Key facts
- Industrial poultry farming is accelerating the spread of Campylobacter, the most common bacterial cause of diarrhea globally.
- A study found a 100-fold increase in the movement of Campylobacter strains between wild birds and chickens since 1900.
- Intensive chicken farming creates conditions for bacteria to mix, spread, and acquire new traits, including antimicrobial resistance.
- Global chicken populations have grown seven-fold since the 1960s, now comprising 70% of all bird biomass.
- The research analyzed nearly 2,800 bacterial genomes from chickens and wild birds across 30 countries.
Industrial chicken farming is significantly accelerating the spread of Campylobacter, the world's most common bacterial cause of diarrhea, scientists have found. A study published in the Proceedings of the National Academy of Sciences analyzed nearly 2,800 bacterial genomes from chickens and wild birds across 30 countries between 1979 and 2024.
The research indicates a dramatic increase in the exchange of Campylobacter strains between wild birds and chickens, with an estimated 100-fold rise in transitions since 1900 compared to pre-domestication levels. This intensification of farming has created ideal conditions for the bacteria to mix, spread, and evolve, including acquiring traits associated with antimicrobial resistance.
Professor Sam Sheppard of the University of Oxford, a senior author of the paper, stated that the exploding chicken population has turned them into a "cauldron of bacterial evolution." He warned that the scale of production poses a massive risk to human health, as new 'Frankenstein monster bugs' could emerge.
Campylobacter causes more than three times as many gastroenteritis cases in the UK annually as all other monitored foodborne bacteria combined, with an estimated 60-80% of infections contracted from raw chicken. While most infections resolve without treatment, rising antimicrobial resistance means that some antibiotics are no longer effective, potentially leading to more serious illness.
Since the 1960s, global chicken numbers have increased seven-fold to approximately 27 billion, representing about 70% of all bird biomass on Earth. This industrialization has made animal protein affordable but also created new health risks. The study identified genetic changes in Campylobacter linked to adaptation to the chicken environment, including genes for antimicrobial resistance and survival in densely packed production systems where antibiotics are often used.