A study suggests that 3,800 Britons could be harbouring the human form of BSE. BBC News Online examines the claims.
vCJD is a fatal brain disease
What is vCJD?
Variant CJD or vCJD is the human form of BSE. It first emerged in 1995 and has so far claimed 141 lives in the UK.
The disease, which affects the brain, is believed to have passed from cattle to humans through infected meat.
It causes personality change, loss of body function, and eventually death. It is thought to be caused by rogue proteins called prions.
Doctors are testing a number of experimental treatments. However, as yet there is no cure.
What does this latest study say?
Scientists at Derriford Hospital in Plymouth and the National CJD Surveillance Unit in Edinburgh have carried out tests on 12,674 appendix and tonsil samples.
These are part of the lymphatic system and are probably where prions are most likely to accumulate.
The samples had been taken after 1995 from patients between the ages of 20 and 29 - the highest risk group for vCJD.
They found signs of vCJD in three of these samples.
They extrapolated these figures for the entire population and calculated that on the basis of this study 3,800 people could be harbouring the disease.
Are the figures reliable?
The figures are not reliable. Even the researchers who carried out the tests say the findings must be interpreted cautiously.
One of the problems is that appendix samples don't always show up vCJD prions.
Another problem is that these prions were only found in three samples and then the figures were extrapolated to give a population-wide figure.
In addition, scientists don't know at what stage in the disease these prions are found in tissue.
This lack of knowledge is hampering efforts to make an accurate prediction on how many people may be infected.
A recent study by researchers at Imperial College London suggested the disease would claim no more than 540 lives.
The government has set up a national tissue archive which is in process of collecting 100,000 tonsil and appendix samples.
Scientists hope that by carrying out tests on such a large number of samples they will be able to come up with a more definitive figure for vCJD infections.
Nevertheless, some experts believe the number of people dying from the disease is levelling out and may even be declining.
At its peak in 2000, the disease killed 28 people. That dropped to 17 in 2002 and 18 last year. So far this year, two people have died from vCJD.
What are the risks of contracting vCJD now?
Tight rules have been introduced to ensure that BSE infected meat does not enter the UK food chain.
The focus now is on trying to reduce the risks of one person transmitting the disease to another person.
For instance, white blood cells have been removed from all blood used for transfusions since 1999.
This followed advice that if there was any risk of the disease being transmitted through blood, it was most likely to be found in these cells.
Blood products, such as clotting agents, are now only made using plasma from the United States.
Children born from 1996 onwards now only receive plasma that has been imported from the US.
The government recently banned people who had a blood transfusion after 1980 from donating blood.
It followed reports that one man who died from the disease may have caught it from a transfusion.
The Department of Health is spending £200m on improving its procedures for decontaminating surgical instruments, to reduce any risk of the disease being transmitted in this way.
As yet, there is no clear evidence that vCJD can be transmitted through contaminated blood or surgical instruments.
However, these steps have been taken as a precaution.