Cow 133: How we created a monster in the food chain

By Dr Maria Pannell

Three days before Christmas in 1984, vet David Bee was called out to visit Pitsham Farm, just south of Midhurst in Sussex. The farmer was concerned about one of his cattle. It had been displaying a range of bizarre symptoms that neither he nor the vet had ever encountered: aggression, head tremors, an arched back, difficulty walking, and extreme thinness. The condition was initially called Pitsham Farm Syndrome, and the animal ‘Cow 133’. By spring, six animals were dead, fed to the dogs of Petworth Hunt. Bee began to suspect mercury or lead poisoning - but tests came back negative, same for organophosphates. By August, the last two cows died and the strange condition never reappeared at Pitsham. It was not the end. What the animals were suffering from would later become known as Bovine Spongiform Encephalopathy (BSE) or mad cow disease (1).

Anyone who was around in the late ‘80s and early ‘90s will remember the news reports: the grainy videos of cattle stumbling, shaking, crawling in the mud; the politician feeding a hamburger to his young daughter to reassure the public that British beef was safe. BSE reached its peak in 1992 with more than 30,000 cases (2) and now seems like a distant memory. But what caused the crisis? Is it really over? When I was 23, I began working as a pathology scientist at the Veterinary Laboratories Agency (VLA) in Surrey. I was working on animal studies involving cattle and sheep that had been inoculated with varying strains of BSE and scrapie. When I started at the VLA I knew little about Creutzfeldt-Jakob disease (CJD), BSE or scrapie. We learnt nothing about them during A-level biology or at university. I had no idea that they were caused by prions, glycoproteins found within every cell of the human body, but particularly dense in the central nervous system. The precise function of the prion protein remains elusive, though it has been demonstrated to have a role in several processes such as neuritogenesis, neuronal homeostasis and cell signalling (3). The normal, cellular prion protein in unaffected individuals is referred to as PrPC, for cellular. This protein features a disorganised “floppy” N-terminus involved in copper binding, and an organised C-terminus, with a structure featuring three alpha-helices and 2 beta-sheets (4), as well as a glycosylphosphatidylinositol (GPI) anchor which fixes the protein to the cell surface (5). In prion disease, the native PrPC converts into a misshapen, insoluble form known as PrPSc. During this process, there is an increase in beta-sheet content, which causes the insolubility as well as partial resistance to enzymatic degradation. This results in an accumulation of PrPSc, which is deposited inside as well as outside the cell. Aggregates act as a template for conversion of native PrPC, with smaller PrPSc fragments exhibiting the highest rate of infectivity and conversion (6). In the UK, the most common form of prion disease in humans is sporadic Creutzfeldt-Jakob disease (sCJD), which occurs without a known trigger, and makes up 85% of cases (7). In 2020, there were 131 recorded deaths from sCJD (8). Cases of variant CJD (vCJD), primarily contracted through consumption of contaminated meat or through blood transfusion, were first identified in 1996.

Following the cattle deaths at Pitsham in 1985, the brain of a euthanised animal had been sent to the UK's Central Veterinary Laboratory (CVL) for analysis (later named the VLA and currently the Animal and Plant Health Agency (APHA)). A pathologist named Carol Richardson examined the brain of this animal and noticed the “spongy” holes in the tissue characteristic of a spongiform encephalopathy. She left the slides on the desk of a colleague for a second opinion and went to lunch. Her colleague, Dr Martin Jeffrey, examined the slides, leaving them on her desk with a note: “Bovine Scrapie”. Scrapie was a well-known disease of sheep and the oldest known member of the group of transmissible spongiform encephalopathies (TSEs), along with BSE, CJD, and Chronic Wasting Disease (CWD) of deer (among others). It was first described around 1732 in sheep, and in 1936 was shown to be transmissible from sheep to sheep (9). In 1982, the term “prion” was coined by Stanley Prusiner, who proposed the ‘protein-only’ hypothesis to explain the infectious agent in this disease. He was later awarded the Nobel Prize for his discovery (10). Scrapie had been around for centuries though, and was never known to jump species. In the 20th century, it was common practice in the UK, as well as other countries, for farmers to feed livestock with protein-rich rendered animal carcasses. It was seen as an efficient and economical method of boosting farm-animal growth and using up animal waste not fit for human consumption. This product was known as Meat and Bone Meal (MBM). It was added to commercial feed pellets and sold to farmers. This turned herbivorous cattle into cannibalistic consumers of meat, as the pellets contained both bovine (cow) and ovine (sheep) protein. The link between these pellets and the BSE epidemic was first reported in 1988 (11). It was believed that temperature changes in the rendering process in the 1970s allowed the highly resilient prion protein to survive. Later, BSE-infected cattle were also added to the MBM, continuing and amplifying the cycle (12).

