from the feedlots, and, on the other hand, we have the cull cows, which are typically the parents of those animals.
The younger animals are typically less than 18 months of age and, consequently, are actually entirely safe. BSE really doesn't occur in animals until at least 30 months of age. There's no evidence of disease. Science has shown that there's really no infectivity in those animals. So I think testing those young animals would really be quite worthless. If we're going to talk about testing, we need to look at the older animals, those in excess of 30 months of age.
7. My family and I were wondering if the spread of BSE to humans could be prevented by cooking beef to a certain temperature. (Martha Moore, Manotick, Ont.)
Dr. Chris Clark
The steak that you eat on the table really will be free of BSE. As to whether cooking helps, the whole problem with the spread of BSE was the BSE agent, the prion, was actually able to survive the rendering process. Rendering basically involves pressure-cooking the tissues in order to produce the meat and bone meal. So the strange thing about these prions that makes them different from viruses and bacteria is they don't break down with temperature. So cooking would not protect you, but just to reiterate again, the steak will be free of BSE.
8. What are the often-referred-to "rendering plants"? (Lila Rauh, B.C.)
Reporter: Joan Leishman
It may surprise you, but only about a half of any slaughtered animal will end up on supermarket shelves.
The other half, the bones, blood, hooves and guts ends up here. Getting rid of this stuff is big business worth $400 million a year and it keeps 2½ million tonnes of slaughterhouse waste out of our landfills.
What's done with it is a process called rendering. The material is crushed up, put in a sort of pressure cooker, and boiled down. It's cattle brains, spinal cords, the lymph and nervous systems that contain the mutated prion thought to cause mad cow disease. This material continues to be rendered today. Keeping it out of the rendering process is challenging, says Steven Leeson, head of the Department of Animal and Poultry Sciences at the University of Guelph. "It would be exceptionally difficult to separate that out. I don't know any country in the world that requires that sort of separation."
Once rendered, the material is separated into a powdered protein and a fatty residue. The fat is used to make cosmetics, pharmaceuticals, and even candies like gummy bears. The powdered protein is mixed into animal and pet foods, and it's thought that cattle meal contaminated with mutated prions is what caused the BSE case in Canada.
To prevent exactly that in 1997, Ottawa ruled that cattle could no longer be given food made from rendered cattle remains. And recently, Canadian renderers made another change, processing only one type of animal at a time, another step to minimize the risk of cattle being fed back to cattle. But what about other things that contain rendered byproducts, like the gummy bears? Could they possibly contain the protein linked to mad cow?
"Consumers hear about the problem, so think there's a risk there. The risk is, you know, absolutely infinitesimal as it stands at the moment. Is there 100 per cent guarantee? No, there's no 100 per cent guarantee with anything these days," Leeson says.
So far, all of Canada's 27 rendering plants are still in business, and only one is turning away cattle carcasses. But it's an industry bracing for the worst as fears grow that demand for some of its rendered protein byproducts could vanish.
9. Could consuming dairy products such as milk and cheese pose a potential health concern? Can BSE be contracted by consuming dairy products? (Jamal Ahmed, Toronto)
Dr. Chris Clark
This was actually a very big topic in Britain because I don't think a lot of people realized that BSE in Great Britain was really a disease that affected dairy cattle. In fact, probably greater than 85 per cent of cases in Great Britain occurred in dairy cows, so there was a lot of research early on looking at this issue. It's been tested extensively and they've never been able to find any infectivity whatsoever in milk. Milk is one of those tissues that we consider to be extremely safe for the risk of transmission.
10. Great Britain has a lot of experience with BSE, and I'm curious to know whether they have changed the way they do things and whether what they're doing is different from the way we do things and how much should we be learning from their experience before it's too late? (Brian Dench, Peterborough, Ont.)
Reporter: Don Murray
Eight years ago, Britain's countryside was a dead zone. A deadly variant of BSE had been found in humans. The disease was rife in British cattle. Tens of thousands of cases had been diagnosed in previous years. This was a crisis, and the crisis solution was mass slaughter. Half the British herd, 4.7 million cows, were killed and burned. For British farmers, the BSE crisis was a major trauma. And even now, eight years on, its effects are still being felt. David Christianson had just become a partner on his father's dairy farm near Oxford. Seventy cows on their farm were found to have BSE in a herd of 450. It was a serious economic blow, but one cushioned by compensation for each slaughtered animal from Britain and from Europe.
"We were compensated for the animals we lost, but they only compensated you for the value of the animal, not the loss of income that came from the animal. So with the cows, we lost the milk flow that we were getting, we lost the calving that was coming from those cows and that was a significant amount of money. So it made quite a dent," Christianson says.
The impact on British beef cattle farmers was far greater. Britain became a pariah country, its beef cattle unexportable. The legal ban on exports to Europe lasted five years. Even now with the ban lifted, for farmers like Chris Lewis, the export market remains closed.
"We haven't exported a thing since the day that this started in 1996, and so the whole of that market's gone. Now, they have replaced their beef supplies from elsewhere. It's going to take one heck of a time before we can establish that market again," Lewis says.
Inside Britain, there were stringent new rules.
"Between farms and between markets and if it goes for slaughter, the passport goes with it," Lewis says.
All British cows now have passports that trace every move they make from farm to farm to slaughterhouse. Their numbers are stapled to their ears.
"An animal cannot by law move off this farm without one of these, and if the police stop you and want your documents, it is exactly the same as you going intercontinental. You wouldn't get very far without a passport, we hope," Lewis says.
The passports were only part of the new regime. All cows over 30 months that are slaughtered are then burned. None enter the food chain. Each year, half a million cows are tested for BSE. There are still cases, 500 last year, but only 82 in the past four years from cows born after 1996. Britain banned feed from animal carcasses for cows, a probable source of infection, 16 years ago. Europe only got around to it three years ago. British officials believe that some of the new cases may be imported from Europe.
"One of the possible explanations for the reason that we're getting cases in animals born after August 1996 is that there were very low levels of infectivity, maybe even in imported feed from these other countries," says Dr. Peter Nash of the British Dept. for Environment, Food and Rural Affairs.
Eight years on, despite new BSE cases every year, all is calm in the countryside. British dairy and beef farmers thrive. The number of deaths from variant CJD, the human strain of BSE, is just 143. Beef consumption is so great, the country hasn't enough. The once powerful exporter now imports one third of the beef its people eat.
11. Regarding the producers suffering from the effects of the mad cow scare, why are the prices of beef in stores barely changing while producers get so little for the cattle they sell? (Cheri Chartier, St. Lazare, Man.)
Kimberlee McKinnon (Canadian Council of Grocery Distributors)
The price of beef has gone down over the last six months, and it was just starting to go back up towards the months of November and December when this second crisis hit. So what will unfold is if the price is going to go up or down, it will happen in the next six to eight weeks because we purchase beef products about six to eight weeks in advance.
12. Dr. Chris Clark, what's the most common question you're asked about mad cow?
I think a lot of people want to know what's different about Canada compared to my experiences in Great Britain, and I think, really, the answer to that is that when we found BSE last summer in Canada, we had 17 years' worth of experience of dealing with the disease in Great Britain to rely on, and, in fact, Canada had already learned a the lot of lessons from Great Britain. In particular, we were already removing the high-risk materials from the cow carcass before it went for human consumption, we banned the feeding of rendered meat and bone meal, and we also had that cattle identification program in place, and those three things really meant we were prepared when we found that case.
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