Mad cow disease 'breakthrough'

2005-08-29 09:28

Paris - The battle against mad cow disease and its human equivalent may soon be transformed by a new tool designed to detect the treacherous prion protein in the blood, scientists hope.

Bovine spongiform encephalopathy (BSE), as mad cow disease is called, and variant Creutzfeldt-Jakob disease (vCJD) are caused by a rogue version of a prion protein, PrPSc, which multiplies in the brain, eventually turning it spongy.

But efforts to roll back these two fatal diseases have been hampered by the absence of a simple, accurate way of telling whether a person or an animal is carrying PrPSc.

As a result, billions of euros (dollars) have been spent in Europe over the past decade to slaughter cows in a precautionary attempt to halt BSE. And there are fears that people with latent vCJD may spread the disease through blood donation.

At present, only post-mortem analysis of brain and lymph tissue is the guaranteed way to confirm the presence of PrPSc.

The solution would be a simple blood test that can be carried out while the person or beast is still alive. But levels of PrPSc in the blood are so tiny as to be undetectable, until now, by biochemistry tests.

That may change, thanks to work by Claudio Soto and others at the University of Texas.

The test-tube process

In a study published on Sunday in the British monthly journal Nature Medicine, Soto's team says it has devised a test-tube process that quickly and accurately identifies minute quantities of PrPSc in the blood.

The process is rather similar to polymerase chain reaction (PCR), famously used by police scientists to amplify tiny samples of DNA to produce the "genetic fingerprint" of a crime suspect.

Soto's method takes PrPSC and incubates it with the non-rogue PrP to create clumps of a new, telltale protein. To amplify the sample and thus boost the chance of detection, the clumps are broken up by soundwaves and the incubation process is resumed.

The process is 89% accurate in spotting the presence of the marker protein and, importantly, never returns a "false positive" (that the marker is there when in fact it is absent).

The test takes "around 48 hours, between 48 and 96 [incubation] cycles," co-researcher Joaquin Castilla said.

So far, the blood tested has come from lab hamsters which have been deliberately infected with PrPSc.

But the team is confident that the prototype technique is applicable to human blood too and, if confirmed effective, can be automated to handle large numbers of samples.

- AFP