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Faster methods sought to detect mad cow disease; The search is on for quicker screening tests for mad cow disease as the USDA steps up its cattle surveillance program.

Faster methods sought to detect mad cow disease;
The search is on for quicker screening tests for mad cow disease as the USDA steps up its cattle surveillance program.

June 10, 2001, Star Tribune (Minneapolis, MN) by Joy Powell

At a high-security laboratory near Paris, a U.S. veterinarian worked side by side with French scientists. Wearing white gowns and masks that covered their mouths and noses, they peered through plastic face shields at the deadly brew in front of them.

In a well on a tiny plate, a solution had turned bright yellow. That change signaled the presence of infectious prions _ the warped brain proteins that cause mad cow disease.

The veterinarian, S. Mark Hall, was on a mission in Europe this spring to find a faster way to screen U.S. cattle for bovine spongiform encephalopathy (BSE), commonly called mad cow disease.

Faster methods are needed because the U.S. Department of Agriculture (USDA) is stepping up testing of slaughtered cattle for BSE. Hall, who heads the pathology section at the National Veterinary Services Laboratories in Ames, Iowa, is leading the search for new methods.

BSE was first discovered in Britain in 1986. In the past two years, wider screenings of cattle have detected BSE in France, Germany, Ireland and other nations. The scare is leading the United States to double the number of slaughtered cattle that will be tested this year. About 5,000 sick cows will be targeted.

"We're working hard to make sure that we test an adequate number of cattle in this country," Hall said after his European trip. "Essentially, we'll be using what is the best test and most cost-effective method for detecting the presence of BSE."

The race is on because mad cow and the human form of the disease are always fatal. More than 100 people, mostly in Britain, have died of variant Creutzfeldt-Jakob disease, is believed to come from eatingtainted beef.

With an incubation period that could exceed 40 years in humans, nobody knows how many other people could develop the disease. Once symptoms appear, death follows, usually within months.

If BSE is diagnosed in the United States, the nation's $175 billion beef industry would be crippled and world trade balances disrupted. Elsewhere in the world, the disease has led to millions of cattle being destroyed and billions of dollars being spent.

"If you want to stop the crisis, you have to be able to give a guarantee that no dangerous cattle will enter into the food chain," said Jean-Philippe Deslys, a leading French scientist who developed a test that detects BSE prions.

Dissecting brains

Hall is a tall, bearded scientist with a Ph.D. in veterinary pathology from Oklahoma State University. He is an expert in pathology _ the microscopic examination of tissues for lesions or abnormalities. He's also trained in testing methods based on chemistry.

Because of Hall's knowledge in both areas, his boss chose him to scout for new tests to be used in Ames, which is the nation's central diagnostics site for BSE and other diseases that could affect the U.S. economy.

Five weeks ago, Hall traveled from Iowa to France, Belgium, Austria, Germany and Switzerland to evaluate BSE testing methods.

On a sunny morning in early May, he arrived at France's Atomic Energy Commission in the Paris suburb of Fontenay-Aux-Roses. The massive fortress of white and gray buildings is a heavily guarded national defense facility.

Hall was escorted to the medical research laboratories, where he met with Deslys, the pioneer in prion research. Deslys told Hall about his data and the French test. Over the next two days, Hall was trained how to run the test.

He and other scientists weighed samples dissected from softball-size cattle brains. They treated the samples with an enzyme that stripped away normal prion proteins, leaving only the misshapen prions that eat away brain tissue and leave sponge-like holes.

Using a special solution, the scientists concentrated the rogue prions in a well on a 3-by-5-inch plastic plate. They added an antibody that clings to prions, immobilizing them, and then added a second antibody. After more processing, the mixture glowed yellow.

"It's very impressive," Hall later said of the highly sensitive French test, which is marketed by a California-based company, Bio-Rad Laboratories.

He also evaluated other tests, including one developed by Prionics AG of Switzerland. He and a colleague will soon visit Ireland to review a test developed by Enfer Scientific Ltd. of Ireland and marketed by Abbott Laboratories of Abbott Park, Ill.

Hall is mum on whether he favors any one test, saying that even the slightest nod from him could affect stock prices. Each test uses a different method, but all examine tissue for prions.

