Mad cow disease: threat of an epidemic
By Michael Greger
Peter Hall showed the first signs of depression around Christmas 1994. In five months he was in a wheelchair. He died at age 20 of Creutzfeldt-Jacob disease (CJD), a relentlessly progressive and invariably fatal dementia which usually attacks people in their sixties; cases under 30 are exceedingly rare. Around the next Christmas, an uproar ensued when leading British neuropathologist Sir Bernard Tomlinson refused to feed his children hamburgers out of fear that they might contract this disease from infected beef. His fears were realised on March 20, 1996, when the British government announced that the most likely explanation of Peter's death and nine other recently diagnosed cases of CJD among English young people was exposure to bovine spongiform encephalopathy (BSE).
The first documented case of BSE occurred in 1985. Dubbed mad cow disease by the British press, BSE has by now stricken more than 150,000 cattle. The fear now is that through the consumption of infected beef, Britain may be on the brink of the largest public health calamity since the Black Death.
CJD is a human spongiform encephalopathy whose standard clinical picture involves weekly deterioration into blindness and epilepsy while one's brain perforates like Swiss cheese. The World Health Organisation recently agreed with the British government's conclusion that there is a new variant of CJD whose appearance is best explained by the BSE epidemic in cows because of a number of consistent unusual features. Other than being extraordinarily young, the human victims also had atypical EEGs and took twice as long to die.
The real clincher came, though, when their brains were autopsied. The brain pathology was found to be vividly reminiscent of kuru, a disease found in a New Guinea tribe of cannibals which ate the brains of their dead.
The infectious agents that cause spongiform encephalopathies like CJD and BSE evoke no immune response and consequently may slowly accumulate for an invisible latency period of up to 30 years. No-one knows how many people have already been infected. John Pattison, dean of the University College of London Medical School and Chairman of the British government's Spongiform Encephalopathy Advisory Committee (SEAC), thinks there could be 500,000 people already incubating CJD.
Microbiologist Steven Dealler, secretary of the Spongiform Encephalopathy Research Campaign, places the possible death count at 2 million people. Professor Pattison reportedly agreed with this worst case scenario assessment. This could mean up to a half million deaths a year as the epidemic peaks into the next century, according to Richard Lacey, a microbiology consultant for the World Health Organisation and child health specialist.
It is now close to being generally accepted that the cause of the disease in both humans and cows isn't a virus or a bacteria, but a "prion", an infectious protein. Not only is it not known how they replicate, but the whole concept challenges the basic tenets of biology.
Because of their unique make-up, prions are practically invulnerable. They are not adequately destroyed by cooking, canning or freezing. Chemicals or enzymes which degrade nucleic acids, proteolytic enzymes of the digestive tract and useable doses of UV or ionising radiation are all ineffective in destroying their infectivity. Even heat sterilisation, domestic bleach and formaldehyde sterilisation have little or no effect. In fact, the only way to ensure that one's burger is safe is to marinate it in Drain-O (or other concentrated alkali).
Widespread fear first struck in 1989. Only months after the government concluded that the disease probably wouldn't spread to other species, Max, someone's pet Siamese, died of a hitherto unknown feline spongiform encephalopathy. BSE-infected pet food was the most likely explanation. Then zoo animals started dropping dead.
By May 1990, a quarter of the population reportedly refused to eat beef. In six months beef prices dropped 10-25%.
After a $6.5 million advertising campaign touting red-meat consumption, from Britain's Meat and Livestock Commission, though, and the minister of agriculture munching burgers with Cordelia, his four-year-old daughter, for the TV cameras, the schools put beef back on the menu and beef consumption regained semi-normal levels.
Six months ago Britain's prime minister was still asserting that there was absolutely no connection between BSE and CJD; he still attempts to reassure the public that beef is safe to eat to this day. Likewise the USDA [Department of Agriculture] continues adamantly to parrot day after day that there is no BSE in the USA.
The United States has the highest per capita beef consumption in the world. Traditional BSE hit North America in 1993. The first cow discovered to be infected, one of many imported from the UK before both Canada and the US banned the importation of British cattle, was found on a ranch in Alberta, Canada.
Of the 499 British cattle imported into the US before the 1989 ban, 188 were melted down into lard and protein (presumably for other livestock to eat) and 35 remain unaccounted for. One of the imported bulls slaughtered had a "central nervous system abnormality" of which the USDA reported, "There is no definitive evidence that [the bull] either had or did not have BSE".
Although the importation of British beef has been banned from the US for a decade due to an unrelated disease, 12 tonnes of meat and bone meal, which has been implicated in the birth of the British epidemic, came into the US from England between 1982 and 1989.
