Two studies show that the strain of prion disease that causes the new variant of brain-wasting Creutzfeldt-Jacob disease vCJD) is identical to bovine spongiform encephalopathy (BSE) in cattle.

In experiments that ran for more than a year, Moira Bruce of the Institute of Animal Health in Edinburgh, Scotland, and her colleagues injected several different breeds of laboratory mouse with infectious brain samples from cows, patients with vCJD, patients with sporadic CJD and farmers who died of CJD after working with animals with BSE.
The injection of infectious material served to bypass any protection the animal's gut may have afforded.

The researchers looked critically at the incubation time (the time it took for the injected mice to fall ill), the type of brain damage caused, and the areas of brain damaged. The research shows that the histological presentation, symptoms and course of vCJD in mice is identical to that of BSE in mice, and distinct from other forms of CJD. The strain of CJD that killed the farmers by CJD was not the same as BSE, confirming earlier results this year published elsewhere (The Lancet 350, 188; 1997).

In a second series of experiments, John Collinge of the Prion Disease Group, Imperial College School of Medicine at St Mary's, London, UK, and his colleagues describe a completely different approach that led to the same conclusion -- that vCJD is caused by the same agent as BSE.
Using a biochemical assay, Collinge and colleagues show that the BSE and vCJD agents are the same, and are distinct from other forms of CJD in humans.

Collinge and colleagues show that the disease agent that causes BSE is able to 'convert' human prion protein into the highly resilient, pathogenic form of the protein, when tested in mice.
Genetically engineered or 'transgenic' mice which have had their native mouse prion protein gene replaced with a human prion protein gene do, eventually, contract spongiform encephalopathy after injection with BSE contaminated material. Collinge and colleagues reported in Nature in 1995 (Nature 378, 779-783) that these mice do not become ill even 200 days after inoculation. The researchers waited longer, and now report that mice succumb after 500 days.