If you've got vCJD, would you want to know ?

If you've got vCJD, would you want to know ?

July 21, 2001 New Scientist by Greg Miller

A URINE test for mad cow disease and its human equivalent has been devised by scientists in Jerusalem. If the test works, it will offer a simple way to spot variant CJD and BSE in live patients and animals.

So far, examining brain tissue after death is the only way to get a definitive diagnosis. The new test would make it easier to gauge how many individuals are infected with vCJD, as health officials could anonymously test the population to come up with more accurate estimates of the size of any epidemic. Vets could do the same to spot BSE in cattle. You would also be able to screen blood donors and surgery patients for vCJD, allaying fears that the infection might spread through blood transfusions or contaminated surgical instruments.

The urine test, developed by Ruth Gabizon and colleagues at Hadassah University Hospital, uses antibodies that bind to prion proteins. It's a straightforward approach many researchers assumed wouldn't work - primarily because most proteins are filtered out by the kidneys and never make it into the urine.

However, Gabizon says this is partly a misconception - some proteins are small enough to slip through the filter. The version of the prion protein picked up by her test weighs in just under the limit.

Gabizon thinks the protein probably originates in the brain, then finds its way into the blood in very low concentrations. She speculates that her test works where antibody-based blood tests have failed because the kidneys concentrate the protein in urine, making it easier to detect.

"It caught all of us by total surprise," says Adriano Aguzzi, a prion researcher at the University of Zurich. "What this says is we know far less about prion pathogensis than we realised."

Although the exact nature of the protein and the details of how it winds up in urine aren't known, Gabizon's preliminary results look promising. She has identified prion infections in hamsters, cows, and humans with an inherited form of CJD. Her results will appear in a future issue of the "Journal of Biological Chemistry".

Before the test can be used widely, though, it will have to undergo extensive trials to work out how sensitive it is. You would need to ensure the test doesn't throw up false positives but is able to pick up infections early in the incubation period, says Christl Donnelly, an epidemiologist at Imperial College School of Medicine in London. "If you come up with few positives, you need to reassure yourself that you only have a few cases, as opposed to a bunch of people who are about to become cases," she says.

Even if the new test clears all these hurdles, deciding how to use it will involve tackling some sticky ethical questions, says Patricia Hewitt, head consultant in transfusion microbiology for the British National Blood Service. For instance, should prospective blood donors be notified if they test positive for CJD, given that there are currently no treatments available ? "That's one of the issues we're grappling with at the moment," Hewitt says.


