Feb 4, 2004 (CIDRAP News) A panel of experts that reviewed the US response to the nation's first case of bovine spongiform encephalopathy (BSE) says there are probably other cases in the United States and recommends increasing restrictions designed to keep BSE-infected materials out of human food and animal feed.
The panel's report, released today, recommends that high-risk cattle tissues be banned from food for humans and animals, including pets. The panel defined these high-risk tissues, called specified-risk materials (SRM), as the brain, spinal cord, skull, and vertebral column of cattle older than 1 year, plus the intestines of all cattle.
Current rules ban the use of SRMs from cattle more than 30 months old (and the small intestine of all cattle) in human food but allow them in pet food and feed for nonruminant animals, such as poultry and pigs. But the panel said that in commercial plants that make feed for cattle and nonruminant animals, cattle parts can accidentally end up in cattle feedthe problem referred to as cross-contamination.
Current rules also prohibit the use of cattle parts and protein from most other mammals in cattle feed. The panel recommends broadening this restriction to include all mammalian protein and poultry protein as well. This would help prevent cross-contamination and also prevent cattle protein in the intestines of slaughtered pigs or poultry from ending up in cattle feed, the report says.
Cattle contract BSE by eating feed containing infectious material from other cattle. Eating meat products from infected cattle is believed to be the cause of variant Creutzfeldt-Jakob disease (vCJD), a fatal human disease similar to BSE.
The five-member international committee presented its report today at a meeting of the US Department of Agriculture's (USDA's) Advisory Committee on Foreign Animal and Poultry Diseases. The group included Ulrich Kihm, former chief veterinary officer of Switzerland; Will Hueston, director of the University of Minnesota Center for Animal Health and Food Safety; D. Matthews of the United Kingdom; Stuart C. McDiarmid of New Zealand, and Dagmar Heim, chief of BSE control in Switzerland. Kihm, Hueston, McDiarmid, and Heim made up a panel that reviewed Canada's BSE response in 2003.
The panel said the BSE-infected cow that was discovered in Washington state in December may be the only infected cow from its original Canadian herd. "However, it is probable that other infected animals have been imported from Canada and possibly also from Europe," the report says. "These animals have not been detected and therefore infective material has likely been rendered, fed to cattle, and amplified within the cattle population, so that cattle within the USA have also been indigenously infected."
For the past several weeks, the USDA has been tracing cattle that came from the same Alberta birth herd as the BSE-infected cow. But because there may be no other infected cows from the Canadian herd and because the nation probably has other unrelated BSE cases, the USDA should stop trying to trace those cows and focus instead on broader BSE- prevention efforts, the panel says.
"Under the circumstances, the subcommittee believes that the epidemiological investigation should cease, and resources be redirected into the planning, implementation, and enforcement of an extended, targeted, surveillance programme and other measures to protect human and animal health," the report states.
In discussing SRM, the panel says the USDA's current ban on SRM from cattle over 30 months old (and the small intestine of all cattle) from the human food supply meets World Organization for Animal Health (OIE) standards, given the number of BSE cases seen so far. But, in view of the evidence that the BSE agent was already present before the 1997 ban on feeding cattle parts back to cattle, "strong consideration should be given to excluding all SRM from both the human and animal feed supplies."
The 30-month age threshold used in the current SRM ban was chosen because it represents about half of the average 60-month incubation period for BSE, according to the report. Changing the threshold to 12 months is warranted because "some cattle under 30 months of age may be slaughtered with infectivity present" in the SRM.
Concerning feed restrictions, the report says evidence from Europe indicates that the current ban on the use of cattle parts in cattle feed is "insufficient to prevent exposure of cattle to the BSE agent." Early in Europe's BSE outbreak, similar restrictions allowed BSE to continue to spread, though less than it would have without the restrictions.
Studies in the United Kingdom showed cattle were at risk for infection by eating feed that had been accidentally contaminated with cattle material during manufacture, the panel reports. Researchers found that cattle could be infected by ingesting as little as 10 mg of infectious brain tissue. Preventing this level of cross-contamination is nearly impossible in mills that make cattle feed and also make pig and poultry feed containing cattle material, the panel concluded.
In other conclusions, the panel does not endorse testing of all cattle for BSE, as Japan is doing. The group "considers testing of all cattle slaughtered for human consmption to be unjustified" for protecting human and animal health. The USDA's BSE testing program focuses mainly on "downer" cattle, which can no longer be used in food. The report says the USDA should "strongly consider" testing a random sample of healthy slaughter cattle over 30 months old.
The panel also says that increased SRM and feed restrictions will generate a major disposal problem. Because of this, "radical and innovative solutions" for dealing with the materials, such as converting them to fuel, are needed.
While generally approving of the USDA's investigation of the BSE case, the panel questions the agency's action in euthanizing 448 claves that were reared with the bull calf that was born to the infected cow. That decision "cannot be justified on animal or public health grounds, but the decision to do so on practical and economic grounds is recognized," the report says.