A couple hundred new cases of cattle afflicted with mad cow disease have sent ripples of panic across France and Germany, reviving the specter of the hundreds of thousands of cattle felled since 1986 in Britain by the degenerative brain sickness. People can contract the disease by eating infected meat, but so far human fatalities have been rare. Surprisingly, the disease seems to be transmitted not by microbes but by molecules. Biochemist Byron Caughey of the National Institute of Allergy and Infectious Diseases was one of the first to show how rogue proteins called prions could propagate and potentially lead to mad cow and its human equivalent, Creutzfeldt-Jakob disease (CJD). He discussed the latest health scare with Discover associate editor Josie Glausiusz.
What do you think of the furor underway in Europe over mad cow disease?
It is a nasty disease and I do worry about it, so reasonable measures should be taken to reduce the risk to people. On the other hand, mad cow disease remains low on the list of causes of death in humans, even in Britain. I must say that it is amazing to me the extent to which some people will agonize over the possibility of mad-cow infected meat, which has caused about 90 total cases of CJD over the last four years, yet they will happily smoke the tobacco that apparently results about one death per minute in the European Union.
Do you think we are likely to face a similar crisis in the United States?
No. The most important factor in my mind is a 1997 rule that forbids feeding cattle- or sheep-derived products back to those animals, a practice that originally helped spread mad cow disease in the United Kingdom. (Although a report released by the Food and Drug Administration this January suggests that the U.S. ban is not always enforced.) A similar ban in 1988 in the United Kingdom has dramatically reduced the incidence of mad cow disease there.
Is it safe to eat beef from American cattle?
I think it is nearly as safe as it has ever been. There still has been no direct documentation of a home-grown, naturally occurring case of mad cow disease in U.S. cattle.
Do you eat beef?
Sure. Well, if I went to Europe or Britain I would try to stick to red meat and not the mushed up prepared meats like bologna, sausages, meat pies and lower grades of hamburger, which are likely to contain central nervous system tissue or other much more highly infectious tissues like lymph node and spleen.
What is the potential human death toll from eating infected beef?
That is hard to say. I am not an epidemiologist. However, the rate of appearance of new cases is on the rise. I've heard estimates of anything from hundreds to hundreds of thousands of cases of CJD over the next several decades. Given the much higher exposure of people to infected beef cattle in the UK than elsewhere, I would expect that the incidence would remain much highest there.
How do these diseases arise?
The current hypothesis is that they result from the abnormal folding of prion protein, a protein that is present normally in many tissues in mammals. The misfolded version can cause other, "normal" prion proteins to fold incorrectly as well. The corrupted prion protein then accumulates in the brain to the point where it causes neurodegenerative disease. Alzheimer's and Huntington's diseases seem to involve analogous protein-folding errors. The 'chicken or the egg' question of where the rogue prion protein comes from in the first place is difficult to pin down.
How might we treat or prevent prion diseases?
A few reasonable points of attack would be to prevent infections in the first place, to block migration of the infectious agent from peripheral points of infection to the brain, to block the conversion of normal prion protein to the abnormal, pathogenic form, and, finally, to block the neurotoxic effects of the infection in the brain. We have identified new classes of inhibitors that block the formation of the abnormal prion protein. We now know that they can prolong the lives of infected mice if treatment is begun near the time of infection. But in the case of mad cow disease and CJD, it's difficult to know when that time was.
Does this work make you appreciate the frailty of life?
Well, it certainly is shattering to have family members of CJD patients call on the phone and describe what has happened to their daughter or son or aunt or uncle or wife or husband and the effects it has on the entire family. It's a sober experience, and one that is humbling as well, because you do realize that this can happen to almost anyone.
What inspired you to become a scientist?
Like the Elephant's Child in the Just So Stories, I have always had an insatiable curiosity. It must be curiosity rather than intelligence because who in their right mind would willingly work with these intractable diseases? If they don't kill you, they will drive you crazy.