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鈥檚 a
straightforward approach many researchers assumed wouldn鈥檛 work鈥攑rimarily
because most proteins are filtered out by the kidneys and never make it into the
urine.
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However, Gabizon says this is partly a misconception鈥攕ome 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.
鈥淚t caught all of us by total surprise,鈥� says Adriano Aguzzi, a prion
researcher at the University of Zurich. 鈥淲hat this says is we know far less
about prion pathogensis than we realised.鈥�
Although the exact nature of the protein and the details of how it winds up
in urine aren鈥檛 known, Gabizon鈥檚 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鈥檛 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. 鈥淚f 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,鈥� 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? 鈥淭hat鈥檚 one of
the issues we鈥檙e grappling with at the moment,鈥� Hewitt says.