Mad Cow Case May Predate Feed Ban
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By Shankar Vedantam
Washington Post Staff Writer
Tuesday, December 30, 2003; Page A01
washingtonpost.com
A U.S. Holstein probably was infected with mad cow disease before safety bans were enacted in 1997 on feed in the United States and Canada, officials said yesterday.
The infection probably occurred around the same time as a beef cow from the Canadian province of Alberta became sick. Scientists may need to increase monitoring of thousands of cattle born before the bans were enacted on potentially infected feed, through which the disease spreads. The animals are now spread across the continent.
"The age of the animal is especially important because it is a likely explanation" for the Holstein's infection, said W. Ron DeHaven, deputy administrator and chief veterinary officer at the U.S. Department of Agriculture. "She was born before feed bans were implemented in North America."
U.S. officials are trying to trace the Washington state Holstein to an Alberta farm using DNA tests. But Canada's top veterinarian said that even if such a link is shown, there seems to be no one source of contaminated feed that could have gone to both the Holstein and the beef cow found infected in May.
The two infected animals did not come from the same farm, no animal exchanges took place between the farms, and feed records do not indicate a common source of contamination, Brian Evans, Canada's chief veterinarian, said yesterday. That makes it all the harder for scientists to trace the tainted feed and determine how widespread its use was.
"We are going to go back another step in the chain to the feed mills to find out where they purchased the raw materials -- are they from a common source?" Evans said in an interview.
Every step further back that investigators go to track the source of the infection exponentially increases the risk that other animals born before the feed bans might have eaten the same contaminated feed, and that the disease has spread more widely than is now known.
Evans said officials in both countries will be forced to take a closer look at thousands of cattle in the 6-to-8-year-old range, which were born before the feed bans. New surveillance measures will be necessary, he said. DeHaven also indicated that U.S. surveillance probably will be strengthened.
Wherever the infection may have started, it is now a cross-border problem: U.S. and Canadian authorities have repeatedly emphasized that the beef and dairy industries in both countries are tightly integrated. "Tens of hundreds of thousands of animals have crossed that border on an annual basis over many, many years," Evans said. "If we are going to manage this, it has to be managed on both sides."
The feed bans keep potentially infected feed from being given to cattle. The bans went into effect in August 1997 in the United States and Canada, after an outbreak of mad cow disease in Britain. Most scientists believe the risk for infection is highest among newborn cattle. The beef and dairy industries remove calves from their mothers shortly after birth -- the milk is more valuable in grocery stores than in the calves -- so the young animals need an alternate source of protein. For years, the industry gave calves feed that included brain and spinal tissue from slaughtered cows.
Bovine spongiform encephalopathy, or mad cow disease, is transmitted through such feed, which may contain misshapen proteins known as prions. The disease is associated with a fatal brain-wasting human disorder called variant Creutzfeld-Jakob disease. The illness has killed 154 people, mostly in Britain. There is no cure, and infected people usually show no symptoms for years.
On Saturday, U.S. officials said that based on an ear tag match, the infected Holstein was brought over the border in August 2001. But the Holstein that came over the border at Eastport, Idaho, was born in April 1997, according to Canadian records. Documents at the Washington state farm, identified as the Sunny Dene Ranch in Mabton, indicated the animal was born around 1999, U.S. officials had said after the case came to light Dec. 23.
Yesterday, U.S. officials said new records found at the Washington farm placed the age of the Holstein close to the age in the Canadian documents -- increasing the likelihood that they were the same animal -- and implicating a source of contaminated feed before the safety bans took effect. New records were unearthed by the owner of the Mabton farm after "an extensive search of his records," DeHaven said.
Because there is still some discrepancy between the U.S. and Canadian farm records, officials on both sides agree that a DNA test will be the only conclusive proof that they are talking about the same animal. Samples from the Holstein's brain, which were used in the test for mad cow disease, will be compared with DNA from its father. The bull, Canadian records show, was a Holstein that was widely used in artificial insemination programs.
Tests will be conducted separately in Canada and the United States over the next few days, and a third sample will be held as a control in case the test results do not match. Investigators are also exploring the possibility of comparing DNA from two living calves that the Holstein had at the Mabton farm with a calf that Canadian records show was born there -- assuming that investigators in both countries can identify the specific animals.
"One of her offspring in Canada may still be alive, either in Canada or the United States," Evans said in the interview.
Two of the Holstein's calves that were born in Mabton are in herds in Washington state that have been placed under quarantine.
Investigators also said yesterday that more animals born before the feed ban may have come over from Canada with the infected Holstein than previously believed. Although the importation records initially indicated 74 animals came over the border in a herd that included the infected Holstein, new documents indicate eight more animals soon followed from the same Alberta farm, DeHaven said.
Investigators are trying to track down all 81 animals that might have eaten the same contaminated feed as the Holstein before the feed ban went into effect. On Saturday, DeHaven said he believed that most of the animals were still alive. Experts believe a minority of cattle that eat infected feed will become sick but say it is difficult to quantify the risk for an individual animal.
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