The worst of human BSE infection may be over, according to scientists monitoring vCJD.

The National CJD Surveillance Unit said the number of people dying from the human form of mad cow disease each year is falling.

But in a study published in medical journal The Lancet, the team warned that it is too early to conclude that vCJD is in permanent decline.

Later on Friday a report will be published into an incident in which 24 patients at Middlesbrough General Hospital were exposed to surgical instruments used on a patient later found to have vCJD.

Incurable disease

According to the National CJD Surveillance Unit the disease has taken 122 lives in the UK since it emerged in 1995.

Eight people thought to have the incurable disease are still alive.

Last year 17 people died, compared to 20 in 2001 and 28 in 2000 - when the disease reached its high point.

There has been one provisionally recorded death so far this year.

Incubation period

Scientists have found it difficult to predict how many people will die of vCJD, because there is no accurate diagnostic test.

There is also no way of telling how long the disease is present in the body before it strikes.

Although the disease appears to be declining, scientists point out that its incubation period may vary from one individual to another - as has been observed in mice.

They also warn that future cases may also arise from secondary transmission such as contaminated surgical instruments or donated blood.

Dr Robert Will, head of the Surveillance Unit, said: “That mortality is no longer increasing exponentially is encouraging.

“However, to conclude that the epidemic is in permanent decline would be premature.”

His colleague Professor James Ironside agreed that it was possible that the number of vcJD cases could climb again.

He told the BBC: “There is evidence from other studies to indicate that there are differences in genetic susceptibility that do not allow us to say with certainty that the problem is over.”

Brain biopsy

In Middlesbrough the report will look at the circumstances surrounding the use of surgical instruments on 29 people after they were first used on the vCJD patient.

Five of the group were told they were at no risk.

The remaining patients have been critical about the handling of their case, claiming that they were left waiting for news about how great a risk they were at.

The surgical instruments concerned were first used for a brain biopsy on a woman who, at the time, was not suspected as suffering from sporadic CJD.