Jonathan Simms, who contracted the fatal disease six years ago aged just 17, was given 12 months to live in 2001.

Speaking from his Highfield home in west Belfast last night, Jonathan's father Don revealed his son is no longer classed as terminally ill.

He also revealed he is battling a continual struggle with the medical profession to have blood tests carried out to determine whether the disease is still present in his son's body or whether it is located solely in the 23-year old's brain.

The disease - the human form of BSE - starts in the stomach and rises to the brain.

Following a lengthy court battle, the Simms won the right three years ago to have Pentosan Polysulphate (PPS) infused to his brain.

Don now wants tests carried out to determine whether vCJD remains in his son's body.

He said: "If a plumber came to your house to fix a leak, the first thing he would do is turn off the water supply.

" With Jonathan, we want to know whether vCJD is still in his body and if it is, I believe we can tackle it with Pentosan.

"If we can abolish vCJD from his body by using PPS in the blood stream then we can say with some certainty that it could be abolished in the brain.

" Jonathan is not being treated for the disease in his body, which is where it originated, and in my view it can still be there.

"If it's coming from his body it needs to be treated in his body.

"We can use Pentosan against it and if we did this then after a period of time we could re-test his blood to see if it is still in his body.

" If it's not there we can say we have cut the supply right off. The way in which we can do this is via a very simple blood test which I have been requesting for the last three years. But the entire health authority across the UK has stopped this from going ahead."

Don revealed three independent examinations of scans of Jonathan's brain concluded there has been no further brain wastage from June 2004 up to the present day.

He said: "This would lead me to conclude that Pentosan, which has been infused in Jonathan's brain since 2003, has had a beneficial effect. I have also asked if these scans can be analysed in Northern Ireland."

When Jonathan was diagnosed with vCJD, the father and son promised each other they would do all they could to fight the disease.

Describing his son's speech as "intermittent", he said: "We hear words on occasion and he does show signs of pleasure and displeasure.

" If someone goes from his room to the kitchen or the dining room and they are not in full view of Jonathan, he will shout out because he likes the noise around him, he likes company."

But Don admits that his eldest son's medical condition has impacted on the rest of the family.

He said: "It has had a psychological effect on the whole family, especially Jonathan's younger twin brothers who are 15. As for my wife Karen and myself, we continue to do the best we can."