NEW YORK (Reuters) -- The first direct evidence that humans can contract 'mad cow' disease from animals lies in a protein's biological signature, according to a new study.
The cattle disease, bovine spongiform encephalopathy (BSE), has long been suspected to be caused by the same agent as the degenerative brain disorder Creutzfeldt-Jakob disease (CJD), a disease found in humans. A new variant of CJD, of uncertain origin, has appeared in patients in Europe over the past year.
"That the glycoform [biochemical] 'signature' of new variant CJD is seen in BSE itself... is consistent with the hypothesis that new variant CJD results from BSE transmission [from animals] to humans," concludes a study from researchers at the Imperial College School of Medicine at St Mary's in London.
Creutzfeld-Jakob disease is a brain malady which begins as memory loss and physical incoordination, progressing to a vegetative state.
Researchers explain that both CJD and BSE are believed to be caused by infectious particles called prions. The London researchers compared the particular biochemical properties of prions in tissue samples taken from monkeys and mice infected with BSE to samples from the human victims of new-variant CJD.
"The biochemical signature of prions in patients who died from the new variant [CJD] matches that of prions in mice and macaque monkeys experimentally infected with BSE," says a statement from the journal Nature, which published the study.
It notes that this 'marker' does not match that of the previous variant of CJD, a disease which has so far struck only a few Britons. With such a small human population infected, researchers feel it's not feasible that a mutant strain of CJD occurred within humans alone, saying "the spontaneous occurrence of an identical new type [of CJD] in 12 individuals in the U.K. over the past two years [is] extraordinarily unlikely." Then, just what is the origin of new-variant CJD? According to the researchers, "This [new-variant CJD] is probably a new animal strain."
The findings are "further evidence that the BSE agent has been transmitted to man," writes Adriano Aguzzi from the Institute of Pathology at the University of Zurich in a Nature editorial.
The researchers say the biochemical marker may make diagnosis easier in a disease which, so far, has only found diagnosis via postmortem brain biopsy. Noting that prion proteins can be found in other areas of the body besides the brain, "it may be possible to detect this molecular marker of new variant CJD in tonsil or lymph-node biopsy and thereby avoid brain biopsy," they conclude.
This study follows on the heels of study released by German researchers who demonstrated 84% accuracy in spotting the same protein of new-variant CJD in spinal tap sampling of cerebral spinal fluid.
SOURCE: Nature (1996;383:685-688)
