Intensive chicken farming practices may be inadvertently fostering the growth and spread of Campylobacter bacteria, a pathogen linked to food poisoning and potentially contributing to the development of bowel cancer, according to new research from the University of Oxford. The study, published in the Proceedings of the National Academy of Sciences, suggests 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, with around 100 deaths attributed to infection each year. Government figures show a roughly one-third increase in cases since 2016. While most infections resolve within a week, symptoms include diarrhea, vomiting, and abdominal pain, and in severe instances, particularly for individuals with weakened immune systems, it can lead to life-threatening sepsis.
Scientists hypothesize that the expansion of factory farms, which house billions of chickens globally, provides an environment conducive to the bacteria's proliferation. As more chickens are kept in close proximity, the bacteria have increased opportunities to spread between birds, exchange genetic material, and evolve. Researchers analyzed 2,747 samples from chickens and wild birds across 30 countries over 45 years. Their findings indicate that Campylobacter has adapted to thrive in commercial poultry flocks, exhibiting traits such as antimicrobial resistance, which can complicate treatment.
This evolution may also make the bacteria more capable of causing severe human illness. Previous studies have also suggested a link between Campylobacter and cancer. Research published in Cell Host and Microbe indicated that the bacteria can release a toxin that may promote the aggressiveness and spread of existing bowel cancer cells by activating specific signals within them.
The Oxford researchers suggest that commercial chicken farms can act as reservoirs for these harmful bacteria. The global chicken population has grown significantly, with an estimated 31 billion birds worldwide. In England alone, there are close to 100 million broiler chickens raised for meat production. This dense population density, coupled with the potential introduction of bacteria from wild bird populations, creates an environment where Campylobacter can rapidly spread and establish itself within flocks.
"Industrial farming has created one of the largest animal habitats on the planet," said Sam Sheppard, professor of microbial genomics and evolution at the University of Oxford and senior author of the paper. "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."
Understanding the evolutionary consequences of these farming practices is considered crucial for mitigating future risks associated with zoonotic diseases and antimicrobial resistance. Earlier research from Oxford indicated that approximately 80 percent of human Campylobacter infections in Oxfordshire were linked to poultry meat, with many of these strains demonstrating antibiotic resistance.