Intended for healthcare professionals


Bovine spongiform encephalopathy: its wider meaning for population health

BMJ 1996; 312 doi: (Published 25 May 1996) Cite this as: BMJ 1996;312:1313
  1. A J Mcmichael
  1. Professor of epidemiology Department of Epidemiology and Population Sciences, London School of Hygiene and Tropical Medicine, London WC1E 7HT

    Worldwide intensive meat production is unsustainable

    Evidence from Britain that the agent causing bovine spongiform encephalopathy in cattle may cause neurological disease in beef eaters1 and the consequent turmoil in the beef trade have made compelling headline news across Europe. The ecological dimensions to this public drama have, however, even wider implications for population health.

    Three issues warrant discussion. Firstly, although the infective agent of bovine spongiform encephalopathy and its effects may seem exotic, this episode merely extends the long running narrative whereby changes in human culture induce new infectious diseases. Secondly, the method of cattle feeding implicated in the transmission of bovine spongiform encephalopathy seems partly to have arisen because of supply-demand pressures in the world food production system. Thirdly, the scare about bovine spongiform encephalopathy is the tip of a much larger iceberg of adverse environmental and health consequences of the mass production and consumption of meat.

    Firstly, incredulity that the mysterious transmissible agent responsible for bovine spongiform encephalopathy might “jump species” and infect humans is misplaced. Microbes and their ilk are no less opportunistic than any other species—and are capable of rapid genetic adaptation.2 We humans have improved our survival prospects by widening the range of other species on which we feed. Bacteria and multicellular parasites do likewise, as do the viruses and prions that parasitise the intracellular molecular processes of animals and plants. Ever since humans made intimate contact with other animal species—by intruding on their habitats, eating them, or domesticating them—mutant strains of zoonotic agents have opportunistically become infectious agents in humans.3 4 Thus have we acquired smallpox from cattle, measles from ungulates or dogs, influenza from pigs, HIV from monkeys, and so on.

    This endless narrative is a condition of life on earth: it is simply anthropocentrism that sees many tiny species as “pests and diseases” because they share our food supplies or parasitise us. Modern intensive methods of agriculture, animal husbandry, and aquaculture have opened up vast new ecological opportunities for microbes.4 5 Hence it would be surprising if transmission of the type that we think may be happening with bovine spongiform encephalopathy and Creutzfeldt-Jakob disease did not occur.6 Recent sequencing of the prion protein in vertebrates indicates an evolutionary connection between the forms in cattle and in humans.7

    Secondly, modern methods of intensive farming reflect increasingly the tension between food supply and demand. As populations have increased in size and affluence, so the demand for food has grown, particularly for foods such as meat that are seen as high quality. The expectation of cheap meat, helped by competition between supermarkets and government subsidy, is spreading throughout the world's middle classes. The resulting intensification in meat production requires heightened inputs of energy, chemicals, water, and protein feed.8

    The use of protein derived from ruminants for cattle feed increased in the early 1980s, as world prices escalated for the then prevailing protein supplements, fishmeal and soybeans. The price rises reflected faltering growth in per capita production of those foods, after three decades of strong growth.9 10 The per capita production of soybeans tripled between 1950 and 1980 while the per capita fish catch doubled between 1950 and 1970, but neither has increased further since those peaks. From the 1980s the growth in production of these and several other foods seems to have fallen behind the growth in world population.1011 We must therefore ask of our recent methods of food production: to what extent have we been depending on unsustainable resource inputs? And of the future: can we sufficiently boost production with genetically engineered plant, animal, and marine foods? The answers bear strongly on the long term prospects for human health.

    Thirdly, beef production is a very environmentally damaging form of meat production.8 If we are adequately and equitably to feed a world of 10 billion people next century, compared with today's 5.7 billion, then beef-eating Westerners cannot expect to continue dining at an elite high table. There is insufficient land and protein supplement (whether as cereal, fish, or mammalian scraps) to enable a beef enriched global diet. The supplies of fossil fuel energy and water required for intensive livestock production are huge. So is the demand for forests to be denuded to create pastoral land in Central America to produce lean beef for McDonald's burgers.12 A unit of beef energy produced in western (and, increasingly, east Asian) factory farms requires an input of around 6-7 units of cereal grain energy.8 Smil argues that “diets high in meat are a very recent aberration unsustainable on a global scale.”11

    Epidemiological studies indicate that vegetarians live a little longer than meat eaters.1314 We should therefore expect that a world diet of modest meat content would bring widespread gains in human health—both directly and by averting the adverse social and environmental consequences of intensive meat production.14

    These complex ecological issues portend far reaching and challenging policy decisions. Currently, however, we are preoccupied with the unsettling risks to public health from British beef already eaten. And in the political arena the findings of the parliamentary Joint Agriculture and Health Select Committee seem unlikely to go beyond the puny immediacies of economic and political face saving. We thus risk overlooking the wider ecological and public health implications of our mass produced, meat enriched diet. For over one hundred millennia food supplies and, more recently, food production methods have been central to the ecological sustainability of human societies.5 In the coming millennium we will need to think even more in those terms.


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