Mad Cow Disease

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Mad cow disease

Mad cow disease, a relatively newly discovered malady, was first identified in Britain in 1986, when farmers noticed that their cows' behavior had changed. The cows began to shake and fall, became unable to walk or even stand, and eventually died or had to be killed. It was later determined that a variation of this fatal neurological disease, formally known as Bovine Spongiform Encephalopathy (BSE), could be passed on to humans.

It is still not known to what extent the population of Britain and perhaps other countries is at risk from consumption of contaminated meat and animal by-products. The significance of the BSE problem lies in its as yet unquantifiable potential to not only damage Britain's $7.5 billion beef industry, but also to endanger millions of people with the threat of a fatal brain disease.

A factor that stood out in the autopsies of infected animals was the presence of holes and lesions in the brains, which were described as resembling a sponge or Swiss cheese. This was the first clue that BSE was a subtype of untreatable, fatal brain diseases called transmissible spongiform encephalopathies (TSEs). These include a very rare human malady known as Creutzfeldt-Jakob Disease (CJD), which normally strikes just one person in a million, usually elderly or middle-aged. In contrast to previous cases of CJD, the new bovine-related CJD in humans is reported to affect younger people, and manifests with unusual psychiatric and sensory abnormalities that differentiate it from the endemic CJD. The BSE-related CJD has a delayed onset that includes shaky limb movements, sudden muscle spasms, and dementia.

As the epidemic of BSE progressed, the number of British cows diagnosed began doubling almost yearly, growing from some 7,000 cases in 1989, to 14,000 in 1990, to over 25,000 in 1991. The incidence of CJD in Britain was simultaneously increasing, almost doubling between 1990 and 1994 and reaching 55 cases by 1994. In response to the problem and growing public concern, the government's main strategy was to issue reassurances. However, it did undertake two significant measures to try to safeguard public health. In July 1988, it ostensibly banned meat and bone meal from cow feed, but failed to strictly enforce the action. In November 1989, a law that intended to remove those bovine body parts considered to be the most highly infective (brain, spinal cord, spleen, tonsils, intestines, and thymus) from the public food supply was passed. A 1995 government report revealed that half of the time, the law was not being adhered to by slaughterhouses. Thus, livestock—and the public—continued to be potentially exposed to BSE.

As the disease continued to spread, so did public fears that it might be transmissible to humans, and could represent a serious threat to human health. But the British government, particularly the Ministry of Agriculture, Fisheries, and Food (MAFF), anxious to protect the multibillion dollar cattle industry, insisted that there was no danger to humans. However, on March 20, 1996, in an embarrassing reversal, the government officially admitted that there could be a link between BSE and the unusual incidence of CJD among young people. At the time, 15 people had been newly diagnosed with CJD. Shocking the nation and making headlines around the world, the Minister of Health Stephen Dorrell announced to the House of Commons that consumption of contaminated beef was "the most likely explanation" for the outbreak of a new variant CJD in 10 people under the age of 42, including several teenagers. Four dairy farmers, including some with infected herds, had also contracted CJD, as had a Frenchman who died in January 1996.

British authorities estimated that some 163,000 British cows had contracted BSE. But other researchers, using the same database, put the figure at over 900,000, with 729,000 of them having been consumed by humans. In addition, an unknown number had been exported to Europe, traditionally a large market for British cattle and beef. Many non-meat products may also have been contaminated. Gelatin, made from ligaments, bones, skin, and hooves, is found in ice cream, lipstick, candy, and mayonnaise; keratin, made from hooves, horns, nails, and hair, is contained in shampoo; fat and tallow are used in candles, cosmetics, deodorants, soap, margarine, detergent, lubricants, and pesticides; and protein meal is made into medical and pharmaceutical products, fertilizer , and food additives . Bone meal from dead cows is used as fertilizer on roses and other plants, and is handled and often inhaled by gardeners.

In reaction to the government announcement, sales of beef dropped by 70%, cattle markets were deserted, and even hamburger chains stopped serving British beef. Prime Minister Major called the temporary reaction "hysteria" and blamed the press and opposition politicians for fanning it.

On March 25, 1996, the European Union banned the import of British beef, which had since 1990 been excluded from the United States and 14 other countries. Shortly afterwards, in an attempt to have the European ban lifted, Britain announced that it would slaughter all of its 1.2 million cows over the age of 30 months (an age before which cows do not show symptoms of BSE), and began the arduous task of killing and incinerating 22,000 cows a week. The government later agreed to slaughter an additional l00,000 cows considered most at risk from BSE.

A prime suspect in causing BSE is a by-product derived from the rendering process, in which the unusable parts of slaughtered animals are boiled down or "cooked" at high temperatures to make animal feed and other products. One such product, called meat and bone meal (MBM), is made from the ground-up, cooked remains of slaughtered livestock—cows, sheep, chicken, and hogs—and made into nuggets of animal feed. Some of the cows and sheep used in this process were infected with fatal brain disease. (Although MBM was ostensibly banned as cattle feed in 1988, spinal cords continued to be used.)