BSE was almost certainly caused by feeding cattle ground-up sheep infected with an ovine spongiform encephalopathy known as scrapie. In modern agribusiness, cows are no longer herbivores. "Protein concentrates" (or meat and bone meal, both euphemisms for mashed-up bits of other animals left over from the slaughterhouse) are fed to dairy cows. The real problem now, though, is not that we've made cows meat eaters but that we've turned them into cannibals as well; the recycling of the remains of infected cows into cattle feed has probably led to the epidemic's explosive spread.
Indigenous conditions in the US conducive to a BSE outbreak include the presence of scrapie in 39 states. The 40-year USDA Scrapie Eradication Program has been deemed a "dismal failure" and even implicated in the recent rise of scrapie-infected sheep. Admitting defeat, the USDA scrapped the Scrapie Eradication Program two years ago and replaced it with an "entirely voluntary" control program.
Since 1947 there have been 25 outbreaks of mink spongiform encephalopathy (also called TME) on US fur farms. This perplexed researchers, who were unable to orally infect mink with scrapie-infected sheep brains. A clue came in 1985 when TME wiped out a population of minks in Wisconsin which hadn't eaten any sheep. Their diet consisted almost exclusively of dairy cattle called "downers", an industry term describing a syndrome in which cows mysteriously drop down and are too sick to get up.
The possibility that US dairy herds were harbouring some form of BSE intrigued University of Wisconsin veterinary scientist Richard Marsh. To test this, Marsh inoculated US cattle with the infected mink brains. As predicted, they died. And when he fed the brains of these cows to healthy mink, they too died of a spongiform encephalopathy, providing what he thought was the missing link.
Marsh hypothesised that the proposed BSE strain indigenous to the US manifests itself as more of a downed cow disease than a mad cow disease. With about 300,000 cows going down for unexplainable reasons every year in the US, this has frightening implications on a grand scale. The downer cow is then melted down in a process called rendering into feed and her bones are boiled (along with her skin and cartilage) to make gelatine.
The critical experiment came when Marsh inoculated scrapie-infected sheep brain into US cattle. If you do this in England the cows go mad, twitching and kicking into a rabid frenzy. But in America, cows instead stagger to their deaths like downer cows do, supporting the belief that a form of BSE is already in the United States.
By 1990 the USDA had 60 labs monitoring US cattle herds for BSE. In 1991 APHIS, the governmental agency which ensures the health of the nation's livestock, concluded that the "possibility of BSE appearing in US cattle is extremely low". The assumption made by APHIS and others, however, was that "scrapie-infected sheep were the only source of the BSE agent". This is certainly questionable in light of the evidence for an indigenous BSE agent.
In June 1992 a USDA consultant group continued to disregard the available evidence, deciding that changes in the research program to accommodate the possibility that BSE was already present in the US were "not appropriate at this time". No surprise really, when one realises that this panel included representatives of the National Milk Producers Federation, the National Renderers Association, the American Sheep industry Association and the National Cattlemen's Association. According to a newspaper report, though, in 1993 the USDA finally backed down and started testing downer cows.
In all, 2660 brains from 43 states have been examined by APHIS, with plans to increase the number. They report that no evidence for BSE has been found. Unfortunately, they were evidently relying on standard techniques used by British officials. As reported in the April 1994 issue of the Journal of Infectious Diseases, not only does the suspected US version of BSE differ in outward appearance, the affected brain also looks different from the British variety.
In Germany, scientists have admitted that there have been many cases of BSE that were not reported. It was reported in the Sunday Telegraph that "British officials believe that some European countries concealed or ignored evidence of 'mad cow disease' for fear of the consequences for their own farming industries".
The problem, as many English pundits saw it, is that the Ministry of Agriculture, Fisheries, and Food represents the interests of both consumers and the beef industry. A similar conflict of interest exists in the United States. The mandate of the USDA is to promote agricultural products but also to protect consumer health.
Like England, the US has been feeding dead cows to living cows for decades. In fact, in the US a minimum of 14% of the remains of rendered cattle is fed to other cows (another 50% goes on the pig and chicken menu). In 1989 alone almost 360 million kilograms of processed animals were fed to beef and dairy cattle. Partly because of this, the USDA has conceded that "the potential risk of amplification of the BSE agent is much greater in the United States" than in Britain.
According to top encephalopathy expert Joseph Gibbs, one out of every million cattle naturally develops BSE. A single teaspoon of ingested high infectivity meat and bone meal is thought to be enough to cause BSE in a cow. Between this and evidence that prions may be able to adapt to their hosts and become more virulent with time, it would seem absolutely necessary to stop recycling this disease through US cattle.
