By Lindsay Toler
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By Allison Babka
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In an effort to guard against spreading the disease, the U.S. Food and Drug Administration issued a feed ban in 1997, prohibiting the then-widespread practice of feeding ruminant tissue back to other ruminants. A previous crucial step had been the 1989 import ban, which followed discovery of the disease in Britain and Europe and restricted imports from countries with known BSE cases. In response to the European outbreak, Britain now tests all slaughtered cattle over 24 months of age; France and Germany test more than half of all cattle slaughtered. Not to be outdone, the Japanese now test each and every slaughtered animal.
The United States, meanwhile, has traditionally tested only 20,000 of the roughly 35 million cattle slaughtered annually. And while scientists now believe BSE is able to survive its passage through the food chain, the FDA ban did not prohibit the common practice of weaning calves on cattle blood. The ban also continued to allow plate waste -- leftovers from institutions like prisons and universities -- to be fed to cattle and permitted bovine tissue to be fed to chickens (which may later be fed back to cattle in the form of chicken-farm byproducts containing dung, food, feathers and urine).
The FDA announced in January that it was working to close these loopholes, but to date the agency has published no final rule. Regardless, some fear the interim period has provided ample opportunity for BSE to slip undetected into the cattle supply. "You still have the problem of all the time prior to the exceptions ban," points out Peter Lurie, deputy director of health research for Public Citizen, a consumer-advocacy group. "The two most important things are the feed ban and the import ban. The feed ban is important because what sustains an epidemic is the feeding of cattle to cattle. If a human being eats an infected piece of meat, they may become ill and die, and that would be tragic. But the infection ends with them. What makes it worse is if the cattle eat the cattle: Then many, many more humans would have the opportunity to eat infected meat."
While the burden of regulating livestock feed falls on the administrative shoulders of the FDA, it is the USDA that is responsible for regulating beef production. In an effort to further insulate the beef supply from the disease, that agency announced early this year that it was expanding the list of cattle and cattle parts that are prohibited from entering the human food supply. Under the new rules, all "downer cattle" -- animals that are rendered unable to walk owing to broken limbs or neurological disorders (or premature death) -- are banned from the human food supply. The skull, brain, eyes, vertebral column and spinal cord -- the so-called specified risk materials -- of cattle over 30 months old are likewise off-limits, as is the small intestine, regardless of the animal's age.
"Whatever infection level there might be in blood [transmitted to calves weaned on cattle blood] -- and there probably is some -- it pales in comparison to the infection levels in the central nervous system, and so that's where the guts of the thing needs to be," Lurie argues. "The exceptions [to the feed ban] are important, and they need to be done away with, but the most important thing is the enforcement of the guts of the [original] ban."
It is in the guts, literally, that scientists are able to first detect BSE. According to the latest research, the protein can be isolated in an animal's small intestine six months after infection. The trouble is, detection entails a labor-intensive process that requires an entire year; after it is harvested, the protein must then be injected into mice to confirm its identity. Moreover, in order to retrieve the protein in the first place, the calf has to be killed. "The next time you can find the agent is about two years later in the brain and spinal cord," says Dr. William Hueston, a veterinarian who led the USDA's first BSE risk assessment in 1990. "So there's this very long lag time."
To further obscure matters, an infected animal will often appear perfectly normal. It's not until about 30 months after exposure that the animal will begin to show outward signs of infection, when the disease begins to destroy the brain. "It's an incredible disease," marvels Hueston, who served as the USDA's BSE spokesman before joining the faculty at the University of Minnesota. The only practical tests currently available are very limited in their effectiveness, Hueston adds. "The diagnostic tests we have can only detect the disease within three to six months prior to the animal showing any abnormal behavior," he explains. "So all of the rest of the life of the animal -- even though it's exposed -- it's perfectly normal by all the tests we currently have."
In other words, even if every single animal in the nation were to be tested under current practical methods, infected cattle could easily slip through undetected. Nonetheless, the disease has been found to occur in animals less than 30 months of age, and no less a luminary than Nobel laureate Stanley Prusiner now believes BSE can occur spontaneously.