It is theorized that sheep could have played a major role in initially infecting cows with BSE. For over 200 years, British sheep have been contracting scrapie, another TSE that results in progressive degeneration of the brain. Scrapie causes the sheep to tremble and itch, and to "scrape" or rub up against fences, walls, and trees to relieve the sensation. The disease, first diagnosed in British sheep in 1732, may have recently jumped the species barrier when cows ate animal feed that contained brain and spinal cord tissue from diseased sheep. In 1999 the World Health Organization (WHO) implored high-risk countries to assess outbreaks of BSE-like manifestations in sheep and goat stocks. In August 2002, sheep farms in the United Kingdom demonstrated to the WHO that no increase in illnesses potentially linked to BSE occurred in non-cattle livestock. However, that same year, the European Union Scientific Steering Committee (SSC) on the risk of BSE identified the United Kingdom and Portugal as hotspots for BSE infection of domestic cattle relative to other European nations.

Scrapie and perhaps these other spongiform brain diseases are believed to be caused not by a virus (as originally thought) but rather by a form of infectious protein-like particles called prions, which are extremely tenacious, surviving long periods of high intensity cooking and heating. They are, in effect, a new form of contagion. The first real insights into the origins of these diseases were gathered in the 1950s by Dr. D. Carleton Gajdusek, who was awarded the 1976 Nobel Prize in Medicine for his work. His research on the fatal degenerative disease "kuru" among the cannibals of Papua, New Guinea, which resulted in the now-familiar brain lesions and cavities, revealed that the malady was caused by consuming or handling the brains of relatives who had just died.

In the United States, Department of Agriculture officials say that the risk of BSE and other related diseases is believed to be small, but cannot be ruled out. No BSE has been detected in the United States, and no cattle or processed beef is known to have been imported from Britain since 1989. However, several hundred mink in Idaho and Wisconsin have died from an ailment similar to BSE, and many of them ate meat from diseased "downer" cows, those that fall and cannot get up. Some experts believe that BSE can occur spontaneously, without apparent exposure to the disease, in one or two cows out of a million every year. This would amount to an estimated 150–250 cases annually among the United States cow population of some 150 million. Moreover, American feed processors render the carcasses of some 100,000 downer cows every year, thus utilizing for animal feed cows that are possibly seriously and neurologically diseased.

In June 1997, the Food and Drug Administration (FDA) announced a partial ban on using in cattle feed remains from dead sheep, cattle, and other animals that chew their cud. But the ruling exempts from the ban some animal protein, as well as feed for poultry, pigs, and pets. In March of that year, a coalition of consumer groups, veterinarians, and federal meat inspectors had urged the FDA to include pork in the animal feed ban, citing evidence that pigs can develop a form of TSE, and that some may already have done so. The coalition had recommended that the United States adopt a ban similar to Britain's, where protein from all mammals is excluded from animal feed, and some criticized the FDA's action as "totally inadequate in protecting consumers and public health."

The United States Centers for Disease Control (CDC) has reclassified CJD that is associated with the interspecies transmission of BSE disease-causing factor. The current categorization of CJD is termed new variant CJD (nvCJD) to distinguish it from the extremely rare form of CJD that is not associated with BSE contagion. According to the CDC, there have been 79 nvCJD deaths reported worldwide. By April 2002, the global incidence of nvCJD increased to 125 documented reports. Of these, most (117) were from the United Kingdom. Other countries reporting nvCJD included France, Ireland, and Italy. The CDC stresses that nvCJD should not be confused with the endemic form of CJD. In the United States, CJD seldom occurs in adults under 30 years old, having a median age of death of 68 years. In contrast, nvCJD, associated with BSE, tends to affect a much younger segment of society. In the United Kingdom, the median age of death from nvCJD is 28 years. As of April 2002, no cases of nvCJD have been reported in the United States, and all known worldwide cases of nvCJD have been associated with countries where BSE is known to exist. The first possible infection of a U.S. resident was documented and reported by the CDC in 2002. A 22-year-old citizen of the United Kingdom living in Florida was preliminarily diagnosed with nvCJD during a visit abroad. Unfortunately, the only way to verify a diagnosis with nvCJD is via brain biopsy or autopsy. If confirmed, the CDC and Florida Department of Health claim that this case would be the first reported in the United States.

The outlook for BSE is uncertain. Since tens of millions of people in Britain may have been exposed to the infectious agent that causes BSE, plus an unknown number in other countries, some observers fear that a latent epidemic of serious proportions could be in the offing. (There is also concern that some of the four million Americans alone now diagnosed with Alzheimer's disease may actually be suffering from CJD.) There are others who feel that a general removal of most infected cows and animal brain tissue from the food supply has prevented a human health disaster. But since the incubation period for CJD is thought to be 7–40 years, it will be some time before it is known how many people are already infected and the extent of the problem becomes apparent.

[Lewis G. Regenstein ]