Following the identification of ‘Bovine Scrapie’ in 1986, the head of pathology at the CVL, Ray Bradley, wrote the following in a memo to colleagues: “If the disease turns out to be bovine scrapie it would have severe repercussions for the export trade and possibly also for humans… I recommend playing it low key” (13). The memo led to an internal six-month embargo on publishing or sharing BSE-related information with the wider scientific community. For the next 18 months, farmers were allowed to sell infected meat to the general public and for export (14). As scrapie had never been a danger to humans, it was believed that BSE would be similarly without risk. In July 1988, the first regulatory measures were finally implemented - a ban on feeding ruminant-derived protein and MBM to other ruminants. BSE was then made a notifiable disease which required farmers and vets to report suspected cases resulting in compulsory slaughter and destruction of these cattle (15). High-risk tissues such as the brain, spinal cord and spleen were removed from the human food chain (16). Even in light of these measures, the government still did not acknowledge the risk to humans of eating infected beef. In 1990, BSE jumped species when a cat caught it from contaminated cat food (17), but still the government continued its campaign of reassurance in order to manage public perception and prevent panic. This included the infamous video of Agriculture Minister John Gummer feeding a hamburger to his four-year-old daughter Cordelia in front of national media. In 1996 the penny finally dropped. In the summer of 1994 an 18-year-old man named Steven Churchill was involved in an inexplicable car accident where he drove head-on into an oncoming truck. He had no memory of the incident. In the months following he slipped into a deep depression and left school. Following a lunch out with his mother, he admitted he had no memory of the meal. Doctors diagnosed depression. By Christmas he was losing coordination and could no longer sign his name. Upon admittance to hospital in the New Year, he was finally diagnosed with vCJD. He died on May 21st, 1995 (18). In March 1996, the Secretary of State for Health, Stephen Dorrell, finally admitted in Parliament the horrifying truth - that 10 people had contracted vCJD and that it was linked to the BSE outbreak. Four of these cases were dairy farmers with infections in their herds. Following this, the EU imposed a ban on British beef which continued for 10 years (19). In subsequent years, more comprehensive control measures were introduced including the removal of animals over 30 months from the food chain, due to a higher risk of them incubating BSE. Millions of animals were destroyed. From 1997, beef was banned in over 2,000 schools. Mouse studies confirmed the link between vCJD and BSE (20). In 2013, scientists estimated that 1:2000 people in the UK may carry variant CJD proteins (21).

To date, vCJD has killed 178 people in the United Kingdom (22). While this number is thankfully lower than the tens of thousands predicted in the panic of the nineties, it represents a profound human tragedy. These were not elderly patients at the end of a long life; they were young people like Steven Churchill, struck down in their prime by a man-made catastrophe. But the question remains: if millions of us were exposed to infected beef during the covert spread of the late 80s, why have deaths stalled?

The answer may lie in our genetics. All clinical cases of vCJD so far have occurred in people with a specific genotype: methionine homozygotes at codon 129 (23). It is terrifyingly plausible that those with different genetic backgrounds are not immune, but simply have a longer incubation period. In Kuru, a prion disease transmitted by cannibalism in Papua New Guinea, incubation periods of over 50 years have been documented (24). The "end" of the BSE crisis may simply be the eye of the storm. The prions could be lying dormant in thousands of carriers, potentially transmissible via blood transfusion or surgery, waiting for the clock to run down.

Despite this lingering biological time bomb, our legislative memory is proving short. For decades, the ban on MBM was the safety net created to protect us against further man-made horror. Yet, in 2021, the UK and EU relaxed these bans, allowing pig to be fed to chicken and chicken to be fed to pig, while rebranding the practice as “Processed Animal Protein” (PAP) (25). While the ban on ruminant-to-ruminant feeding remains, critics argue we are re-opening the door to cross-contamination and the recycling of pathogens. We are smashing down the walls built to keep us safe.

This speaks to a broader, uncomfortable truth about our relationship with food. The BSE crisis was born from a desire to turn nature into a machine, forcing herbivores to become carnivores to satisfy humanity's never-ending desire for low-cost meat. Today, facing a cost-of-living crisis, this pressure is higher than ever. Whether it’s chlorinated chicken imported from thousands of miles away, or the intensive farming of pigs in conditions ripe for zoonotic spillover, we continue to prioritise price over principles.

BSE taught us that the food chain is not a factory line where inputs and outputs are isolated; it is a biological loop. When we cut corners on biology to save money on economics, the cost is eventually paid in human health. The cattle are gone, and the grainy news footage has faded, but the prions, indestructible and patient, remain. We can only hope we haven't forgotten the lesson they tried to teach us.

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24. TBC
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