More deaths from mad cow disease predicted
"A human BSE epidemic may be multiphasic, and recent estimates of the size of the vCJD epidemic based on uniform genetic susceptibility could be substantial underestimations"
Researchers think variant CJD can now stay dormant for more than 50 years.
So far around 160 cases have been reported in the UK.
Professor Hugh Pennington's an expert on the subject at Aberdeen University.
Other cases have also been reported in France, Italy, Ireland, the Netherlands, Canada, Japan, and the US.
Writing in The Lancet medical journal, scientists based their findings on examining another human prion (microscopic infectious agent) disease called kuru.
Professor John Collinge, of University College, London, led a team th#at studied kuru, the only example of a major human prion disease epidemic available.
Kuru is caused by cannibalism and reached epidemic proportions in some Papua New Guinea communities.
There, eating dead relatives as a mark of respect and mourning was ritual practice until it was banned in the 1950s.
In the study, 11 patients with kuru were identified between July 1996 to June 2004.
As the latest year of birth recorded for a patient with kuru was 1959, the authors assumed that catching the disease through cannibalism would have stopped by 1960.
They worked out that the minimum incubation period - if taken between 1960 and the date of onset of kuru in the patients - ranged from 34 to 41 years. However, in men estimated incubation periods ranged from 39 to 56 years and could have been up to seven years longer.
The authors believe the incubation period for BSE prions in humans could be even longer than that seen in kuru because infection between different species typically takes longer than within the same species.
Professor Collinge said vCJD patients identified so far "could represent a distinct genetic subpopulation with unusually short incubation periods for BSE.
"A human BSE epidemic may be multiphasic, and recent estimates of the size of the vCJD epidemic based on uniform genetic susceptibility could be substantial underestimations," he said.
Human mad cow epidemic 'could be bigger than feared'
Far more people in the UK could be infected with the human form of mad cow disease than originally estimated, scientists warned today.
The scientists believe the time between infection with bovine spongiform encephalopathy (BSE), so-called mad cow disease, and developing vCJD could be more than 50 years. They warned that recent estimates of the size of the vCJD epidemic could be "substantial underestimations".
Exposure to BSE in the UK has been widespread, although just 160 vCJD patients have been identified, leading scientists to investigate why more people have not developed the deadly condition.
It reached epidemic proportions in some Papua New Guinea communities who ate their dead relatives as a mark of respect and mourning until the ritual practice was banned in the 1950s.
In the study, 11 patients with kuru were identified between July 1996 and June 2004. As the latest year of birth recorded for a patient with kuru was 1959, it was assumed that catching the disease through cannibalism would have stopped by 1960.
The scientists worked out that the minimum incubation period of kuru - if taken between 1960 and the date of onset of the disease in patients - ranged from 34 to 41 years. In men, estimated incubation periods ranged from 39 to 56 years and could have been up to seven years longer.
The researchers believe the incubation period for vCJD could be even longer than that for kuru because the infection is transmitted from a different animal - and cross-species infections usually take longer to develop than those within the same species.
The study warned that the full scope of the vCJD epidemic "remains uncertain" and the number of people infected is "still unknown".
"Any belief that vCJD incidence has peaked and that we are now through the worst of this sinister disease must now be treated with extreme scepticism," it said.
Furthermore the researchers, led by Professor John Collinge of University College, London, said some people were more likely to be susceptible to developing the disease. The professor said those vCJD patients already identified "could represent a distinct genetic subpopulation with unusually short incubation periods for BSE."
According to the CJD surveillance unit in Edinburgh, 2,079 suspected cases of all types of CJD have been reported to them since 1990. Of those, 111 were fatal and vCJD was confirmed as the cause of death, while the disease was considered the probable cause of death in a further 45 cases. There are five people in the UK known to be living with vCJD.
Cannibalism Study May Hold Clues for Mad-Cow Disease
The findings suggest the eventual size of a variant Creutzfeldt-Jacob disease epidemic may be much bigger than previously thought, U.K. researchers including John Collinge of the University College London wrote in this week's The Lancet.
