Scientist: 'Mad Cow' May Not Cause Human Illness

From Reuters - October 12, 2001

Mad cow disease and the illness thought to be its human equivalent may not be linked after all.

George Venters, an expert in public health medicine in Hamilton, Scotland, believes the rogue prion brain protein that causes mad cow disease, or bovine spongiform encephalopathy (BSE), does not cause new variant Creutzfeldt-Jakob Disease (vCJD) -- a degenerative brain disease found in humans.

Venters said he does not believe that the evidence now available casts serious doubts on the case for a causal link between bovine spongiform encephalopathy and new variant Creutzfeldt-Jakob disease and that the epidemiological evidence just doesn't stack up.
The link between the animal and human brain-wasting diseases is open to question, he added, because it does not meet criteria used by scientists to assess a link between cause and effect for disease.

When you apply them to the case of BSE causing vCJD, the evidence is weak. A telling point is the number and pattern of cases detected is different from what you usually find in epidemics caused by eating contaminated food.

British scientists first identified vCJD in 1996 and suggested eating meat infected with BSE was the cause. The condition causes degeneration of the victim's brain tissue and eventual death.

But Venters said there is no direct evidence that the prion responsible for BSE and other animal diseases is infectious in humans.

Prions in animals and humans are different, he argues, and humans do not get other animal prion diseases such as scrapie -- found in sheep -- from eating lamb.

Also, ingestion is an inefficient route of transmission of prions other than by cannibalism. Infection of humans from eating the bovine spongiform encephalopathy prion is therefore unlikely.

In a report in the British Medical Journal, Venters listed other inconsistencies including the relatively small number of cases of vCJD, lack of details about exposure to the infectious agent and the pattern of infection, which does not fit in with other food-borne diseases.
If vCJD is caused by eating beef contaminated with BSE, Venters said the number of cases should be much higher than the 100 or so confirmed cases reported so far.