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Mad cow disease can be spread by airborne particles, researchers warn.
And they fear that those who work in abattoirs, slaughterhouses and laboratories could be at risk.
Their study shows prions, the infectious agents which cause BSE and its human form, variant Creutzfeldt-Jakob Disease, can be dangerous if carried through the air.
In tests, mice who breathed them in developed the brain disease with 'frightening' speed and died.
The discovery could also explain why some of the victims in the 1990s were vegetarians.
Since the link between BSE-infected meat and vCJD was confirmed in 1996, 170 have died. Deaths peaked in 2000 when 28 died. Last year, there were three victims.
Prions, a type of protein, can spread on surgical instruments and in blood transfusions. It had been assumed they were not transmitted by air.
But Swiss researcher Dr Adriano Aguzzi at University Hospital Zurich and colleagues exposed laboratory mice to aerosols containing prions in a specially designed chamber.