February 01, 2004

 

 Washington state dairy cow nation's first case of BSE - February 1, 2004

 
Washington state dairy cow nation's first case of BSE
Agriculture Department investigation leads to Canada, new safeguards imposed

The first case of bovine spongiform encephalopathy in the United States was confirmed Dec. 25, 2003, in a nonambulatory dairy cow slaughtered in Washington state. The infected animal was discovered as part of the government's policy to routinely test downer cattle for BSE, which has been linked to new variant Creutzfeldt-Jakob disease, a fatal neurologic illness in humans.

With the news on Dec. 23 that brain samples from a Washington cow had tested positive for BSE at the Department of Agriculture's National Veterinary Services Laboratories in Ames, Iowa, numerous countries began prohibiting imports of U.S. beef products.

In the wake of the discovery, the Agriculture Department announced that it was implementing a national animal identification system to track animal movement. "USDA has worked with partners at the federal and state levels and in industry for the past year and a half on the adoption of standards for a verifiable, nationwide animal identification system to help enhance the speed and accuracy of our response to disease outbreaks across many different animal species," Agriculture Secretary Ann M. Veneman said Dec. 30.

Veneman also ordered U.S. slaughterhouses not to process nonambulatory or "downer cattle" and to adopt processing techniques to prevent contaminating meat with bovine nerve tissue. Moreover, the skull, brain, trigeminal ganglia, eyes, vertebral column, spinal cord, and dorsal root ganglia from cattle more than 30 months of age cannot be used for human food; the use of small intestine of cattle of all ages is also prohibited.

The 6-and-a-half-year-old Holstein was part of a 4,000-dairy-cow operation in Mabton, Wash. Suffering from paralysis thought to be a complication of calving, the cow was slaughtered Dec. 9.

As part of the national BSE surveillance system, brain samples were sent to Ames, where histologic and immunohistochemical tests detected the presence of the degenerative brain disease.

Samples were flown to Central Veterinary Laboratory—the BSE world reference laboratory—in Weybridge, England, on Dec. 23 for final confirmation, which was announced Christmas Day.

Even before the laboratory verified the diagnosis, U.S. government and cattle industry officials were informing the public about the safety of American beef, along with the relatively low risk BSE poses to humans.

"Despite this finding, we remain confident in the safety of our beef supply," Veneman said as the nation headed into the holiday season. "This is an animal disease challenge, not a food safety problem," echoed J. Patrick Boyle, American Meat Institute president.

But as a precaution, the USDA Food Safety and Inspection Service issued a recall on Dec. 23 of some 10,000 pounds of raw meat distributed by Vern's Moses Lake Meats in Washington state, where the infected cow was processed.

Since the infected cow's brain, spinal cord, and other tissues most likely to contain the infectious BSE agent were not processed, the recalled beef presents "essentially zero risk to consumers," said Dr. Ken Petersen of the Office of Field Operations at FSIS.

Although the single case of BSE hasn't depressed beef consumption in America, the economic fallout won't be fully realized for several months, according to AABP President Mark F. Spire. The cattle industry must contend with rising production costs, declining beef prices, and the loss of foreign markets. "We have a beef industry that is going to be economically stressed," Dr. Spire predicted.

The Harvard Center for Risk Analysis released a study that concluded BSE has little chance of becoming established in the United States. Prohibitions on imports of European ruminant products, surveillance, and a feed ban were cited as effective measures for guarding against the disease (see JAVMA, Feb. 1, 2002, page 279).

Dr. William D. Hueston, America's leading expert on BSE, had hoped a U.S. cow would never be diagnosed with the "insidious disease." But he had been preparing for such a contingency for more than a decade.

When the disease was identified in 1986 in Great Britain, then spread to a growing number of countries, Dr. Hueston argued that the United States must be prepared.

Now that BSE is here, the director of the Center for Animal Health and Food Safety at the University of Minnesota is "thrilled" that the nation was as prepared as it was with systems to prevent, control, and detect the disease.

"When I compare the U.S. to other countries around the world, the U.S. took that preemptive strike of the feed ban in 1997 in the face of a lot of opposition," Dr. Hueston said, referring to the prohibition on using ruminant feed containing animal protein.

"I have been pleased to see that, over time, we have incrementally strengthened the protections (against BSE) in the United States," he added.

At press time in late December, the infected cow had been traced to a herd of 74 dairy cattle that entered the United States in August 2001 from Alberta, Canada. American and Canadian officials were working to verify the origin of the cow. A second shipment of eight cows from the herd also entered the country.

Government officials are confident that most of the animals are still alive. They should all be located quickly, because records are kept on dairy cattle.

In the meantime, the Washington herd that the infected Holstein was part of was quarantined. And while the USDA had made no decision on the disposition of the herd, any cattle that die on the farm will be tested for BSE.

The infected Holstein's age offers a clue as to how she might have contracted BSE. Records show the cow was born in April 1997, meaning she was born prior to the implementation of the August 1997 ban on ruminant feed containing animal protein in North America. That practice has been identified time and time again as the primary means by which BSE spreads.

"The age of the animal is especially important, in that it is a likely explanation as to how this animal would have become infected," explained Dr. Ron DeHaven, chief veterinary officer for the USDA.

The cow had three calves while in the United States. One died shortly after birth, another remains with the Washington herd, and her most recent calf is currently commingled in a herd of some 460 young bull calves, all around 30 days of age. That group is under a hold order pending completion of the USDA's epidemiologic investigation.

Maternal transmission of BSE is rare. Nevertheless, the animals are being sequestered to preserve public and international confidence in the health of the U.S. cattle herd.


— R. Scott Nolen

USDA