Surveillance Vs. Safeguards

BSE prevention measures are quickly evolving.

U.S. producers are quickly learning that even though they and USDA had created the safest food supply in the world, some cracks are showing up in the glaring light of international scrutiny.

Policies and regulations that made perfect sense before the first U.S. case of bovine spongiform encephalopathy (BSE) suddenly appear haphazard, deficient or illogical.

For instance, even though DNA confirmed the infected cow was from Canada, she was discovered here. Worse, by the time her test came back positive two weeks later her carcass was in eight states and Guam.

So, why was a cow tested for BSE passed into commerce before results were known?

The decision to ship or hold carcasses before test results are known was left up to plant management, says Lisa Ferguson, senior staff veterinarian for USDA's Animal and Plant Health Inspection Service (APHIS) of the previous policy. “Any that had classical clinical symptoms would have hopefully been condemned,” she says.

USDA modified this policy in a flurry of rules it pronounced a week after the BSE news broke. Inspectors can no longer mark cattle tested for BSE as “inspected and passed” until a negative confirmation is received. Also, downer cattle are now prohibited from slaughter. Instead, they go to the renderer.

Apparently, the infected cow was non-ambulatory due to a calving injury but showed no BSE-associated symptoms. Ken Petersen of the Food Safety Inspection Service says veterinarians identified clinical symptoms of neurological disorder in 130 animals tested out of 19,777 head in 2002.

USDA conducted BSE tests on 20,277 brain samples last year, 75% of those on non-ambulatory cattle. What are the odds the infected cow, if mobile at harvest, would have been tested? Or, that she would have been among downers harvested last year that weren't tested? What are the odds one like her has slipped through?

“Very low,” Ferguson says. “First, the Harvard Risk Analysis demonstrates that even if introduced, the likelihood of spreading is very low. Also, there's the fact we've done surveillance since 1997. Can we positively assure that didn't happen? No. Do we think it's likely it has happened? No we don't.”

For one thing, APHIS's “national approach to BSE surveillance” includes targeting the cattle population at most risk for BSE to be among the sample group tested. That means animals with clinical BSE symptoms, followed by downers.

For another, USDA began implementing BSE prevention measures 15 years ago. This included a ban of live ruminants and ruminant-derived products from countries where BSE was known to exist in native cattle.

Current surveillance testing is based on the Harvard Risk Analysis. The statistical model is designed to find one BSE case in a million, based on 12,500 samples. USDA could conduct only 433 tests/year and meet the standards set by the World Organization for Animal Health (OIE).

So, the testing USDA had been doing exceeded OIE recommendations. Even before the U.S. case, USDA says it planned to double the number of cattle tested for BSE this year to more than 40,000 head.

New Testing Regulations?

Would USDA consider testing all cattle at harvest? Ron DeHaven, USDA chief veterinary officer, says USDA feels “very comfortable” about its program, given what's known about the disease and the U.S. exposure to it. He adds, however, that the BSE incident makes it “prudent” to examine the current program and make needed changes.

“One of the things we're looking at is additional testing, and what populations of cattle would be appropriate for that additional testing,” he says.

Testing is a prickly issue. Keith Belk, a Colorado State University meat safety expert, says no amount of testing can ensure a product is safe. “Detecting for disease prevelance is certainly a reason to test. However, more important and scientifically valid reasons to test are to verify the effectiveness of the firewalls put into place to prevent the occurance of risk,” he says.

Plus, what do you test? BSE is thought to have an incubation period of three to six years before either clinical symptoms are visible or it's detectible by current tests. European Union (EU) countries are testing cattle older than 24 or 30 months of age, depending on the country. Japan tests every head at harvest.

Next, which test to use? USDA employs an immunohistochemistry (IHC) test, which OIE considers the gold standard. But it's impractical for high-volume testing. Other countries use rapid tests to screen animals, then confirm with the IHC test.

The IHC test identifies the effect of abnormal prions — the causative BSE infection agent — by detecting the brain damage they cause, says Jim Koziarz of Abbott Laboratories. Rapid tests identify the presence of abnormal prions.

“Consequently, the rapid tests can detect the presence of prions in cattle that exhibit none of the clinical symptoms we associate with BSE,” Koziarz explains.

Abbott is exclusive distributor of a rapid test developed by Enfer Scientific of Ireland, one of a handful available. All the rapid tests are relatively the same because all must attack the problem similarly, Koziarz says.

That means taking a brain sample, identifying it to the carcass, grinding it to release abnormal prions, centrifuging off debris, then pre-treating what's left with an enzyme that digests all proteins but the prion. From there, it's a simple Enzyme-linked Immuno-absorbant Assay (ELISA) using antibodies to detect the infectious agent. This can be done in less than four hours, about the same time that carcasses chill before fabrication.

The difference among the tests, Koziarz says, is user-friendliness and ability to mix into the production flow of a harvest facility.

Regardless of test type, if USDA moves to increase testing in a big way, it's not just flipping a switch. Notwithstanding the time involved with the IHC test, laboratory capacity to handle such volume is questionable.

That may be why USDA recently began accepting license applications for BSE rapid tests. Albeit, the fact that non-ambulatory cattle will no longer be going to slaughter will make it tougher to find and test members of this key risk population.

DeHaven says it could take up to a year or more to license rapid tests. USDA doesn't want to be caught needing such tests, then beginning the licensing process, he adds.

Even with rapid tests, Koziarz says it will take time to build and expand capacity. But he says, tests like Abbott's are scalable. In fact, the Enfer test is used in 13 countries. He estimates it could be scaled for widespread U.S. use within 12 months.

Plugging Related Gaps

Besides testing cattle, there's also the issue of enforcing the U.S. ban on feeding ruminant-derived protein (meat-and-bone meal) to other ruminants. Implemented in 1997, the ban is key to the nation's current BSE surveillance program. The problem is that compliance is a major question mark.

A 2002 General Accounting Office (GAO) report concluded the “FDA has not acted promptly to force firms to keep prohibited proteins out of cattle feed, and to label animal feed that cannot be fed to cattle.” In addition, the GAO report called FDA's inspections data “severely flawed” and left the agency “unaware of the full extent of industry compliance.”

Even if it's all under control these days, one must wonder how tight the system was before the report?

Also, why isn't USDA tracking down all Canadian cattle imports to the U.S. like it did British imports in 1989 when BSE was discovered in the UK?

“This situation is different,” Ferguson says. British imports represented significantly higher risk due to the absence of ruminant-to-ruminant feed regulations at that time, she says. Also, “we didn't have the knowledge in place that we have now.”

Back then, little was known about BSE or how beef industries in BSE-affected countries operated. Since U.S.-Canada trade is integrated and shares many firewalls, USDA is more familiar and comfortable with the risk of Canada's cattle population, she adds.

No doubt there will likely be other changes in policy as the BSE investigation unfolds. There's also little doubt about who will wield the most pressure for change.

“Scientists will discuss what is appropriate, given the likelihood of risk,” Belk says. “Ultimately it will end up in the politicians' court. It becomes an issue of public acceptance of risk.”