Why should you read this chapter?

Diseases that pass between animals and humans are responsible for many of the diseases affecting people worldwide, especially in developing countries. Animals (wild and domestic) also play an important role in the emergence and spread of entirely novel human diseases, with the potential for large impacts on human health, such as bird flu. Another aspect of this to which livestock contribute, is the rise and spread of resistance to antibiotic drugs.

One outcome of sustainable food systems is that they should be health promoting. It is, therefore, useful to understand the interconnection between infectious diseases in human and animals, and how these risks may be amplified or reduced by changes in farming systems.

This chapter addresses the following:

  • How are infectious diseases in human and animals connected?

  • How does livestock farming affect human disease risk?

  • What is antibiotic resistance and why does it matter?

  • How does antibiotic use in livestock affect human health risks?

Key points

  • Zoonotic diseases are those where the pathogens that cause them, such as bacteria, fungi, parasites and viruses, are able to infect both humans and animals. They make up the majority of all known human infectious diseases.
  • Zoonotic diseases have a large impact on global health and are responsible for over 2.5 billion cases of human illness and 2.7 million human deaths worldwide each year, with most of the burden in low-income countries and among poor livestock keepers.
  • Livestock’s proximity to wildlife and humans (via the food chain) makes them an important point of interconnection for zoonotic disease transmission. Changes in livestock production and consumption can affect the health risks from zoonotic diseases.
  • Antimicrobials are compounds used to help kill pathogenic microbes. Antibiotics are antimicrobials, that target bacteria. Growth in antibiotic resistance threatens medicine’s ability to treat common infections and safely conduct medical procedures.
  • Resistance to antibiotics emerges as a direct result of their use. While a drug may kill most bacterial cells, a random genetic mutation in some may allow them to survive and proliferate. Bacteria can also exchange resistance genes with other bacteria that they encounter.
  • New antibiotic drug discovery is slow and costly, and is not currently keeping up with growing levels of antibiotic resistance. Antibiotics must be conserved to avoid a rise in untreatable infections and increased risks associated with medical procedures.
  • The majority of antibiotics worldwide (by weight) are used in livestock production – mostly given to pigs and poultry in intensive livestock production systems. Resistant bacteria are widely found in livestock populations. Many antibiotics used in livestock production are also those critical to human medicine.
  • Pathways for resistance transmission from livestock to humans are well understood, and good evidence exists for it taking place via the food system. However, it is not a simple step for resistance to be transferred from livestock to human pathogens, and then spread further.
  • Most clinical cases of antibiotic resistant infections in humans are thought to result from human use and misuse of antibiotics in hospitals and in the community. Limited and uncertain data, suggest that the current contribution from livestock is relatively limited.
  • Even with small probabilities of resistance transmission to human pathogens, over time and when scaled by the growing numbers of livestock worldwide, the long-term risk posed to public health from antibiotic use in livestock is still significant.
  • Given the potentially irreversible impacts and the alternative ways to reduce the burden of infection in livestock farming, delaying action to reduce antibiotic use in the livestock sector is seen by some as an unnecessary gamble on public health. Many governments, institutions and businesses are already taking action to restrict their use.

Credits

Suggested citation

Lee-Gammage, S., Atherton, E., Head, J., & Stewart, S. (2018). What is the connection between infectious diseases in humans and livestock? (Foodsource: chapters). Food Climate Research Network, University of Oxford.

Written by

Samuel Lee-Gammage, Food Climate Research Network, University of Oxford.

Contributing authors

Elizabeth Atherton, Medact.

Josephine Head, Medact.

Sarah Stewart, Medact.

Edited by

Tara Garnett, Food Climate Research Network, University of Oxford.

Website and graphic design

John Jackson, Food Climate Research Network, University of Oxford.

Reviewed by

Delia Grace, International Livestock Research Institute.

Andrew Singer, Centre for Ecology and Hydrology.

Reviewing does not constitute an endorsement. Final editorial decisions, including any remaining inaccuracies and errors, are the sole responsibility of the Food Climate Research Network.

Funded by

The production of this chapter was enabled by funding from the following sources:

The Daniel and Nina Carasso Foundation

The Esmée Fairbairn Foundation