Researchers at Edinburgh University believe they may have found the key to why younger people are more likely to develop the human strain of mad cow disease.

Sufferers of variant CJD (VCJD) are just 28-years-old on average and scientists have been keen to get to the bottom of why older people are not affected to the same degree.

Now, experts at the uni believe they have pinpointed a cell that assists in the spread of the disease but becomes less efficient with age.

And they hope the findings could improve diagnosis of the disease, or even assist in the development of a vaccine.

Researchers at the uni's Roslin Institute used mice to examine how the immune system interacts with a corrupted protein cell known as a prion.

Prions accumulate before spreading to the central nerve system, killing off brain cells and causing neurological disease. They have been widely linked to VCJD.

The researchers found that the prions essentially "hijack" specific cells in the immune system to multiply.

However, those cells were impaired in older mice, meaning the prions could not replicate and spread and the mice did not contract the disease.

Researchers said their study could explain why VCJD does not affect older humans to the same extent and why it occurs almost exclusively in young people.

Dr Neil Mabbott from the Roslin Institute said: "It has always been unclear why younger people were more susceptible to variant CJD and the assumption that they were more likely to eat cheap meat products is far too simplistic.

"Understanding what happens to these cells, which are important for the body's immune responses, could help us develop better ways of diagnosing variant CJD or even find ways of preventing prions from spreading to the brain. It could also help to create a vaccine."

Attempts to estimate the number of people carrying VCJD have relied upon identifying the presence of prions in tonsil and appendix samples collected during routine operations.

However, researchers involved in the current study said that, when prions were present in the brains of older mice, they were not always found in the expected tissues.

The team behind the research has warned that could suggest more people are infected than was previously thought.