A mysterious case of Creutzfeldt-Jakob disease (CJD) has raised fears more people than thought could be at risk.
New Scientist magazine reports the genetic make-up of a 40-year-old woman who may have died from variant CJD was different to all other patients so far.
But the University College London study's lead researcher said it was too early to say for sure.
And a government advisor on CJD said many cases needed to emerge to confirm a new wave and people should not panic.
CJD is a fatal brain condition, with dozens of cases every year.
However, the BSE crisis in cattle in the 1980s and 1990s saw the emergence of a new form of the disease.
A small number of people who ate infected material from cattle at that time went on to develop variant CJD, a similar and equally lethal illness, which often did not emerge until years after the infected meat was eaten.
After a slaughtering programme removed infected cattle from the food chain, deaths from variant CJD were thought to have peaked in the first half of this decade, falling steadily since 2003.
However, the latest find opens a small possibility that the "incubation period" for some people may be longer, and that there could be a second upsurge in deaths to come.
Every person who has died from variant CJD before this point has one thing in common - they carry a gene variant called MM.
About four in 10 people has this variant, and some experts believed it was possible that in humans, only these people may ever have been vulnerable to variant CJD.
The latest death is the first recorded involving a different variant - VV - found in approximately one in 10 Britons.
Lead researcher Dr Simon Mead, from the Prion Unit at University College London, whose work was originally published in the journal Archives of Neurology, said that at the moment it was too early to say whether this signalled the beginning of a rise in cases among other VV carriers exposed to BSE-infected meat.
He said: "We can't say for sure whether this is actually variant CJD, or simply a case of "sporadic" CJD in a younger-than-expected patient - it does not have all the features of either.
"It could be a new type of variant CJD affecting VV people, but we would need to see a lot more cases than at present to confirm this.
"What we are doing at the moment is asking people to stay alert and look out for other cases."
Professor Chris Higgins, the Chair of the government's Spongiform Encephalopathy Advisory Committee (SEAC), which advises on variant CJD, played down fears that cases could rise again.
He said: "There's certainly no need to panic. This could simply be a case of sporadic CJD, in which case the genetic makeup is irrelevant, as this is found in MM and VV people.
"At the moment there isn't enough evidence to conclude one way or the other.
"We know that it is possible to infect VV mice with variant CJD, but it is actually much harder than infecting MM mice, so even if there were to be a rise, it would not a big rise."
To date there have been 114 deaths from variant CJD in the UK, with another 47 deaths thought likely to be due to the disease. ( BBC )