The hard truths about mad cow: Top expert reveals much is yet unknown about the disease
February 12, 2006
The Calgary Herald
Gina Teel
When it comes to mad cow disease, or BSE as scientists prefer to call it, Dr. Jean-Philippe Deslys is the go-to guy.
One of the world's leading authorities on BSE and top researchers in the area of prions, the misfolded proteins linked to BSE, the Paris-based Deslys is part of an International Research Advisory Council. The council will provide strategic direction to the newly minted $35-million Alberta Prion Research Institute.
Head of the Prion Group at the French Atomic Energy Commission, Deslys is also project coordinator for the European Network of Excellence or NeuroPrion, and is an advisor to the World Health Organization and the U.S. Food and Drug Administration.
In addition to his research, which includes, among other things, the human susceptibility to prion contamination, Deslys is author of Mad Cow Disease: The Risk to Humans.
Deslys also helped in the development of a rapid diagnostic test for BSE, known as the Bio-Rad test. He advocates the mandatory testing of all cattle over 30 months of age.
Q: In Alberta we've had another case of BSE diagnosed recently in an animal born after the feed ban. I know the science says, based on what's happened in Scotland and elsewhere, that this is not unusual.
What are your thoughts on this latest case -- is it a surprise we're finding it?
A: It is not a surprise. We have seen it in all the countries. The measures taken to protect the food of the animals are not absolute. We know that there are holes in the system and that it can happen. Even recently in the U.K., a very young animal last year developed the disease, so that's an abnormality suggesting an important infectious dose that could have entered into his foodstuff.
In Poland last year they also had a young case, so it indicates that despite the very strict measures which have been taken, you have holes in the system.
We are dealing with thousands of tonnes of materials, so as these are global measures, of course by definition, you can have the possibility of escape.
Q: In this particular instance, in our last case, the CFIA said in its initial investigation that there's no indication the farmer did anything wrong. It may have been something as simple as a piece of feed that he no longer used being stuck in the corner of a bin.
A: It's also the explanation which has been given for the U.K., so you can imagine everything. By definition when you have only one animal which is involved and this is five or six years after the contamination, it's almost impossible to know exactly what happened.
A: Is there any concern at this point of some of these incidences being related to a sporadic form of BSE?
Q: That's true that we have now this problem of the possibility of a sporadic form of the disease. We have these atypical cases of BSE which have been described in Italy, France and Germany, which occur in older animals and for some people it could be indicative perhaps of the origin of BSE, which would come from these kinds of cases. Perhaps it's something else, we don't know.
Q: When you say older, how much older?
A: They are between nine and 11 years, so these are old animals.
Q: To the question of testing, you advocate mandatory testing of all animals over 30 months of age, correct?
A: I think that it's the best solution to protect at the same time the consumer and the profession, meaning the beef industry.
Because even if you have still very limited cases, if you can give the guarantee that they cannot enter into the food chain because they are detected, then you increase the confidence and you have no more problem of exportation neither, because some countries don't want to see animals which have not been tested over 30 months, so everybody can be happy with that.
Q: Currently, again, its the four Ds (high risk) we target here.
A: It's very logical this politic from an epidemiological point of view. If you don't want to test everything, you limit the test to the higher risk categories. That is exactly what is done.
Q: In the U.K., BSE has something like 180 human deaths related to it. Can you put that into perspective for me in terms of human health?
A: You have to make a clear difference between the risk assessment and the perception of the risk.
I remember that I've made a talk in front of medical doctors explaining the risk, and the conclusions were that in the meat, the muscle, if there was a removal of specific risk materials and that they (animals) were tested, there were absolutely no risk.
The conclusion of one of them after that was, OK, I stop eating meat, and she was smoking. So I told her, explain to me why you have this reaction, why you are taking a cigarette which has an incredibly higher probability to kill you?
Her reply was fantastic. She said, 'Yes I know. Rationally, I know. But I don't feel it like this.'
You have to understand that you are dealing with diseases which destroy your brain, there is no treatment, these agents, you don't know when you are infected, those who are involved are young, so potentially it is your children who are involved, so you have a lot of psychological conditions which bring you to the conclusion that OK, I prefer not to take the risk, even if it's not rational.
Q: Tell me about the study you were doing about the oral transmission of BSE.
A: It was transmission by oral route in primate. The idea was how can we estimate the minimal dangerous dose for man. And in fact what we have determined was an estimation of what we call the LD50 . . . the dose which has a probability of 50 per cent to kill you.
Only one of the animals developed the disease indicating the five grams of (highly infectious) brain we gave to him we had enough infectivity to have this probability of killing him.
