Are prions on your plate?
By Louise Brown

OTTAWA — Since the discovery of two cases of mad cow disease in Alberta, Canadians have been eating more, not less beef.

While beef exports have declined dramatically, Canadians have actually increased their beef consumption by 1.6 per cent over the past five years.

Dr. Aru Balachandran says that the risk facing Canadians from Mad Cow Disease is minimal.

Behind this small, but relevant statistic is a long story. The personal decisions that Canadians have made about eating beef are intriguing, given the amount of negative media coverage that mad cow disease gets and the uncertainties regarding the science of mad cow.

A risk assessment done by Health Canada for the time period before 1997 rated Canada as a “negligible risk” for mad cow disease. Since then, they have labeled Canada to be a minimal risk for finding the disease among cows. By continuing to consume beef products, it seems that Canadians trust this advice and have not changed their eating habits considerably.

According to Dr. Bill Leiss, however, these studies are completely irrelevant. “A risk assessment is supposed to look ahead, that’s what they have refused to do.”

Leiss is one of the project directors at the McLaughlin Centre for Population Health Risk Assessment at the University of Ottawa. He says, “They don’t have a clue about what’s going to happen after 1997.” He adds that Health Canada has never asked him for help in calculating this risk.

But Dr. Andre Turcotte, a specialist in public policy analysis, says this isn’t a valid argument. “Unless the spread of the disease is proven to occur quicker than it used to, whatever was going on prior to 1997 is applicable to today.”

Summing up the status of mad cow disease in Canada in one word takes a lot of math and science. The word minimal did not just materialize at the whim of Canadian politicians and cattle ranchers. Many different factors must be taken into account before the Canadian government can advise the public about the risks of eating beef.

First, the hazard itself must be identified. Right now, the theories surrounding BSE are far from being complete. Transmissible spongiform encephalopathies (TSEs), like mad cow disease, kuru in humans, scrapie in sheep and chronic wasting disease in elk and deer, are all rooted in the theory of prions (pronounced PREE-ahns).

Prions are microscopic-sized specks of protein floating around the body. Brains, for example, are made up of millions of specks of protein. Scientists don’t know quite how, but bad prions (called PrPSc) cause changes in good prions (PrPC). They seem to act like a virus because they multiply, but they don’t have any genetic information, which eliminates them from the virus category.

Think of prions as the kid at school who is a bad influence on the other kids. Prions attach themselves onto functional pieces of protein and change their structure. The changed proteins have now been converted and can influence more good protein bits into developing bad qualities as well. In this way, the disease multiplies and eventually forms holes in the brain, inevitably shutting down an entire nervous system.

The disease that is thought to be transferred from cows to humans through prions is called variant Creutzfeldt-Jakob disease. It brings a lot of nasty psychiatric effects, like frightening hallucinations, vivid delusions of reality, extreme forgetfulness, and eventually death. The patient is also aware of his or her mental deterioration as death approaches.

The second phase of a risk assessment looks at exposure. Potentially, bad prions from cows can be transmitted through many different routes. Most scientists believe that staying away from eating food made of brain or spinal cord material will stave off the illness. In other words, any sausages and “mystery meat” products should be considered a hazard.

Scientists also have not come to a conclusion on this part of the theory. They don’t know how, or if, the disease jumps from species to species. Dr. Aru Balachandran from the Canadian Food Inspection Agency is an expert on TSEs. “There is a theory that prions could jump, but I trust science to a greater extent than I do magic.”

He says there are subtle differences at the molecular level, between the prions that devastate different species. Cows are affected by a certain prion, and the prion that kills humans is another type of prion, which is structured in a different way. If the theory of prion transfer between species turns out to be true, one thing is for sure, he says, “It’s very difficult to break the species barrier, but [transmission is] less difficult within species.”

Another way of interpreting the jumping theory is that the prions must express a change in structure to facilitate a jump between species. In many scientific circles, this can also be seen as the reason for the molecular differences between species.

Genetic makeup determines human disease

There are still more mysteries about whether genetics determines susceptibility to a bad prion’s nasty effects. This is also something Dr. Balachandran believes in. “Genetics plays a role in determining who contracts the disease,” he says.

Leiss agrees. “Of the 140-145 people who’ve died so far, almost all of them had a kind of signature genetic makeup that made them susceptible to getting sick,” he says. “So that’s sort of comforting to the rest of us.” Meanwhile, a few other scientists believe bad prions can affect anyone who comes into contact with infected cow brain or spinal cord material.

The third part of an assessment is identifying “the dose,” or how much of a substance must be consumed before a person gets sick. Leiss says this is the most difficult part of studying risk. “If I know how much you have, I can tell you what the probability is that you might get sick. That’s where the numbers come in.”

And there are more than enough numbers. One of the concepts Health Canada has used to try to determine the risk of mad cow disease is probability. Dr. Turcotte says probability is the process of “trying to isolate the chances that something will happen. We are familiar with probability every day. When you play the lottery, there is one chance in a million you will win … The more tickets are sold, the less likely you are to win. The more cows that are sold, the less likely it will end up on your plate.”

Health Canada also looked at the lifespan of a cow in Canada. They determined that the average cow’s life expectancy is seven years. “And then they looked at what they know about the spread of the disease,” Dr. Turcotte says. “There is a high probability that the cow will die before contracting mad cow disease.”

But scientists don’t seem to be in agreement with this point, as many say it is likely that the cow could be incubating the disease without showing any symptoms. Dr. Turcotte says that “it looks like contracting the disease takes longer than the lifespan of a cow. At the end of the day, the likelihood that the steak on your plate is infected is really remote.”

Lab technician, Steve Foster does not worry when he handles potentially infected brains.

So the risk of mad cow disease to the average person looks small, for now. When the most recent Health Canada study becomes public, it may show a clearer picture of this risk. Meanwhile, Steve Foster, a technician in Dr. Balachandran’s lab, says that working with potentially infectious material doesn’t worry him at all.

“Sometimes I go down to the cemetery near my house and I look at the tombstones there. A long time ago, children died very young. We live in good times compared to the early 1900s,” he says. “When so many people die of cardiovascular diseases each year, I don’t think we have to worry about the one in a million stuff … I have to watch my cholesterol, so I figure that’s what’s going to eventually nail me.”