Mad cow disease diagnosed in humans - evidence found that cows can transmit bovine spongiform encephalopathy to people - Biomedicine - Brief Article

Science News, Nov 2, 1996

News that mad cow disease might have cropped up in 12 people this spring--perhaps as a result of eating meat from infected British cattle (SN: 4/13/96, p. 228)--sent researchers scrambling to their labs. There they focused on PrP, a protein suspected of causing that disease and some other fatal brain disorders in humans, including Creutzfeldt-Jakob disease (CJD).

Now, British researchers report they have direct evidence that mad cow disease, or bovine spongiform encephalopathy, was indeed transmitted from cattle to people. The evidence lies in PrP's shape, which appears to determine whether it coexists harmlessly with other proteins in brain cells or wreaks havoc.

Earlier studies indicated that normal PrP and its warped, disease-causing alter ego, known as a prion, are biochemically identical. This finding led researchers to conclude that changes in PrP structure result in functional differences, which would account for the different symptoms among infected species. They also theorized that a prion, which has no genetic material, replicates by twisting normal PrP into its own image.

John Collinge of the Prion Disease Group in the Imperial College School of Medicine at St. Mary's in London and his colleagues report in the Oct. 24 NATURE that they can exploit the different shapes to trace the transmission of prion strains within and between species.

The team used a standard laboratory technique to generate a band pattern for each protein. They found that most prions taken from different hosts formed distinctly different patterns. Since the proteins are biochemically alike, the variations probably signal differences in their shape.

The band pattern of prions taken from people who died of the human variant of mad cow disease matched the pattern from mice and monkeys infected in the lab with mad cow disease. It differed from the band pattern of prions from people with CJD. Such differences could form the basis of a new diagnostic test (SN: 10/12/96, p. 238), the researchers say.

Adriano Aguzzi and Charles Weissmann of Zurich University say in an accompanying editorial that the new work represents "an exciting new approach" to the study of prions and the role they play in these rare brain diseases.