A team of scientists working on the link between Bovine Spongiform Encephalopathy (BSE or "Mad Cow Disease") and the degenerative brain condition found in humans, (new) variant Creutzfeldt-Jakob disease (nvCJD or vCJD), have made a significant breakthrough. The research, which has been carried out by doctors in Scotland and the US, found that the infectious agents, or prions, that cause both BSE and vCJD produced exactly the same disease characteristics when injected into laboratory mice.

One of the researchers behind the study, Professor Stephen DeArmond from the University of California, San Francisco, said, "taken together with other evidence, the link is now indisputable".

The scientists, led by Michael Scott from the University of California and Robert Will at the British government's CJD Surveillance Unit in Edinburgh, found that when diseased human brain tissue was injected into mice, the results were identical to those produced by the injection of BSE-infected bovine material. In both instances there was no apparent sign of a "species barrier" preventing the disease passing from cattle to humans. The incubation period was the same—250 days—and the pattern of brain damage was identical.

The results, reported in the Proceedings of the National Academy of Sciences, suggest that BSE and vCJD are interchangeable. The scientists injected transgenic mice, whose own genetic makeup had been altered, with infectious material from cattle and humans. "That human nvCJD prions so precisely duplicate the properties of native bovine BSE prions in their behaviour on transmission into ... transgenic mice creates a compelling argument for an etiological [causal] link between BSE and nvCJD.