Bovine spongiform encephalopathy

• 1. Introduction

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  Bovine spongiform encephalopathy, known to most people as mad cow disease, was first confirmed in a sick animal in the United Kingdom in 1986. Laboratory tests the following year pointed to the presence of the disease. By November 1987 the British Ministry of Agriculture accepted that it had a new disease on its hands. In cattle the illness is incurable and always fatal. What began as a single sick animal grew into an outbreak that touched human health, medicine, courtrooms and the beef trade on several continents. How can a misfolded protein behave like an infection? Why did the way cattle were fed carry it so far? Why is it so hard to find in a living animal? And what did it cost the people who ate beef, and the countries that sold it?

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• 2. A Rogue Protein

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  Kuru in humans, scrapie in sheep and chronic wasting disease in deer all belong to the same family as BSE. These illnesses are called transmissible spongiform encephalopathies, and each one mainly attacks the central nervous system. In cattle the culprit is a misfolded form of a normal brain protein called prion protein.

  In its healthy shape, the protein has a spiral, alpha-helical structure. In the diseased shape, that structure is converted into a flat beta sheet. The misfolded version then pushes normally folded neighbours to copy its shape, and the effect spreads in an exponential cascade. The flattened proteins link into small chains that clump together and kill cells. Mass cell death leaves lesions in the brain, which erode the animal's physical and mental abilities until it dies. Ordinary cooking and heat treatment under normal pressures do not destroy this protein. The scientific consensus is that even beef cooked well done may remain infectious.

  How the disease travels before it reaches the brain is still poorly understood. Early experiments found heavy deposits of the abnormal protein, called PrPSc, in the ileal Peyer's patches of the small intestine. Infectivity there appeared as early as four months after inoculation. By six months, the ileum was the only tissue showing infectivity, which led researchers to believe the agent replicates there.

  There is a catch. Laboratory studies use high doses, while natural infections probably involve low ones, and no infectivity has been reported in the Peyer's patches of naturally confirmed cases. Most of the abnormal protein in those patches sat inside cells called tangible body macrophages, with a smaller share in follicular dendritic cells.

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• 3. Signs And Tests

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  The World Health Organization suggested in 2002 that a cow may carry the disease for roughly four to five years before showing symptoms, although the information on timing conflicts. During that long silence, nothing looks wrong.

  When signs do appear, they can include an unsteady gait, tremors and an exaggerated reaction to certain stimuli. Hindlimb ataxia, a loss of muscle control, leaves the animal with poor balance and coordination. Behaviour changes can include aggression, nervousness, anxiety in particular situations and frenzy. Rarer signs include persistent pacing, rubbing and licking. Other signs are less specific, such as weight loss, lower milk production, lameness, ear infections and teeth grinding from pain. Once symptoms begin, they usually worsen over weeks and months. The animal becomes a downer, unable to stand, and then slips into a coma and dies.

  Finding the disease before that point has proved stubbornly difficult. The abnormal protein exists at very low levels in blood and urine, and no fully accepted method can measure it there. The traditional method examines the medulla oblongata of the brain after death, and immunohistochemistry can show where the prion protein has built up.

  In 1989, the British microbiologist Harash Narang developed a controversial test. He described the infectious agent as a nemavirus, made of single-stranded DNA fibrils with a protein coat. That view lost out to the prion theory. His touch impression technique used electron microscopy to examine impressions of brain surface, aimed at catching BSE in abattoir meat.

  A team from New York reported in 2010 that it could detect the abnormal protein even when it made up only one part in a hundred billion of brain tissue. The method combined amplification with a new technology called surround optical fiber immunoassay and antibodies specific to the protein. The team also tested blood from apparently healthy sheep that later developed scrapie, and the protein showed up long before any signs. With more development, this approach could become a blood or urine screening test for BSE.

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• 4. The Feed Trail

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  Before about 1987, meat and bone meal was a widespread protein supplement in cattle feed across Europe. It was made from the ground and cooked leftovers of slaughter, including the carcasses of sick and injured animals. Soybeans do not grow well in Europe, so farmers there turned to cheaper animal by-products instead. In the United Kingdom, the outbreak spread because the meal was fed to the young calves of dairy cows. Cattle are believed to have caught the disease from meal containing the remains of cattle that developed it spontaneously, or from scrapie-infected sheep products.

  The official British inquiry, published in 2000, concluded that the outbreak probably arose from a single point source in the southwest of England in the 1970s. It took the view that scrapie, the original suspect, was not the cause. The trigger was instead some event in the 1970s that could not be identified. The inquiry also rejected the idea that changes in processing were to blame. It said that changes in process could not have been solely responsible for the emergence of BSE, and that changes in regulation were not a factor at all.

