Links to mad cow disease unclear
March 26, 2006
The Birmingham News
Jean Weese
On the issue of so-called mad cow disease, I remain a steadfast cynic - one of a small, but growing number of scientists around the world who doubt that people contract a brain-wasting disease, known as variant Creutzfeldt-Jakob disease, from a similar disease in cattle known as BSE, commonly called mad cow disease.
I should stress that the recent discovery of BSE in an aging Alabama cow hasn't changed my views at all. If anything, what investigators ultimately learn about this cow may reinforce my longstanding suspicion that BSE is the 21st-century version of pellagra, a disease that once was as widely feared as it was misunderstood.
Proponents of a link between BSE and variant CJD in humans have always pointed to a smoking gun - the modest increase in variant CJD cases in the United Kingdom that corresponded with a huge spike in BSE outbreaks in British cattle in the 1990s.
The culprit, they believe, is an aberrant protein, commonly called a prion, which presumably is ingested by cattle from contaminated feed and passed on to humans who consume beef from these infected animals.
Admittedly, the image of one's brain turning into sponge - the inevitable result of variant Creutzfeldt-Jakob disease - after eating tainted beef is a horrifying one. But is it grounded in scientific fact?
A number of experts around the world have raised this question and come up empty-handed.
For starters, the prions associated with cows and humans aren't the same - a fact underscored by Dr. George Venters, a British health consultant, writing in what turned out to be a hotly debated article in the British Medical Journal in October, 2001. As Venters maintained, the prions associated with ungulates, or hooved animals, have different sequences of amino acids than those associated with humans. That raises another question: How did such a radically different prion manage to surmount the "robust species barrier" between cows and humans?
Venter's observations have been borne out in research: Laboratory mice genetically altered to carry the human prion associated with variant CJD have not developed BSE even after being injected with the cattle prion.
For that matter, how do we know the modest rise in the CJD cases that corresponded with the huge spike in BSE cases in British cattle in the 1990s wasn't merely a fluke - one of those bizarre statistical anomalies, sort of like when lightning strikes twice in the same place? For a time, British health authorities even feared the huge spike in BSE cases would be accompanied by a similar surge in human cases. It never happened.
A number of other experts have weighed into this contentious scientific debate to question the presumed link between BSE and CJD.
Danny Matthews, an international renowned BSE expert in Wexbridge, England, even speculates that some cases of BSE occur spontaneously in cattle, much as a certain type of Creutzfeldt-Jakob disease, known as classic CJD, occurs in humans, typically as they age. This view could have major implications for BSE-related research worldwide, challenging the conventional view that all cases of BSE in cattle are caused by tainted feed.
Matthews' views are shared by Bob Church, a Canadian beef expert, who believes the first and second cases of BSE detected in Canada occurred spontaneously and were not the result of tainted feed.
This brings us back to the Alabama cow. An investigation of the animal by a local veterinarian revealed the animal likely was an older cow, roughly 10 years old. Could it be that this aging animal succumbed to a bovine form of classic CJD? This is by no means certain, of course, but it would mean the animal's death was not caused from eating tainted feed.
History provides some fascinating examples of scientific investigators debunking widely held views about common diseases. Less than a century ago, most scientists stubbornly held to the view that pellagra was spread from person to person, until an investigator in a surgeon general's study provided conclusive proof it was caused by dietary deficiencies.
Granted, lots of questions remain about BSE, but one should remember that even the most sacrosanct views are vulnerable to closer investigation. In the end, BSE may turn out to be one of them. Jean Weese is an Alabama Cooperative Extension System food scientist and Auburn University professor of nutrition and food science. E-mail: weesesj@auburn.edu.
