Mad cows, cannibalism, cow offal in sausage and Oprah in Amarillo all loomed large in the School of Public Health's February Dean's Lecture by Richard Johnson, professor of neurology and molecular microbiology and Immunology. Johnson said mad cow disease, or bovine spongioform encephalopathy, has become the "soap opera of medicine."
In spite of the downpour outside, a standing-room-only crowd packed a second-floor auditorium on Feb. 4 to hear whether Johnson, a neuroscientist and virologist, believed mad cow disease was headed this way, or if it had perhaps already arrived.
The "soap opera," Johnson said, began in April 1985, when a British dairyman noticed one of his cows wobbling and acting aggressively. That cow and several others exhibiting bizarre behavior were killed and found to have BSE. Apparently, the cows had contracted the disease from feed made from animal carcasses. Three years later, when 2,184 cows with BSE were identified, the United Kingdom banned the use of cattle carcasses in ruminant feed.
But the chain had another link: Ground-up cattle offal was used as binder in hamburger and sausage, and it was not until 1989, when 7,137 cows were diagnosed with BSE, that the British government prohibited the use of ground-up cow parts in human food.
The BSE epidemic may have been touched off by a crisis in the tallow industry. Livestock carcasses, as well as animals killed by cars and in animal shelters, are made into tallow, lard and bone meal. In the late 1970s, when people turned from lard to vegetable oils for cooking, the British rendering industry was forced to put more of the tallow into bone meal products. This extra fat is now thought to have protected and extended the life of prions, the mysterious proteins that cause BSE, which were then passed on to cattle in their feed.
The human disease resembling BSE, Creutzfeld-Jakob disease, is found world-wide but is extremely rare, Johnson said, noting there is about one case per million a year. Although there have been no widespread outbreaks of the disease, there is widespread fear. Johnson recalled that in 1996 a colleague in Britain declared that "mad cow disease could not spread to humans, essentially because a prior parliamentary commission said it couldn't." At the other end of the spectrum were those who declared it the "AIDS of the 21st century."
Johnson said there is no occupational risk factor, and there have been no instances of spouses catching CJD from one another. Yet through organ transplants, contaminated neurosurgical instruments and hormones derived from human pituitaries, the disease has been transmitted among humans. And, "the evidence strongly supports the idea that BSE has been transmitted to humans," Johnson said.
There have been no cases of CJD related to BSE found in the United States, but there are concerns, Johnson said. First, prior to 1989, British cattle were imported to this country, and some could have entered the food chain. Second, it is unclear how prions are generated in animal brains; it may be possible for BSE to appear spontaneously. Last, researchers in northeast Colorado and southeast Wyoming recently found that 5 percent of the deer killed by hunters had a form of spongiform encephalitis, and some of the hundreds of thousands of road-killed deer collected each year are processed by rendering plants.
"Do I eat beef?" Johnson asked rhetorically. "Yes. Did I eat it
in Britain? Yes. Human disease related to BSE will not be the
AIDS of the 21st century. We probably will see 10, 40 or 100 more
cases, but new regulations in England have stopped the outbreak
in cattle, and human cases should be limited."