vCJD may have infected far more people than previously thought

May 21 2006

Scientists at the National CJD Surveillance Unit at the University of Edinburgh say that thousands may be infected with variant Creutzfeldt-Jakob Disease (vCJD) without showing signs or symptoms.

The researchers carried out tests on more than 12,000 tissue samples from tonsils and appendices removed in operations between 1996 and 1999, all from patients aged 20 to 29.

In the process they found that a far larger portion of the human population could be carrying the infection and could pass it on via blood transfusions or contaminated surgical instruments.

Two of those samples contained prion proteins which indicates vCJD infection and were taken from people with a genetic make-up that had not previously been thought susceptible to the disease.

The researchers warn that there is the possibility that a second wave of cases could emerge years or even decades after the first if the incubation period in the new group of infected people is longer.

To date 161 people in the UK have succumbed to the incurable infection which slowly destroys the brain until death becomes inevitable.

Each case so far identified has occurred in people carrying the methionine MM genotype, which is present in 40 per cent of the population.

But the two new cases were found in tissue samples with the valine VV genotype, which is present in only 10 per cent of the population and as no one with this genetic make-up has developed the disease, it raises the possibility that they may very well be asymptomatic carriers who could pass it on via blood.

The other 50% of the population carry the methionine/valine MV genotype.

The experts say the fact that both the tissue specimens turned out to belong to the rarest of the genotypes in the population was a surprise and could indicate a very long incubation period or that the disease never develops but remains in a carrier state with the potential to infect others.

Although this new evidence may well rekindle fears of a larger epidemic, others warn that it is important to be cautious in interpreting the results.

Since the initial discovery of vCJD in the United Kingdom a decade ago, there has been concern about the ultimate extent of the epidemic.

Fortunately the magnitude of the epidemic at present seems to match the lower limit of the early estimates, with 161 definite or probable cases in the UK.

After the widespread exposure to Bovine Spongiform Encephalopathy (BSE) in the 1980s, it is questionable why there have not been more cases of vCJD.

The answer may very well be that more are infected but the infections as yet have not appeared or may never appear as the incubation period may be decades.

Estimates of the eventual size of the human epidemic have been wide ranging from hundreds to thousands of people infected, however most scientists believed that 10 years after the first human cases were identified, the worst was over.

The findings will intensify the pressure on the Government to change the rules for post-mortems to include tests for vCJD, which cannot be detected until after death.

Drug companies are presently racing to develop a screening test which could be used for blood donors to detect the presence of the disease before symptoms develop.

But this could raise ethical problems over the detection of a condition for the protection of others but which has no treatment.