Bovine Spongiform Encephalopathy, or mad-cow disease, was first found in the U.K. in 1986. Humans catch the disease through meat from cattle that have eaten feed mixed with ground-up parts of infected animals. About 160 U.K. residents have been diagnosed with the disease, with cases also reported in the U.S. and Japan.
``A human BSE epidemic may be multiphasic,'' Collinge said in The Lancet. ``Recent estimates of the size of the variant Creutzfeldt-Jacob disease epidemic based on uniform genetic susceptibility could be substantial underestimations.''
The disease is caused by abnormal prions, a type of protein that damages the patient's central nervous system. The prions unfold in the brain, creating vast dead spots.
The researchers studied kuru, a disease caused by cannibalism that reached epidemic proportions in some areas of Papa New Guinea. The cannibalism, which was a ritual mourning practice, was stopped by Australian authorities in the 1950s. The researchers identified 11 patients with kuru and found that estimated incubations periods were as long as 56 years and may have been seven years longer.
The incubation period for BSE prions in humans may be even longer because infection between species typically takes longer than within species, the researchers wrote. The patients identified so far may ``represent a distinct genetic subpopulation with unusually short incubations periods for BSE,'' Collinge said.
Dutch health officials have found a second patient with the human form of the mad-cow disease, the National Institute for Public Health and the Environment said yesterday.
``The cause of the disease may be linked to consumption of infected beef in the past,'' it said. ``Currently it is safe to consume beef in the Netherlands, because since 2001 possibly infected cows get tested for the disease when being slaughtered.''
Japan will send three teams on June 24 to inspect 35 U.S. meatpacking plants certified to export beef, as part of an agreement under which it will resume U.S. imports. Japan halted imports of U.S. beef on Jan. 20, just weeks after lifting a two- year embargo, after banned cattle material was found in a shipment of veal.
Before the ban Japan was the biggest buyer of U.S. beef, purchasing $1.4 billion out of a total $3.8 billion in exports in 2003. Japan first halted imports in December 2003 after a case of mad-cow disease was found in Washington state.
During that time, victims with silent infection could pass on the prions via blood transfusions, organ or tissue donations or insufficiently sterilised metal surgical instruments.
In a unique piece of research which continues the meticulous records that have tracked the epidemic of kuru - the "shivering" disease - since 1957, Australian, British and PNG researchers tracked a group of 11 former cannibals dying from the always fatal prion disease between 1996 and 2004.
Forming the tail-end of the epidemic, they were all born before 1950 and took part in endocannibalism, a ritual in which the whole body of deceased relatives was consumed as a sign of love and respect. The ritual was eradicated by Australian authorities by 1960.
The data gathered on these victims and published today in The Lancet have provided a model using actual cases instead of the usual mathematical modelling for future predictions for those infected after eating beef products contaminated with bovine spongiform encephalopathy (BSE). The human equivalent of BSE is variant Creutzfeldt-Jakob disease (vCJD).
Apart from the emerging epidemic of vCJD, in which 192 people have died since 1995 - mainly in Britain, but also in France, Ireland, Canada, the US, Saudi Arabia, Japan, Italy, Hong Kong and the Netherlands - kuru is the only other major human epidemic of prion disease with an oral transmission route.
British prion experts, including Professor John Collinge from University College London, and Professor Michael Alpers from Curtin University - the Australian kuru expert who has followed the disease since arriving in PNG in 1962 - calculated the minimum incubation period for kuru starting at 1960 to the birth year of the last recorded patient.
That minimum incubation time ranged from 34 to 41 years but in men it was calculated to be between 39 and 56 years - and possibly up to seven years longer.
For vCJD it might be even longer, because the infection was transmitted between species, from cows to humans, which usually takes longer than infection within the same species.
Australian prion experts have closely monitored the decade-old vCJD epidemic, and have long recognised from continuing kuru cases that incubation periods could top 50 years.
A professor of pathology and a CJD expert at the University of Melbourne, Colin Masters, commented yesterday: "These new data reinforce our need to maintain vigilance over potential risks to the safety of Australia's blood supply, since it has now been demonstrated that vCJD can be transmitted by blood transfusions."
In an accompanying editorial, The Lancet stated: "Any belief that vCJD incidence has peaked and that we are through the worst of this sinister disease must now be treated with extreme scepticism."