Intensive farming, where animals are kept in close quarters, creates environments that encourage the evolution of harmful bacteria and other pathogens so that they gain traits making it easier to infect people and more difficult to cure, a new study suggests.
Hygiene and welfare standards are often low on industrial farms, also called factory farms, and the rising widespread use of antimicrobials has led to concerns that overuse in animal farming is playing a key role in driving antimicrobial-resistant infections in people.
To gain insights into how intensive animal farming influences the evolution of harmful bacteria, a new study investigated how modern densely populated chicken farms have shaped the evolution of strains of Campylobacter jejuni bacteria, which are the leading cause of gut illness and diarrhea from bacterial food poisoning in people, typically after eating contaminated chicken.
Chickens are of particular interest because populations have shot up sevenfold since the 1960s due to agricultural growth and increasing demand for poultry. Today, roughly 31 billion chickens inhabit the globe. Together, poultry accounts for around 70% of all bird biomass on Earth.
The results showed that C. jejuni evolved rapidly in chickens, developing genetic strains resistant to antimicrobials and more likely to adapt to other species, which makes it easier for them to infect people.
Published in the peer-reviewed journal Proceedings of the National Academy of Sciences, researchers from the universities of Oxford and Sheffield in the United Kingdom analyzed the genetic information of 2,747 C. jejuni samples from wild birds and chickens.
They found that since 1900, the transmission between chickens and wild birds has increased by more than 100-fold.
Farming intensification has changed how pathogens interact between populations of wild birds and domesticated chickens, says Oakem Kyne, a lead researcher on the study at the University of Oxford.
There is a much wider variety of chicken-adapted C. jejuni strains now than before they were domesticated, with a large jump since 1900 when modern poultry farming intensified, says Kyne.
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