FEARS of a new wave of deaths caused by the human form of mad cow disease have been triggered by a type of variant CJD never seen before.
Scientists who examined the brain of a 39-year-old woman killed by the disease found unusual patterns of damage.
The woman also had a distinct genetic make-up associated with her illness that was not shared by other victims.
Investigations are still at an early stage, but the findings point to the possibility of a further group of people succumbing to vCJD as a result of having eaten infected beef in the 1980s.
The disease, linked to misshapen prion proteins in the brain, has varying incubation periods according to genetic make-up.
Experts believe that for many of those infected the timer could still be ticking, and in some cases the incubation period might exceed 50 years.
VCJD originally arose in cattle as bovine spongiform encephalopathy (BSE), or "mad cow disease", before appearing in a new form in humans.
The incurable disease leaves the brain riddled with holes, like a sponge, causing a loss of mental faculties and eventually death.
Since the disease was first recognised in 1995 there have been 162 confirmed or suspected vCJD deaths in the UK.
Fears of an epidemic involving hundreds of thousands of deaths abated after the number of annual deaths peaked at 28 in 2000 and then quickly fell.
In the year up to 30 November, 2007 there were just four definite or probable cases.
All these people had the MM version of the gene that makes prions, carried by 40 per cent of the population. The woman had a different gene variant.
The case was described in the journal Archives of Neurology and reported yesterday in New Scientist magazine.