  Alan Colchester, a neurology professor at the University of Kent, and Nancy Colchester offered a different theory in The Lancet on the 3rd of September 2005. They proposed that the most likely origin was bone meal imported from the Indian Subcontinent that contained the remains of people infected with CJD. India's government replied that the claim was "misleading, highly mischievous; a figment of imagination; absurd", and said the country had never had a case of BSE or vCJD. In The Lancet on the 22nd of January 2006, the authors answered that their theory was unprovable only in the way every other origin theory is.

  Other hypotheses reach back much further. One holds that BSE arose from a rare spontaneous form of the disease that has appeared in cattle for many centuries. Hippocrates described a similar illness in cattle and sheep in the fifth century BC. Publius Flavius Vegetius Renatus recorded cases of a comparable disease in the fourth and fifth centuries AD.

  The United States never relied on animal by-product feeds the way Europe did. Soybean meal was cheap, cottonseed meal was cheaper still, and animal products usually cost more. A 1997 rule barred feeding mammalian by-products to ruminants such as cattle and goats. Ruminant by-products could still legally go to pets, pigs and poultry, and some authors have suggested this leaves room for cases to rise.

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• 5. The Human Toll

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  A total of 233 cases of variant Creutzfeldt-Jakob disease, or vCJD, had been reported worldwide by the time of the source figures. This is the human illness believed to follow exposure to BSE. In the years after the outbreak, 177 people contracted a disease with similar neurological symptoms and died. It is a separate illness from classical Creutzfeldt-Jakob disease, which has been known since the early 1900s and is not related to BSE.

  The agent passes to people through contaminated food. Any tissue can carry it, but the greatest risk comes from the brain, spinal cord and digestive tract. For many patients there is direct evidence that they ate tainted beef. Cases also seem to track slaughtering practices that mixed nervous system tissue into mince and other beef. An estimated 400,000 infected cattle entered the human food chain in the 1980s.

  Three cases occurred in people who had lived in or visited the United Kingdom, one each in the Republic of Ireland, Canada and the United States. Concern also extended to people who work with cattle meat and bone meal and may inhale it, such as horticulturists who use it as fertilizer.

  The epizootic was eventually brought under control by culling all suspect cattle populations. Even so, people are still diagnosed each year, though new cases have fallen to fewer than five annually. Prion diseases have incubation periods measured in years or decades, so the full extent of the human outbreak is still unknown.

  The Creutzfeldt-Jakob Disease Surveillance Unit requires reports of anyone in the United Kingdom with possible vCJD symptoms. In the United States, the CDC declined to require national reporting by physicians and hospitals. It relies instead on death certificates and on the National Prion Disease Pathology Surveillance Center at Case Western Reserve University in Cleveland, which the CDC funds.

  Blood donation rules followed the same worry. The FDA barred people who had spent a cumulative three months or more in the United Kingdom between 1980 and 1996, or five years or more in Europe between 1980 and 2020. Blood shortages during the 2020 COVID-19 outbreak led to a temporary suspension, and the recommendation was removed in 2022. Germany applies a similar rule, as did Australia in the past. It bars anyone who lived in the United Kingdom for longer than six months between 1980 and 1996. Breast milk and tissue donation are also barred, though organ donation is not restricted.

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• 6. Bovine Material In Medicine

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  On the 7th of May 1999, David Osborne Hagger gave a written statement to the BSE Inquiry. He was a retired civil servant who had worked in the Medicines Division of the Department of Health from 1984 to 1994. His account traced how the Medicines Control Agency, or MCA, dealt with BSE.

  In February 1989, the MCA was asked to identify relevant manufacturers and gather information on bovine material in children's vaccines. It also had to learn how large the stocks were and how long it would take to switch to other products. By July, officials had noted the use of bovine insulin in a small group of mainly elderly patients, for whom alternatives were not considered satisfactory.

  In September 1989, the BSE Working Party of the Committee on the Safety of Medicines recommended no licensing action for the time being. That covered products made from bovine material sourced outside the United Kingdom, the Channel Isles and the Republic of Ireland. The condition was that the country of origin was known to be free of BSE, had competent veterinary advisers and practised good animal husbandry.

  In 1990, the British Diabetic Association raised its own concern about the safety of bovine insulin. The committee assured it that no insulin sourced from cattle was in use in the United Kingdom or Ireland, and said the situation elsewhere was being monitored. The European Commission voiced concern in 1991 about possible transmission of the BSE and scrapie agent to people through certain cosmetic treatments.

  Then came 1992. Sources in France told the MCA that BSE had now been reported in France. Some licensed surgical sutures were derived from French bovine material. A committee meeting also raised the possible risk of transmission through gelatin products. France would later face harsh criticism over how it handled its own herds.

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• 7. Trade Wars

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  In March 1996, the European Union banned exports of British beef. The ban lasted ten years and was lifted on the 1st of May 2006, despite efforts by the British prime minister John Major between May and September 1996 to end it sooner. Trade disputes among European states were dubbed the beef war by the media. Restrictions stayed in place for beef containing vertebral material and for beef sold on the bone.

