Link Between Mad Cow Disease and Human Deaths Questioned
Oct. 11, 2001 -- Mad cow disease strikes fear into the hearts of meat lovers everywhere, and with good reason. Although slightly more than 100 deaths have been attributed to eating contaminated beef, some researchers speculate that millions of people may one day fall victim to the fatal human form of the disease as a result of eating a single tainted burger or steak.
But provocative new research questions the link between infection in cattle and that in humans. Writing in the Oct. 13 issue of the British Medical Journal, Scottish epidemiologist George Venters, MD, of NHS Lanarkshire, argues that there is no clear evidence to prove that mad cow disease can be transmitted to humans by ingesting contaminated meat products. He adds that the case for such transmission is weak.
"This will undoubtedly be controversial within the scientific community, but that is part of the point," Venters tells WebMD. "I want to prompt more appropriate explanations about what is going on here than the facile one of infection. The infectivity hypothesis is, in fact, becoming a bit threadbare."
Mad cow disease, known medically as bovine spongiform encephalopathy (BSE), was first identified among British cattle in 1986 and has since spread throughout Europe. Since the mid 1990s, scientists have become increasingly convinced that a recently identified, rapidly degenerative, fatal brain disease in humans called new variant Creutzfeldt-Jakob disease (CJD) is caused by eating the meat of infected cattle.
Venters says there may be nothing new about new variant CJD. He suggests the cases classified as such may actually have been classical CJD, which is not a food-borne illness at all.
"If you have a food-borne infection, you expect the number of cases to rise at the same rate as the population was exposed to the infection," Venters says. "That has not happened here. People try to explain this by saying there may be a long incubation period, but the fact is that you have had cases occurring for seven or eight years now and the numbers have not been increasing."
Venters calls new variant CJD "the epidemic that never was," because its numbers have not increased dramatically in the years since it was identified. Using established research methods, Venters says he could find no direct evidence that the infectious proteins known as prions, which cause BSE in cattle, are infectious to humans.
"It is unlikely that human beings who eat prions from other species are likely to get infected, because our own defenses are well enough organized to digest or to destroy these prions," he says.
But prion researcher Robert B. Petersen, PhD, disagrees and says while some of Venters' assumptions may seem valid on paper, they just don't reflect what is going on. Petersen says studies have shown that the molecular signatures of BSE and new variant CJD are virtually identical. And animal studies have confirmed the pathological similarities of the two diseases. Petersen is an associate professor of pathology at Cleveland's Case Western Reserve University and is chief scientific officer for a company working to develop a diagnostic test for BSE.