Human, livestock and environmental health are inextricably linked. Sixty-one per cent of all diseases are ‘zoonotic’—that is, transmissible between animals and humans. Such zoonoses include common food-borne illnesses as well as fatal infections with rabies and anthrax. Many of our important current human diseases, such as HIV-AIDS, measles and smallpox, were originally diseases of animals that ‘jumped species’ when people changed their ways of farming and keeping animals.
Unprecedented levels of globalization, urbanization, animal production and environmental degradation are driving new epidemics of infectious diseases, both familiar and new. One new disease is emerging every four months, and 75% of these new diseases originate in animals. But besides creating such big risks to human health, animals, especially livestock, also provide big benefits to people, including food, fibre, fuels and raw materials.
Livestock farming systems cover one-quarter of the global land, livestock value chains employ 1.3 billion people and at least 600 million of the world’s poor depend directly on livestock for their livelihoods. Consumption of even modest amounts of milk, eggs, fish and meat is a good way to manage the ‘hidden hunger’, or micro-nutrient deficiency, that impairs the health and lowers the capacity of some 1.2 billion people. Regarding human health and nutrition, livestock in poor countries represent two mixed messages.
First, rapidly developing countries—with their rich biodiversity, booming human populations, evolving agri-food systems and high animal densities—are hot spots for emerging infectious diseases. At the same time, neglected human populations in these and some of the least developing countries continue to suffer from neglected diseases that are easily managed.
Second, animal-source foods are excellent sources of nutrients for people—and for pathogens. Most diarrhoea, for example, which remains a major cause of sickness and death in poor countries, is due to contaminated food. With both the harms and goods at the intersection of livestock and human health being enormous and complex, research is helping to maximize the health benefits and minimize the health risks of animal agriculture for people.
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