In June 1993 the Foundation on Economic Trends, a Washington public interest group, petitioned the FDA to ban all feeding of ruminants (cows, sheep) to other ruminants, as the European Community had done three years before. The legal petition was largely ignored.
The next year the FDA did propose to at least stop feeding sheep offal to cows, but it was blocked by vehement protests from the rendering and livestock industries.
On April 3, the World Health Organisation called for a worldwide ban on feeding animal tissues to livestock. The FDA has promised to "expedite" such regulations. This is expected to mean that putting a formal ban in place will take 12 to 18 months. Even with the law in Britain, though, surprise random inspections last year showed half of the English slaughterhouses in violation of the cow to cow ban regulations.
For every "mad" cow incinerated in the UK, there may be hundreds slaughtered and sold to butchers before any overt symptoms develop. Narang estimates that a third of all English cattle going into the food chain are infected with BSE.
Because of this, it is estimated that every adult in the UK has eaten on average 50 meals containing tissue from infected cattle. In the Journal of Public Health Medicine, Dealler, the microbiologist, wrote that in all probability most humans who have consumed British beef since the start of the BSE epidemic will have been exposed to the infection.
In the US it may be even harder to stop infected cattle from entering the food supply since dairy cattle are routinely culled earlier than in Britain.
Just because someone consumes an infectious dose of BSE, though, does not mean that they will necessarily get the disease. There is still no direct proof that BSE can even cause CJD in humans. The recent deaths in Britain may turn out to be unrelated to beef consumption.
BSE has been able to infect and (therefore) kill cats, antelopes and even ostriches from presumably eating infected protein, however. Eighty cats have now followed Max to the grave. Experimentally, one can give BSE to monkeys, pigs, chimpanzees and 13 other species. There really is no reason to believe that BSE will not similarly infect humans.
Cows aren't the only possible source of prion disease. Paul Brown, medical director of the NIH [National Institute of Health] neurological disorders institute with the US Public Health Service, believes that pigs and poultry could be harbouring BSE and passing it on to humans, adding that pigs are especially sensitive to the disease. "It's speculation", he says, "but I am perfectly serious".
On March 20, the British government banned farmers from feeding processed cattle blood, bones, fat and offal to pigs and poultry. A week and a half later it even halted the use of meat and bone meal as agricultural fertiliser.
If indeed a form of BSE is in the United States and causing disease among meat eaters, one would expect to see an increase in Creutzfeldt-Jacob disease. CJD, however, is not a reportable illness, so a rise similar to the one in Britain could be missed.
CJD is seriously underdiagnosed at present. The most common misdiagnosis of CJD is Alzheimer's disease. Both diseases show overlapping symptoms and pathology. There can be spongy changes in Alzheimer's and amyloid plaques in CJD. In fact, the brains of the young people who died from the new CJD variant in Britain look like Alzheimer's brains. Stanley Prusinger, the scientist who coined the term prion, believes Alzheimer's may even turn out to be a prion disease.
The true prevalence of prion diseases remains a mystery. An informal survey of neuropathologists registered a theoretical range of 2-12% of all dementias as actually CJD, whereas the official rate in the US is less than 1 case in a million per year.
Four million Americans are affected by Alzheimer's; it is the fourth leading cause of death among the elderly in the US. A preliminary 1989 study at the University of Pennsylvania showed that over 5% of patients diagnosed with Alzheimer's were actually dying from a human spongiform encephalopathy. That means that as many as 200,000 people in the United States may already be dying from mad cow disease each year.
Assuming a 10-year incubation period, all of the young people dying of CJD in Britain over the last few months were presumably infected when there were only a few hundred infected cows being turned into beef. In the year 1990 alone, it is estimated that 250,000 BSE-infected cows were eaten, which of course raises the question how many people might be dying at the turn of the century.
A 1991 internal USDA document entitled "BSE: Rendering policy", retrieved through the Freedom of Information Act, weighed the costs and benefits of a number of preventive measures, including a total ban on feeding ruminants to ruminants. The supporters of this option felt that this minimised the risk to public health.
APHIS, however, goes on to explain that the "disadvantage" of this approach is "that the cost to the livestock and rendering industries would be substantial". The lost revenue to cattle producers of such a ban is estimated at a dollar per cow.
The archbishop of York recently blamed the BSE epidemic on greed and profit. Other than simply corporate profiteering, this crisis shows to what length governments will go to prevent financial harm to powerful lobbies, and in doing so risk immeasurable harm to those they claim to represent.