October 01, 2003

 

 Canada wraps up BSE investigation - October 1, 2003

Posted on September 15, 2003
 
Canada wraps up investigation
Government officials implement new cattle processing restrictions, examine other policy changes

See also Veterinarians are on the front lines of BSE control  

Canadian officials wrapped up their investigation into the first case of bovine spongiform encephalopathy in a North American-born cow in late July after depopulating and testing more than 2,700 cattle and finding no additional cases of BSE.

"The investigation is effectively complete; where we are looking now is at the policy response," said Dr. Sarah Kahn, the director of the Animal Health and Production Division of the Canadian Food Inspection Agency.

The BSE case confirmed in May was the first in Canada since 1993, when officials identified BSE in an animal imported from the United Kingdom. In response to the most recent discovery, the U.S. Department of Agriculture banned imports of most ruminant products from Canada pending further investigation, as did dozens of other countries.

The investigation's findings will likely have far-reaching effects on BSE policies throughout North America, including international trade policies.

According to a report by a team of international BSE experts called in to review the Canadian investigation, the single case of BSE discovered in a 6- to 8-year-old Alberta cow in May was likely caused by exposure to BSE-contaminated feed early in the animal's life, prior to a 1997 ban on feeding ruminant meat and bone meal to other ruminants.

Members of the international team, comprising Drs. Ulrich Kihm and Dagmar Heim of Switzerland, Dr. William Hueston of the United States, and Dr. Stuart MacDiarmid of New Zealand, concluded that, given the likely source of infection, other North American animals may have been exposed.

"If this animal was exposed through the feed, which is the most likely explanation, it's very hard to make the case that this was the only animal exposed to the (contaminated) feed," said Dr. Hueston, the director of the Center for Animal Health and Food Safety at the University of Minnesota. "In all likelihood, there were additional animals exposed."

Though only a small percentage of the animals possibly exposed to contaminated feed prior to the '97 feed ban remain, Canadian officials have implemented new restrictions on the way ruminants are processed to prevent BSE-contaminated ruminant products from entering the food chain, at the recommendation of the international team.

The restrictions prevent specified risk materials—materials such as brain and spinal cord tissue, which have been found to concentrate the abnormal prion that causes BSE—from entering the food supply. Exposure to these materials is believed to have caused cases of new variant Creutzfeldt-Jakob disease, the human equivalent of BSE, in the United Kingdom, according to Dr. Hueston.

Additionally, the regulations limit the use of mechanical meat recovery systems.

In response to the changes, the United States has reopened its borders to low-risk ruminant products from Canada, such as boneless meat from younger animals and hunter-harvested ruminants. For more information on the status of the ban, visit www.usda.gov or read the Take Notice on page 922.

More changes expected
The international review team recommended several other changes to Canada's BSE-prevention policies that are currently under consideration. These include tighter controls on nonruminant feed to prevent exposure of ruminants, strengthened tracking and tracing systems, improved disease testing and surveillance, and efforts to improve awareness among producers, veterinarians, and the public.

"The Canadian Food Inspection Agency and Health Canada have accepted the balance of the recommended changes to BSE-related policies," said Lyle Vanclief, the Canadian Minister of Agriculture, in a statement. "We are determined to revise these policies as quickly as possible. However, many of these changes are complex and require coordination—even harmonization with the provinces, the industry, and the United States, and must reflect the integrated North American beef industry."

Some of the changes currently under consideration are removing specified risk materials from the feed chain and possibly changing animal feed regulations to exclude material from dead, dying, diseased, or disabled cattle, according to Dr. Kahn. Canada also may step up its BSE surveillance program, which has tested 10,500 animals to date.

Officials in the United States also have acknowledged the need to coordinate any changes in U.S. BSE policies.

"When you look at the amount of trade that goes both ways across the border, there probably are implications (for the United States); that's why we are trying to harmonize any actions or policy decisions with the Canadians," said Dr. Lisa Ferguson, a senior staff veterinarian at the USDA Animal and Plant Health Inspection Service.

The Food and Drug Administration may also consider changing the existing U.S. feed ban, Dr. Ferguson said.

An evolving understanding of BSE
Many of the recommendations in the international team's report reflect the growing body of scientific knowledge about BSE.

BSE is a degenerative neurologic disease that affects the central nervous system of cattle. The disease was first diagnosed in the United Kingdom in 1986, and since then, research has helped elucidate how it is spread.

The primary means of transmission is believed to be cattle eating feed contaminated by the rendered material from other BSE-infected cattle. The abnormal prion, a misfolded protein, that causes BSE is very stable and is not completely denatured by the normal rendering process.

According to Dr. Hueston, older cattle present a greater risk for spreading the disease because the prions have had sufficient time to accumulate in many tissues, whereas in cattle less than 30 months old, prions have been found to concentrate predominantly in the intestines. Because of this, many of the international team's recommendations specify different measures for dealing with the carcasses of young and older cows.

Vertebral columns from animals over 30 months old will no longer be processed by mechanical meat recovery systems in Canada.

Dr. Hueston explained that these mechanical systems do not differentiate between meat and nerve tissue, thereby potentially allowing nerve tissue—which is known to concentrate prions in older animals—into the human food supply. The mechanical systems were implemented to protect workers from the dangerous and repetitive hand-deboning work but had unexpected consequences, he said.

"It was largely driven by the best of intentions, (with meat processors) saying 'how can we protect our workers, while being most efficient in removing meat from the bones?'" Dr. Hueston said. "Inadvertently, (mechanical systems) incorporated nervous tissue in meat products, which was later found to be where BSE infectivity accumulated."

