Industrial chicken farming is significantly accelerating the spread of campylobacter, the world's most common bacterial cause of diarrhoea, according to a new study. Researchers found that the intensive nature of modern poultry production creates an ideal environment for the bacteria to evolve and spread, leading to concerns about public health and the increasing challenge of treating infections.
The study, led by Professor Sam Sheppard of the University of Oxford, revealed a dramatic increase in the exchange of campylobacter strains between wild birds and farmed chickens. This intensified interaction allows different bacterial strains to mix, leading to the development of new characteristics and, critically, a rise in antimicrobial resistance traits. Professor Sheppard described the phenomenon as chickens becoming a "cauldron of bacterial evolution," where new, potentially more dangerous strains can emerge.
Campylobacter is responsible for over three times as many gastroenteritis cases in the UK annually as all other monitored foodborne bacteria combined, with an estimated 60-80% of these infections originating from raw chicken. While most individuals recover without specific treatment, some cases require antibiotics. The growing prevalence of antimicrobial resistance means that previously effective drugs are now failing to treat some campylobacter infections, raising the risk of more severe illness and complications like irritable bowel syndrome.
Published in the journal Proceedings of the National Academy of Sciences, the research analysed nearly 2,800 bacterial genomes collected from chickens and wild birds across 30 countries, including the UK, US, and China, between 1979 and 2024. This extensive dataset allowed scientists to reconstruct the evolutionary pathways of diverse campylobacter strains. They discovered an estimated 100-fold increase in the movement of strains between chickens and wild birds since 1900 compared to pre-domestication periods, a trend that has sharply escalated in recent decades.
The scientists attribute this acceleration to the unprecedented scale of global chicken production. Since the 1960s, the global chicken population has surged seven-fold to approximately 27 billion birds, now comprising about 70% of all bird biomass on Earth. This industrialisation, while making animal protein more affordable and accessible, has inadvertently created new health risks. The study also identified specific genetic changes in campylobacter that enable it to adapt to the chicken farming environment, including genes linked to antimicrobial resistance, which are further encouraged by the routine use of antibiotics in poultry farming for growth promotion and disease control.