Fewer Britons may have the human form of mad cow disease than previously thought, a new study suggests.

It's not known how many people might have eaten infected meat and carry the abnormal prions that cause both BSE (bovine spongiform encephalopathy or mad cow disease) and its human equivalent, known as Creutzfeldt-Jakob disease (CJD).

Since 1995, there have been 168 definite or probable cases of the fatal, brain-wasting disease among people in Britain, according to the country's Health Protection Agency.

Based on those numbers, scientists estimated another 10 to 190 cases of variant CJD, one of two types of the disease, to appear over the next ten years.

Creutzfeldt-Jakob disease

What is Creutzfeldt-Jakob disease?

CJD is a disease caused by protein-like particles called prions. These attack the brain, killing cells and creating gaps in tissue. The disease is always fatal. There are two types of CJD: classical and variant.

Who gets it?

Anyone can potentially contract CJD.

Classical CJD occurs in the general population at a rate of about one case per million people per year throughout the world. In Canada, about 30 cases of classical CJD are diagnosed each year.

Source: Health Canada

But in this week's issue of the British Medical Journal, researchers suggest that the actual prevalence of the disease in the British population might be much lower.

"It may be that we have seen the worst of vCJD already, although we need to keep vigilant and implement appropriate public health measures to prevent any possible secondary spread of disease," Dr. Jonathan Clewley, an expert on vCJD at the Health Protection Agency, said in a news release.

"Estimating the prevalence of people who are carrying vCJD unknowingly is important in guiding our public health response to this disease and ensuring all necessary precautions are taken to reduce this risk of further transmission of the agent through surgical operations and other health care settings."

Tests on 63,007 tissue samples from people of all ages who had their tonsils removed between 2004 and 2008 at hospitals throughout England and Wales showed no evidence of the abnormal prion protein in any of the samples. Researchers had originally predicted the tissue samples would reveal up to 50 cases.

Tonsils are one of the places in the body that vCJD prions can accumulate.

The researchers said they need to complete their analysis of all of the samples before they can be confident about the low prevalence.

In a journal editorial accompanying the study, Maurizio Pocchiari, a neurology expert based in Rome, said it was unlikely that no one in the U.K. was incubating the disease, but that the small number of cases and diagnostic problems made accurate measurement difficult.

Pocchiari agreed with Clewley that precautionary measures, such as screening blood at blood banks, need to be maintained to avoid transmitting the disease.