Peter Montague
In 1985, cows in Britain began to die of a mysterious ailment that no-one had ever seen before. The cows staggered and drooled, their ears twitching. Then they began to show signs of fear, grinding their teeth, acting aggressively toward other animals. Soon they died. Farmers named the condition "mad cow disease", and the name stuck.
The disease is now known formally as "bovine spongiform encephalopathy". BSE is one of a small family of diseases called transmissible spongiform encephalopathies, or TSEs. TSEs destroy neurons, the main nerve cells in the brain, creating holes that leave the brain resembling a sponge. BSE, like the other TSEs, is infectious.
During the 13 years since it first appeared, mad cow disease has killed more than 167,000 cows in Britain, and many more became infected but were slaughtered for food before symptoms appeared. Symptoms take an average of five years to show up after a cow is infected.
British-type BSE has now been observed in cows in Switzerland, the Netherlands, Ireland, Portugal, France, Oman and the Falkland Islands. To date, it has not been observed in the US.
When the disease first struck in Britain, health authorities insisted that British beef was safe to eat. For 10 years they defended that position aggressively, despite mounting evidence to the contrary.
Then in 1996, a panel of government scientists told parliament that the "most likely explanation" for 10 cases of a new TSE disease in humans was that BSE had moved from cows into people. That explanation is now widely accepted by most scientists, though airtight evidence remains elusive.
By 1996, some British experts calculated, more than a million infected cows had already been consumed in Britain.
In humans, the BSE-like disease is called "new variant Creutzfeld-Jakob disease", or nvCJD. Creutzfeld-Jakob disease (CJD) is a member of the TSE family. CJD has been recognised for a long time as a rare disease of the elderly, but nvCJD strikes young people, even teenagers. Between 1995 and early 1998, at least 23 people died of nvCJD in Britain and at least one in France, the oldest of them aged 42 and the youngest 15.
In January 1997, British epidemiologists tried to estimate how large the outbreak of nvCJD might become. They concluded that the data were not sufficient to allow a precise estimate, because no-one knows for sure how much time elapses between infection and the appearance of symptoms.
In a nutshell, mad cow disease developed because of a little-known but very widespread modern agricultural practice — feeding dead cows to cows, thus turning a vegetarian species into meat-eaters.
In Britain and the US, when a cow is slaughtered, about half of the animal cannot be sold for human uses — the hide, bones, entrails, hooves, horns, fat, gristle and tough membranes are, by law, not permitted to be used in food. Something else has to be done with these parts.
Then there are "downer cows". Cows that cannot stand up, cows that collapse and cows that die mysteriously are called "downers." Every year in the US about 100,000 cows die of unknown causes. Something must be done with their carcasses.
In addition, thousands of pigs, horses, chickens and sheep die of unknown causes each year. To prevent public health problems, they must be disposed of. Then there is road kill — deer, elk and other large mammals killed by motor vehicles.
In the US all of these animals and animal parts end up at 280 "rendering" plants, where they are ground up and boiled down. Until the 1960s, the fat from rendering plants was generally used to make soap.
The invention of detergents greatly reduced the demand for soap. As a result, the rendering industry had to develop new markets. It hit on animal feed, which became a great commercial success.
From the 1960s, rendering plants dried their rendered products, ground them into the consistency of brown sugar and sold them for animal feed. Feed mills then mixed these animal by-products into various feed formulations — about one-third for cattle, one-third for pigs and chickens, and one-third for pets.
Some of the animals sent to rendering plants are sheep killed by a disease called "scrapie". Scrapie is another TSE, which takes its name from the way sheep act once they get the disease — they rub up against a fence or a barn until they scrape away their wool, leaving raw wounds. Then they die.
Scrapie has been a well-known, though mysterious, disease of sheep for at least 200 years, but only recently have scrapie-infected sheep been fed to cows. Scientists who study mad cow disease believe that the illness crossed the species barrier from sheep to cows through contaminated feed. Indeed, the British in 1988 banned the feeding of animal carcasses to other animals, and within seven years new cases of mad cow disease diminished from 900 to 1000 per week to 280 to 300 per week.
The US has been slow to act. From October 1988 to June 1989, scrapie was diagnosed in 52 flocks of sheep in 20 US states. Clearly, there was ample reason to ban the feeding of animal carcasses to animals in the US when the British took that action in 1988. However, the beef industry, and the rendering and feed industries, have generally opposed such precautionary measures.
TSEs have a very long incubation period. In cows, BSE takes three to eight years from the time of first infection to the appearance of symptoms shortly before death. Thus, by the time symptoms of BSE appear, many cows are likely to be carrying the infection silently.
This was confirmed earlier this year in Switzerland, when tests of brain tissues from 1761 cows revealed eight infected animals without any symptoms, for a "silent" infection rate of 4.5 per 1000. This is 100 times as high as the rate of Swiss cows showing symptoms.
If this rate holds for Britain, it means that today there are about 460,000 British cows infected but symptom-free in a total herd of roughly 11 million.
Furthermore, the infectious agent is incredibly resistant to deactivation. Cooking infected meat, or even rendering it at high temperature, does not completely eliminate its infectivity. Animals get TSEs by eating infected animals or parts of infected animals, especially nerve tissues.
TSE diseases have now been identified in sheep, pigs, goats, cattle, deer, elk, mink, mice, hamsters, guinea pigs, domestic cats, puma, cheetah, eland, kudu, Arabian oryx, myland, marmosets, macaques, chimpanzees and humans. In addition, a TSE has been reported in ostriches in a German zoo.
Thus one might think the US Food and Drug Administration (FDA) would prohibit the feeding of any animals to any other animals, as the British did in 1988, but that is not what the FDA has done. Under pressure from the beef, rendering and feed industries, in 1997 FDA prohibited only the feeding of ruminants and mink to ruminants. Mink are included because they can get a TSE similar to mad cow disease.
FDA still allows the feeding of pigs to other animals, and the feeding of blood and gelatin from rendering plants to all animals. Many calves in the US are being raised on a diet of dried blood taken straight from rendering plants. Pigs and chickens are still being fed rendered animal products. There are sound scientific arguments why this policy represents a form of Russian roulette being played with the health of the public.