Here was the calculation, saying if we take these brains we have used to infect this animal and then dilute it 300 times, we still have a positive signal with the test, meaning that the animal would have been blocked at the slaughterhouse.
Then, imagine the infectivity was under this dilution, it implies that to obtain the equivalent of what was in your five grams, you would have to eat 300 times more, because it was diluted, so more than 1.5 kilograms. You can't find it even in a single animal. It's double the weight of the brain and spinal cord.
That was a demonstration why a sensitive test combined with the removal of specified risk material was very efficient.
Q: How much do we know about BSE versus how much we don't know?
A: For the consumer and our population, the scientific knowledge accumulated has allowed to define wide safety areas: in Europe the safety of beef products is notably obtained by the exclusion of specific offals as brain and spinal cord combined with the systematic testing of slaughtered cattle over 30 months.
Concerning science, major uncertainties remain, including the precise nature of the infectious agent responsible for BSE, and very strong research efforts are still needed.
Q: Humans have a threshold for this like they would anything else, but the amount of infectivity isn't available?
A: Yes. When you test with a sensitive test and that you have the removal of the specified material.
Compare the situation with estimates that two million of infected cattle entered into the human food chain in the U.K. They have only 157 human cases for the moment. They will have more, of course. Unfortunately the disease is a very long incubation disease. But despite of this, you understand it is not so easy to transmit it to humans, even when you don't take the proper measures.
Q: Where are you at with the disease and how much more work needs to be done?
A: In Europe, BSE is behind us. Concerning cattle, the measures have been very efficient. Concerning small ruminants, we had an alarm last year with a BSE diagnosis in a goat, but finally also with the testing programs people have been reassured that as it was something linked also to contamination between the total ban on meat and bone meal. And no other cases despite extensive testing have been found, and it was an animal born before the total ban.
We are deeply involved in the decontamination studies. Because as these agents are very resistant, how can we guarantee that the instruments that even the factories, it's true for the pharmaceutical industry but for the slaughterhouse also, how are we sure they are cleaned properly in case of a case diagnosed or even not diagnosed, so there is no cross-contamination.
And now the things are moving to (human blood) transfusion. So that's becoming our main concern.
Q: Right, I wanted to talk to you about that. Why is that?
A: Because two people developed vCJD in the U.K. linked to transfusion after having had several years earlier a blood donation from a donor who developed later vCJD. He was during the silent incubation phase of the disease. It symbolized a very high rate of transmission because it's two positive transmissions out of 18 patients who received the blood and who survived through the blood donation, because of course transfusion is done always in case of important disease or surgery.
So people are really very concerned about it. The problem is how can we guarantee the safety of the transfusion, knowing that we cannot stop having blood. So a big effort is put now on the development, not only on risk assessment, of course, on new and things which are being developed . . . for example filters to trap the infectivity and protect the blood transfusions, so that's a possibility. Other things are blood testing, which are developing.
The problem is that we are going to enter into a intermediary phase where we are going to be able to demonstrate that there is infectivity in blood, but not to guarantee that what is seen as negative is safe, so it will be difficult to manage.
Q: What are your thoughts on this agent, where it comes from and what it's capable of?
A: The agent, and all the prion diseases, each time you let them multiply you have a risk of having a big trouble.
From one infectious particle that you can transmit to one animal, when the animal develops the disease there are billions of infectious particles in its brain and its spinal cord, notably. So if you enable it to be retransmitted to other animals, you have a terrible circle.
The problem is BSE. You have the chronic wasting disease which at the beginning was very limited and which now is expanding, and that we do not know how to control. So this agent is going to be in closer contact with more and more people, not only hunters but also other people, and that's not a good thing.
Q: Is there a risk with CWD? I saw an article the other day saying there was a concern for hunters handling meat from animals, not knowing whether they were infected or not.
A: The higher risk is with the herds themselves and with tissues in contact with brain and spinal cord. However, you have risk also with lymphoid tissues. So you are then almost everywhere, lymphnodes are even within some muscles.
So far there at the moment there is absolutely no demonstration that CWD is dangerous for man. However, as it's highly infectious between animals and as it is spreading more and more, it is not recommended to favour the contact with humans.
Q: So the work here at the institute is going to focus on obviously trying to solve the BSE mystery but also trying to get a handle on CWD transmission?
A: They are going to go much further than this because the idea is also to use the interest in this agent to try and understand more, notably the Alzheimer's disease, and all the diseases where there are misfolded proteins, and that's a real challenge.
