- The Washington Times - Sunday, May 25, 2003

Canadian health authorities have but one grisly way to stop mad cow disease: Kill all 150 animals at the Alberta ranch where a single, unsteady old cow was stricken.

That is because no simple diagnostic test is available for bovine spongiform encephalopathy in live animals.

“We can’t look for the agent that causes mad cow disease itself,” said Dr. Stephen Sundlof, director of the Food and Drug Administration’s Center for Veterinary Medicine. “The science hasn’t gotten us that far.”

Dr. Sundlof and others say an early diagnostic test for BSE would save money, time and healthy livestock, and would stifle the public alarm that mad cow triggers.

In the past two years, several potential live tests using blood, urine and nasal mucous have generated biotech buzz and inflated stock prices, but skeptical researchers and regulators say it may be years before an experimental method proves reliable.

“I’ll believe it when I see the test,” said University of Wisconsin microbiologist Judd Aiken.

“These diseases have an extended preclinical stage where there are no symptoms, and yet the animal has high levels of the infectious agent,” Mr. Aiken said. “It is exceedingly important to develop a test that will identify the disease earlier and keep [other] animals alive.”

Mad cow disease appeared in Britain in 1986 and spread to countries in Europe and Asia. It is thought to have been carried in cattle feed that included protein and bone meal from sheep or other mammals infected with otherspongiform diseases.

The cattle disease is linked to a brain-destroying human illness called new variant Creutzfeldt-Jakob disease. The human illness is believed to be spread by eating brain or nerve tissue from infected animals and has killed at least 132 persons, 122 of them in Britain.

No BSE has been found in U.S. cattle. The FDA outlawed feeding meat and bone meal from mammals to cattle, sheep and goats in 1997, the same year Canada issued a similar ban.

Canadian officials say the infected cow there may have been born before that ban, but they are not certain about its age.

Test results have cleared all other cattle in the original herd linked to the mad cow case, Canadian officials announced yesterday.

“The results from diagnostic testing on the first quarantined herd are negative,” said Dr. Laude Lavigne of the Canadian Food Inspection Agency.

“It means the incidence of BSE in Canada presently remains in one cow.”

The United States also prohibits imported beef and cattle from BSE-tainted countries, which now include Canada. However, the U.S. government tests just a tiny fraction of the millions of cattle processed annually, usually those that exhibit neurological symptoms. It takes eight days to obtain test results from the National Veterinary Services Laboratory in Ames, Iowa.

Other nations have far stricter rules, more labs and faster testing. In Britain, inspectors test the brains of all slaughtered cattle older than 30 months. Japan tests each of the 1.3 million beef carcasses it processes annually.

Both countries use a rapid screening process that detects whether an animal’s immune system generated antibodies to the disease. A positive test requires a second, more sophisticated test to confirm the infection.

Results usually are available within a day.

The Department of Agriculture is evaluating a 20-minute BSE strip test on brain tissue. The test is similar to a home pregnancy test. Its developers say it could be used by veterinarians at BSE-quarantined ranches, or by inspectors at meat-packing plants.

But nobody has won approval for a live spongiform test. That’s because researchers know little about the rogue proteins called prions that probably cause the diseases.

Proteins are large molecules that carry out a cell’s vital functions. The protein’s shape heavily influences the function.

For unknown reasons, one protein in brain and nerve cells misfolds, causing surrounding proteins to clump and inducing proteins in adjacent cells to misfold, too.

Over years, these dying cells create tiny holes and turn brain tissue spongy.

Some researchers think prions may be unusual viruses.

But unlike viruses, prions withstand ultraviolet light, ionizing radiation, sterilizing temperatures and chemical disinfectants.

Prions also don’t contain nucleic acid, which are the genetic building blocks for DNA and RNA. The absence of genetic material denies any prion vaccine or drug an obvious target to attack.

A live BSE test, researchers say, must work flawlessly on millions of animals every year. Even one cow with BSE can wreak havoc.

“You want a test that is very specific and sensitive,” said Robert Moeller of the University of California-Davis Animal Health and Food Safety Laboratory.

“What usually happens is that you get a diagnostic method that shows promise, but then it’s not reliable enough.”

Most such research is in Europe, where BSE is a greater threat. The effort that seems to have progressed the furthest is a blood test developed by Proteome Sciences of Surrey, England.

In April, Proteome signed a development agreement with IDEXX Laboratories Inc., a large veterinary-diagnostics company based in Maine.

Proteome predicts that its BSE blood test could be ready within 18 months. It would identify a specific lipoprotein in blood samples from BSE-infected cattle years before the animals show disease symptoms.

However, scientists with the International Office of Epizootics, the Paris-based animal health agency, say that the lipoprotein is just one biomarker for neurodegeneration and may not be precise enough.

In Italy, researchers who found prions in olfactory sensors leading to the brain are developing a live test that looks at prions in the nasal mucous of infected cattle.

In 2001, researchers at Jerusalem’s Hadassah University Hospital were developing a urine test that can spot prions, but other scientists say it’s not clear whether prions pass though the kidneys.

German researchers are working on a 15-minute blood-screening test that uses infrared spectroscopy to make a molecular profile of a blood sample.


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