Intensive chicken farming practices may be contributing to a significant increase in Campylobacter bacteria, a pathogen linked to food poisoning, sepsis, and changes that fuel the spread of bowel cancer, according to new research from Oxford University. The study, published in the Proceedings of the National Academy of Sciences, found a 100-fold increase in the movement of this bacteria between wild birds and commercial chickens over recent decades.
Campylobacter is the leading cause of bacterial food poisoning in the UK, resulting in approximately 70,000 cases annually and around 100 deaths each year. Government figures indicate a roughly one-third rise in reported infections since 2016. While most infections resolve within a week, severe cases can lead to life-threatening sepsis, particularly in individuals with weakened immune systems. Emerging research has also suggested a potential link between Campylobacter and the aggressiveness of existing bowel cancers.
Scientists involved in the study believe that the expansion of factory farms, where vast numbers of chickens are housed closely together, provides an environment where Campylobacter can thrive and spread more easily. The global chicken population has grown substantially, increasing opportunities for the bacteria to transfer between birds, exchange genetic material, and evolve. Researchers analyzed nearly 3,000 samples from chickens and wild birds across 30 countries over 45 years. Their DNA analysis revealed that Campylobacter has adapted to better survive within commercial chicken flocks, exhibiting traits such as antimicrobial resistance, which can complicate treatment of infections.
"Our findings provide new evidence that human-driven environmental change can increase the spread of infectious diseases," the study authors wrote. They suggest that commercial chicken farms can act as reservoirs for harmful bacteria. Once large populations are established, these bacteria can circulate widely within flocks, gaining opportunities to spread and become entrenched.
Sam Sheppard, a professor at the University of Oxford and senior author of the paper, stated, "Industrial farming has created one of the largest animal habitats on the planet. 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 emphasized the importance of understanding these evolutionary consequences to mitigate future risks from zoonotic diseases and antimicrobial resistance.
This research builds on previous Oxford studies, which found that a significant percentage of human Campylobacter infections in the Oxfordshire region were linked to poultry meat, with many strains showing antibiotic resistance. Oakem Kyne, the paper's first author, noted that as bacterial strains adapt to poultry environments, they can acquire traits that enhance survival, including resistance to antibiotics, highlighting the importance of understanding how farming practices influence bacterial evolution to reduce the burden of foodborne diseases.
Campylobacter typically spreads to humans through the consumption of undercooked poultry, but can also be transmitted via contaminated water and, in rare instances, person-to-person contact. In England alone, there are an estimated close to 100 million broiler chickens raised for meat production annually.