'Everyone at Risk from Mad Cow Disease'
By John von Radowitz, Science Correspondent, PA News
No one is immune to the human form of mad cow disease, variant CJD, new research suggests today.
Some people whose genetic make-up normally acts as a barrier against infection may ultimately develop a different and so-far unrecognised type of disease, it is claimed.
Scientists have shown that individuals with a pair of genes known as MM about a third of the population acquire vCJD relatively easily.
No one with a different paring, VV, has been known to suffer the disease.
Then in August it emerged that a patient from a mixed MV genetic group had been infected with vCJD from contaminated blood, without showing any symptoms. Just over half the population has the MV pairing.
The news sparked fears of a mad cow disease timebomb in the population, with thousands of people unwittingly carrying the brain disease on a long incubation fuse.
Now experiments on mice by British and Australian scientists have increased the uncertainty still further.
They suggest that even people with the highly resistant VV genotype might be at risk, though it would probably take them longer to become ill.
If they did develop symptoms, they could be quite different from those normally associated with vCJD.
Variant CJD (Creutzfeldt-Jakob Disease) emerged from the cattle disease BSE (Bovine Spongiform Encephalopathy) spreading to humans via infected beef.
It has been linked to 146 deaths in Britain, and causes a specific set of symptoms and changes in the brain.
Classic, or sporadic CJD, is from the same group of diseases spread by defective prion proteins but has a very different pathology and is not associated with eating contaminated meat.
The scientists, led by Jonathan Wadsworth at University College London, carried out tests on mice engineered to carry human genes.
They showed that the V gene severely restricted the propagation of both BSE and vCJD prions.
But the results indicated that it was possible for mice to develop a novel form of the disease. It also affected the brain, but produced a different pattern of damage from any seen in known versions of the illness including variant and sporadic CJD.
The researchers wrote in the journal Science: While caution must be exercised extrapolating from animal models, even where, as here, faithful recapitulation of molecular and pathological phenotypes is possible, our findings argue that primary human BSE prion infection, and secondary infection with vCJD prions by iatrogenic routes (through medical procedures) may not be restricted to a single disease phenotype.
None of the affected mice in the study developed visible symptoms. But the scientists pointed out that laboratory mice only had a two year lifespan, which may be less than the diseaseรขโฌโขs incubation period.
Dr Rudy Castellani, director of neuropathology at Michigan State University Clinical Center in the USA, said: The most alarming point raised in this paper is the experimental evidence that there may be types of vCJD lurking in the population, unrecognised as BSE-associated CJD