Doubt cast on BSE-CJD link

The brain of a CJD patient

The link between "mad cow disease" and vCJD - commonly thought to be its human equivalent - has been disputed by an expert.

Dr George Venters, a consultant in Public Health Medicine in Lanarkshire, Scotland, claims evidence linking the two conditions is weak.

The variant form of CJD may simply be a rare type, which existed long before the BSE epidemic in cows, but was simply not diagnosed and catalogued properly until the 1990s.

If his theory is correct, it would mean victims of the condition did not get it by eating infected meat.

I believe the evidence now available casts serious doubts on the case for a causal link

Dr George Venters

But other CJD experts say the evidence is strong enough to firmly suggest humans contract vCJD by eating meat from cattle with BSE containing infectious prion proteins.

Dr Venters bases his opinion on the fact that the rate of growth in the number of confirmed cases is much less than might be expected from a food-borne source.

He suggests the rate of growth in the number of vCJD cases is more consistent with a previously misdiagnosed but extremely rare disease being found.

Advances in the detection and reporting of suspected cases through the CJD Surveillance Unit in Edinburgh could account for an apparent rise in the number of cases, none of which would have been officially recorded previously.

He wants a public debate on the evidence supporting a link between the two diseases.

Dr George Venters put forward the controversial theory

Speaking on BBC Radio 4's Today programme, Dr Venters said government policy should focus on "a more realistic appraisal of risk, addressing what is likely to happen rather than what is a frightening but increasingly less likely possibility".

He said: "Without doubt, general anxiety about so dreadful a possibility as BSE causing a similar disease in humans resulted in many workers involved with BSE and CJD having to reach precipitate conclusions in which public safety was rightly the prime consideration.

"I believe the evidence now available casts serious doubts on the case for a causal link between bovine spongiform encephalopathy and 'new' variant Creutzfeldt-Jakob disease.

"A particular problem is that when you have a food-born infection you expect the rate at which cases occur to run parallel to the rate at which the population is exposed to infection. That doesn't seem to be happening."

Public debate

vCJD cases don't occur in those countries that have not got BSE

Dr Phillip Monk

But Dr Phillip Monk, a consultant in communicable diseases who investigated a vCJD cluster in Queniborough, Leicester, dismissed the theory.

He told Today: "You only have to realise that vCJD occurs in countries like ours that have had high problems with BSE.

"vCJD cases don't occur in those countries that have not got BSE. The moment we relax our guard, we put people at risk again."

Professor James Ironside, from the CJD Surveillance Unit, also disagreed with Dr Venters' theory.

Professor Peter Smith said the link was beyond reasonable doubt

He said: "I think it is an interesting paper and it is always important to consider a range of arguments on this subject because there are huge numbers of uncertainties.

"But we do know from a number of studies done both here and in the States that the transmissible agent that causes BSE is the same as that which causes CJD and has also transmitted to other species including cats, wild cats and antelope in zoos.

"The most probable hypotheses for linking the numbers of species together is by food-borne exposure as was the case with BSE."

Professor Ironside added that the incubation period of the disease was significant and there had been a slight rise in the number of cases over the past 12 months.

Professor Peter Smith, chairman of Seac, the scientific body that advises the government on CJD, said the only way to prove the link between BSE and CJD would be to inject BSE-infected material directly into a human.

But he said: "The circumstantial evidence is beyond reasonable doubt now that BSE and vCJD are caused by the same infectious agent."