Prion-diagnosing tests are used after symptoms appear during late stages of the disease in humans, whose tonsils are tested, or on brain and spinal tissue tissue taken from dead animals.

No one has yet developed a blood test that can detect the presence of the disease in its early stages. Around the world, companies are scrambling to develop one.

Ground zero in Iowa

Unlike the sprawling atomic research center in France, Hall's home base is a cramped diagnostics laboratory tucked into a strip mall in Ames. In leased space that once was an old welding shop, Hall runs a section that diagnoses prion-related diseases in animals.

USDA officials are asking Congress for up to $548 million to build a new, consolidated center. Until then, the pathologistsand other scientists are scattered throughout Ames in dozens of buildings.

Day after day, the pathologists examine brains from sheep, cows, deer and elk. They first "fix" the soft, pink brains for five days in a formulin solution that hardens them to a gray, rubbery consistency. Part of the brain stem, where prions typically concentrate, is removed and sliced as thin as onion skin. It's mounted on slides, stained and studied under a microscope.

The pathologists are hunting for holes in the brain tissue that accompany prion diseases, called transmissable spongiform encephalopathies (TSEs). BSE is one of them.

As their workload increases, American scientists are turning to Europe for a faster testing method in which ground brain samples are mixed in a solution, without the five-day "fixing" process or use of a microscope. The solution simply changes color if rogue prions are present.

Because European tests have been known to produce false positive results, they must be verified by "gold standard" tests now used in Ames, said Art Davis, chief of the pathobiology laboratory.

Though testing is being ramped up, the United States lags far behind European countries that are testing all slaughtered cows older than 30 months before they enter the food chain. Prions accumulate over time and are easier to detect in older animals. And older cows might have been fed contaminated feed before governments banned use of meat and bone meal as a protein supplement.

In 11 years _ from 1990 through March 31 _ the United States tested 12,341 slaughtered cattle for BSE.

By comparison, France has tested more than 500,000 slaughtered cows older than 30 months since Jan. 1. Cows that are 30 months or older are incinerated if not tested to prevent them from getting into the food chain.

From July 1999 to December 2000, France tested about a smaller number: 50,000 "downer" cows that couldn't walk or were considered emergency slaughters because they were sick. The incidence of BSE was 1.5 cases per 1,000 sick cows.

Rather than testing by age, the United States is targeting downer cows that can't walk at slaughterhouses and others exhibiting neurological problems.

More veterinarians and animal health technicians are being recruited to spot sick cattle, said Linda Detwiler, who heads a BSE working group for the USDA's Animal and Plant Health Inspection Service in New Jersey.

The USDA doubled the number of cows tested last year and will double it again this year. But the agency has not determined how many will be tested in 2002, she said.

There's no indication that BSE is in the United States, which has taken measures to keep the nation free of the disease. But some experts say testing hasn't been widespread enough to detect the disease. Among those calling for more testing is Stanley Prusiner, who won a Nobel Prize in 1997 for his discovery and research of prions.

In Ames, the workload is already increasing for the pathologists, who don't discount the possibility they may diagnose BSE in American cattle.

"If it's here," said Davis, the pathobiology chief, "we've got to look more. We have to do what we can to find it. That's our job."

_ Joy Powell is at jpowell@startribune.com

Prions

Abnormal prions can cause infectious diseases of the brain in animals and people. The disease is given a different name according to the species:

Humans: Creutzfeldt-Jakob disease (CJD)

Cattle: Bovine spongiform encephalopathy (BSE)

Sheep: Scrapie and possibly BSE

Deer/Elk: Chronic wasting disease (CWD)

The abbreviation TSE, for transmissible spongiform encephalopathy, is used as a general term for the family of diseases.

Prion diseases are transmissible between species and bring about the slow degeneration of the central nervous system, which inevitably leads to death. A long period elapses between infection and the appearance of the first clinical symptoms. Typically, it is two to four years in sheep, three to six years in cattle and more than 10 years in humans. Once the symptoms appear, death follows within months.

Source: University of Zurich and Prionics AG, Switzerland, May 2001.


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