  France kept its own ban on British beef illegally, long after the European Court of Justice had ordered it lifted. It has never paid any fine for doing so. Russia began lifting its ban some time after November 2012, after 16 years, with the announcement made during a visit by the United Kingdom's chief veterinary officer, Nigel Gibbens.

  Northern Ireland made a special case for itself. It recorded only six cases of BSE in 1999, helped by an early herd tagging and computerization system, and calls grew to free its beef from the export ban. An exception was agreed for Welsh beef bound for the Dutch market.

  France was not blameless. A critic named Thillier asked why France had never banned French beef or taken basic precautions to protect its food chain. He suggested that the government had forgotten its role in guaranteeing food safety, and that the neglect cost the lives of nine people. The Sydney Morning Herald wrote that French politicians blamed Britain and banned British imports while failing to stop a hidden epidemic at home. The Economist noted that much of the crisis in Europe could be blamed on politicians and bureaucrats.

  On the other side of the world, Japan was the top importer of American beef, buying 1.7 billion dollars' worth in 2003. After the first United States case was discovered on the 23rd of December 2003, Japan halted imports. It allowed them again in December 2005, then reinstated the ban in January 2006 after a vertebral column was found in a shipment of veal. Japanese consumer groups said Tokyo had yielded to American pressure. Michiko Kamiyama of Food Safety Citizen Watch and Yoko Tomiyama of the Consumers Union of Japan said the government had put the political schedule between the two countries ahead of food safety and human health.

  Sixty-five nations imposed full or partial restrictions on American beef, doubting the rigor of its testing. Exports fell from 1,300,000 tonnes in 2003 to 322,000 tonnes in 2004. They recovered to 771,000 tonnes in 2007 and reached 1,300,000 tonnes by 2017. In April 2012, some South Korean retailers stopped importing American beef after a case was reported, and Indonesia suspended imports after a dairy cow in California was found with the disease.

  Japan itself recorded 36 confirmed cases, among the largest numbers outside Europe, and it was the only country outside Europe and the Americas to report non-imported cases. In 2003 it created a governmental Food Safety Commission. On the 31st of December 2006, the company Hematech, based in Sioux Falls, South Dakota, announced cattle produced through genetic engineering and cloning that lacked the gene for the PrPC protein, making them theoretically immune to BSE.

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• 8. Counting And Control

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  More than 184,000 cattle were diagnosed with BSE in the United Kingdom between 1986 and 2015, with new cases peaking in 1993. A few thousand more cases appeared elsewhere in the world. It is believed that several million infected cattle probably entered the food supply during the outbreak. About four million cows were killed in the United Kingdom's eradication programme. Only four cases were reported globally in 2017, and the condition is considered nearly eradicated.

  The main weapon was a ban on feeding meat and bone meal to cattle, which sharply cut cases wherever the disease had struck. In Britain, no animal older than 30 months may enter the human food or animal feed supply. In continental Europe, cattle over 30 months intended for human food must be tested. In North America, tissue of concern called specified risk material cannot go into animal feed or pet food. In British and American slaughterhouses, the brain, spinal cord, trigeminal ganglia, intestines, eyes and tonsils count as specified risk material and must be disposed of properly. The United States tightened its feed ban in 2009 and Canada did so in 2007. Countries without the disease rely on import controls, feeding rules and surveillance.

  Testing rules differ widely, which makes comparing numbers risky. In the European Union, cattle tested are 30 months or older, while many are slaughtered younger. Japan tests every animal at slaughter. Cases are classed as classic or atypical, and atypical cases split into H and L types.

  The first reported case in North America came in December 1993 from Alberta, Canada, and another Canadian case followed in May 2003. In December 2003 a cow of Canadian origin was slaughtered on a farm near Yakima, Washington, and became the first known United States case. Canada announced two more Alberta cases in early 2005. In June 2005, John R. Clifford, chief veterinary officer of the USDA Animal and Plant Health Inspection Service, confirmed a fully domestic case in Texas.

  The USDA announced on the 19th of May 2023 an atypical case in an older beef cow at a slaughter plant in South Carolina. It was the seventh detection in the United States since 2003, and all but one were atypical. American problems went beyond detection. The meat producer Creekstone Farms alleged in a lawsuit that the USDA was preventing it from testing its own slaughtered cattle. In 2007, Hallmark/Westland Meat Packing Company was found to have used electric shocks to prod downer cows into the slaughtering system, prompting beef recalls.

  In Europe, a case was confirmed on a farm in Carmarthenshire, Wales, in October 2015. France confirmed another in 2016. In October 2018, a case on a farm in Aberdeenshire was the first in Scotland in a decade. It was found through routine testing, and the cow never entered the food chain. Four other animals from the same herd were culled as a precaution. The most recent case in Britain was in May 2025, on a farm in Essex, and it too was atypical.

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