A new study from the University of Oxford has found that intensive poultry farming has dramatically accelerated the spread of Campylobacter, the world's most common bacterial cause of diarrhoeal illness. The research, published by the Ineos Oxford Institute for Antimicrobial Research, shows that the rise of industrial chicken production has led to a more than 100-fold increase in the transmission of this pathogen, which now poses a growing threat to public health across Europe and beyond.
By analysing roughly 2,800 bacterial genomes collected from chickens and wild birds in 30 countries between 1979 and 2024, the researchers traced how the transformation of bird populations has reshaped ecological niches. The global chicken population has surged sevenfold since the 1960s, reaching an estimated 31 billion birds today. This concentration of billions of birds into dense industrial systems has fundamentally altered the environment in which bacteria evolve and spread.
From wild birds to poultry flocks
Birds are known reservoirs for pathogens, and the study highlights how industrial farming has created one of the largest animal habitats on the planet. Bacteria that were once largely confined to wild birds now have far more opportunities to enter poultry flocks, become established, and adapt to life in crowded conditions. “Industrial farming has created one of the largest animal habitats on the planet. Our findings provide new evidence that human-driven environmental change can increase the spread of infectious diseases,” said Sam Sheppard, senior author of the study.
As chicken populations have grown, Campylobacter strains have gained new chances to jump from wild birds to poultry, where they can multiply and spread. The study notes that poultry are the foremost reservoir for human infection, with an estimated 60% to 80% of human cases attributable to isolates originating in chickens. This is particularly concerning for European consumers, where chicken is a staple protein across the continent, from French poulet rôti to German Hähnchen dishes.
According to the World Health Organization, Campylobacter is one of the four key global causes of diarrhoeal diseases. While infections are generally mild, they can be fatal among very young children, the elderly, and immunosuppressed individuals. Common symptoms include diarrhoea, abdominal pain, fever, headache, nausea, and vomiting, typically lasting between three and six days.
Antimicrobial resistance concerns
The study also raises alarms about antimicrobial resistance. As Campylobacter strains adapt to life in poultry, they can acquire traits that help them survive in challenging environments, including resistance to antibiotics. “Understanding how farming practices influence bacterial evolution is an important step towards reducing the burden of foodborne disease,” said Oakem Kyne, the study’s first author at the University of Oxford.
This issue is particularly relevant across Europe, where the European Centre for Disease Prevention and Control has been monitoring rising rates of antimicrobial resistance in foodborne pathogens. The findings come amid broader concerns about the spread of drug-resistant infections, such as the recent surge in antibiotic-resistant gonorrhoea cases across the continent.
The researchers emphasise that understanding the evolutionary consequences of industrial farming is essential for reducing future risks from zoonotic diseases and antimicrobial resistance. As Europe's poultry industry continues to expand, policymakers and public health officials face the challenge of balancing food production with the need to curb the spread of dangerous pathogens.