On the basis of research to date, the most important step countries can take is dealing with specified risk materials, Dr. Hueston said. "Make sure you have in place a system to deal with SRMs, to deal with their safe disposal, strengthen the surveillance system, and block every opportunity for recycling."

Lessons learned
The discovery of a BSE-infected cow put the Canadian BSE surveillance system and the Canadian Food Inspection Agency to the test.

The infected cow, an older Black Angus-type cow, had pneumonia, was unable to rise, and was condemned at slaughter in January, said Dr. Frederique Moulin, the veterinary coordinator for the Animal Products Directorate. Specimens from the animal were submitted for testing as part of the country's BSE surveillance program, but they were not given a high priority because the animal did not show neurologic signs of disease, Dr. Moulin said.

In mid-May, tests were performed at a provincial laboratory and at the CFIA's National Center for Foreign Animal Disease, and investigators tentatively diagnosed BSE. The samples were sent to the World Reference Laboratory in the United Kingdom, where BSE was verified on May 20.

The infected cow's herd was quarantined on May 18, as officials awaited confirmation. Canadian officials launched an intensive investigation immediately after confirmation was received. The investigation followed three lines of inquiry: determining the birthplace of the diseased cow and tracking her herd mates that might have received the same feed, identifying the whereabouts of her offspring, and tracing the rendered remains of the diseased cow. In the process, 18 farms were quarantined and more than 2,700 animals were depopulated and tested. No other diseased animals were discovered among the cow's offspring, herd, or other animals.

At the time of slaughter, the cow was declared unfit for human consumption and no meat from the animal directly entered the human food supply, according to documents from the CFIA.

The cow's remains were sent for rendering and may have ended up in pet food, nonruminant animal feed, and fertilizer. As part of the investigation, Canadian officials inspected the slaughterhouse and rendering plant where the cow was processed, and the feed mills, farms, and pet food producers that may have received rendered material from the diseased cow. As a precaution, Canadian and U.S. officials recalled some dried dog food products that may have contained rendered material from the diseased cow. Canadian officials also quarantined some farms that may have received rendered products or feed containing rendered products from the diseased cow, and they tested animals on those farms.

The international team applauded the comprehensive scope of the Canadian BSE investigation and the willingness of the country to share information and communicate with the public.

Dr. Ferguson said the USDA has learned a lot from the way the Canadian government has handled communication with consumers and other governments.

"They've been very open, very transparent, and they've tried to approach everything from a scientific basis. It's been very encouraging that they haven't seen the consumer confidence issues other countries have had when they find BSE," she said.

The importance of preparedness and the need to harmonize disease regulations with international standards were lessons the CFIA has learned from the investigation, according to Dr. Kahn.

"You need to mount a quick response and get people with the right skills involved very quickly," she said. "With BSE, it's not a contagious disease like foot-and-mouth disease, where you've got this race against time because the disease is spreading almost faster than you can get out and investigate it. But (in the interest of) public communication and reassuring trade partners, you've got to get out there quickly and provide information in a timely way."

Dr. Kahn also emphasized the importance of setting BSE policies that are consistent with international standards. She explained that Canada, like the United States, has policies for importing ruminants and ruminant products from countries that have had BSE that are much stricter than the policies of the Office of International Epizooties, the international organization that addresses global animal health.

 

Veterinarians are on the front lines of

As Canada deals with the aftermath of the discovery of a single case of bovine spongiform encephalopathy, there are many things that U.S. veterinarians can do to prevent the disease in cattle and educate the public about the disease, according to BSE experts.

First and foremost, bovine practitioners need to be sure they understand the disease, according to Dr. William Hueston, director of the Center for Animal Health and Food Safety at the University of Minnesota.

"To me, the Canadian investigation provides compelling evidence that there was BSE infectivity circulating in the feed supply prior to the announcement of the feed ban (in 1997)," Dr. Hueston said. "So that suggests we need to prepare for the possibility there will be additional cases of BSE in North America."

Dr. Lisa Ferguson, a senior staff veterinarian at the Department of Agriculture's Animal and Plant Health Inspection Service, said the likelihood of a widespread outbreak of BSE in the United States is "almost negligible" because of the preventive measures in place, but that veterinarians should be vigilant.

"I would encourage practitioners, especially bovine practitioners, to be very observant," Dr. Ferguson said. If they see odd signs, especially neurologic signs, she said, "They should contact us with any questions."

The signs of BSE in cattle include gradual changes in a cow's behavior, such as increased nervousness or aggression, abnormal posture, incoordination, and inability to rise.

Another critical component for controlling the disease in cattle is to prevent recycling of the BSE prions through cattle feed, Dr. Hueston said.

"We know from the Canadian investigation that the control methods for blocking recycling were largely working—they were probably 98 to 99 percent effective—but there were some exceptions," he said. "There were situations in which potentially contaminated feed or prohibited feeds were finding their way back to cattle. The bovine practitioner has an important role in educating clients to help assure 100 percent compliance with feed restrictions to break that recycling."

All veterinarians, even those who work exclusively with small animals, have a role to play in educating the public about BSE, Dr. Hueston said. "I think it's the obligation of veterinarians to share scientifically sound information. That information relates to means of spread of the disease and the route of potential exposure in humans," he said.

For more information on BSE and its public health implications, visit the following Web sites:

USDACDCCanadian Food Inspection AgencyAcademic Health Center - University of Minnesota