Industrial chicken farms are fuelling the spread of diarrhoea-causing bacteria, study finds

Industrial poultry farming has led to a more than 100-fold increase in the spread of Campylobacter, the most common bacterial cause of gastroenteritis in the world, according to a new study by the University of Oxford.Intensive poultry farming has transformed global bird populations, concentrating billions of chickens into dense industrial systems that fundamentally reshape ecological space, researchers at Ineos Oxford Institute for Antimicrobial Research said, after analysing around 2,800 bacterial genomes from chickens and wild birds in 30 countries between 1979 and 2024.Birds are significant pathogen reservoirs and these changes can have important consequences for the spread of infectious diseases jumping from animals to humans. The number of chickens has risen sevenfold since the 1960s to roughly 31 billion birds today, the authors said, increasing the risk of environmental spillover of different diseases into the human food chain. “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, bacteria that were once largely confined to wild birds have gained far more opportunities to enter poultry flocks, spread and become established, he added.“Understanding these evolutionary consequences is essential if we are to reduce future risks from zoonotic disease and antimicrobial resistance.”Campylobacter is one of the four key global causes of diarrhoeal diseases, according to the World Health Organization. Infections are generally mild, but can be fatal among very young children, the elderly, and immunosuppressed individuals. The most common symptoms of Campylobacter infections include diarrhoea, abdominal pain, fever, headache, nausea and vomiting; symptoms typically last between three and six days. Poultry are the foremost reservoir for human infection, with an estimated 60% to 80% of cases attributable to isolates originating in chickens, the study noted. “As Campylobacter strains adapt to life in poultry, they can acquire traits that help them survive in challenging environments, including traits linked to antimicrobial resistance,” said Oakem Kyne, the study’s first author at the University of Oxford. Antimicrobial resistance is a growing public health concern, as it threatens the effectiveness of current treatments.“Understanding how farming practices influence bacterial evolution is an important step towards reducing the burden of foodborne disease,” added Kyne.