One of the most worrying consequences of Britain's outbreak of "mad cow disease"--that humans might have been infected by consuming contaminated beef--appears to be confirmed by research to be published this week in Nature.
More than 20 Britons have died over recent months of so-called variant Creutzfeldt-Jakob disease (vCJD). The symptoms are similar to those of classic CJD, a fatal brain disease that progresses slowly. But vCJD tends to strike younger people, and it develops much more quickly. A link between vCJD and mad cow disease, bovine spongiform encephalopathy (BSE), has been suspected, because both involve dementia, tremors, and what may be an infectious protein called a prion. But the evidence (ScienceNOW, 23 October 1996) that eating BSE-contaminated beef might cause vCJD has been inconclusive.
In the new work, Moira Bruce of the Institute of Animal Health in Edinburgh, Scotland, and colleagues injected mice with infectious brain samples from cows with BSE, patients who died of vCJD, and classic CJD patients. After examining how and where the mouse brains were damaged, along with the symptoms and course of the disease, the researchers concluded that vCJD and BSE in mice are the same, and both are distinct from classic CJD.
A team from Imperial College School of Medicine in London, led by John Collinge, adds another piece of evidence to the puzzle in a separate Nature paper. Collinge and his colleagues demonstrate biochemically that the infectious agent responsible for BSE can turn normal human prions infectious in mice. The "inescapable conclusion," says Collinge, is that new vCJD is the human equivalent of BSE and that eating infected beef is probably to blame.
A key question now is how many people may have been infected, but researchers still have no answers. "It may take several years before we can be confident that this is not a period of comparative calm before the storm," comments Jeffrey Almond at the University of Reading and John Pattison at University College London. "Much depends on the average incubation time of vCJD, and, at present, we cannot calculate it."