The researchers say the 60-year-old man and his seven-year-old cat appear to have been infected by the same strain of Creutzfeldt Jakob's Disease.

The cat showed evidence of having contracted a new form of the feline version of BSE, FSE.

The man died in January 1994 after contracting a form of CJD known as sporadic CJD.

This is not the same as the new variant version of CJD linked to the BSE outbreak.

No known cause

Sporadic CJD has been around for many years and tends to affect older people.

It accounts for 85% of all CJD cases and no-one knows what causes it.

Prior to concerns about so-called mad cow disease, the majority of CJD cases were found in older people.

The new variant form was diagnosed after a number of cases were identified in young people.

The man was admitted to hospital in November 1993 with balance, visual and muscular problems.

Ten days later, he was unable to speak or follow simple commands.

Two weeks later, he lost the ability to swallow and by January 1994 he was dead.

Twitching

His neutered, female, short-haired cat first showed signs of infection in November 1993.

Sporadic CJD is not linked to BSE

It suffered episodes of frenetic activity and twitching of its body.

It was killed in January 1994 after developing muscular spasms and problems controlling its hind quarters and movement.

The cat usually slept on its owner's bed. The owner showed no sign of having been bitten by his cat and had "no unusual dietary habits".

It was fed on tinned cat food.

Normally, FSE is characterised by a gradual onset of behavioural problems leading to movement disorders.

However, in this case, the clinical features were different.

Protein prion

The researchers, from the University of Verona and the Istituto Zooprofilettico Sperimentale della Lombarida e dell' Emilia, say there was evidence of a protein prion in both the man and cat which is not normally present in FSE.

Writing in The Lancet, they say they do not not if infection was caused by the man or cat, by chance or by an unknown common source.

Ted Chandler, former president of the British Veterinary Association, called the case "fascinating".

It is rare for cat diseases to pass to humans

"It is another bit of the jigsaw puzzle about what is going on with these diseases," he said.

"The next big revelation will be what causes sporadic CJD."

He thought the man and cat had probably been infected by a common source since it was rare for diseases to pass from cats to humans in a similar form.

He thought it more likely that they had eaten the same infected food, but he did not rule out the possibility of other routes of infection, such as mosquitoes.

No BSE problem

He believed it was unlikely that beef was the cause since Italy has no previous cases of FSE and no record of problems with BSE.

There have been around 80 cases of FSE in the UK over the last seven years, but the numbers have fallen recently to around six a year because precautions were being taken by pet food manufacturers.

Mr Chandler said the new case would mean doctors would have to start checking all people with sporadic CJD to see if they had pets.