Genome study links industrial chicken farming to faster Campylobacter evolution

Researchers link industrial chicken farming to faster Campylobacter evolution, genome study tracks strain mixing between wild birds and poultry, antibiotic resistance traits rise alongside global chicken boom

A dataset of nearly 2,800 Campylobacter genomes collected from chickens and wild birds across 30 countries suggests that modern poultry production is accelerating the mixing and spread of the world’s most common bacterial cause of diarrhoea. According to The Guardian, the study spans samples gathered between 1979 and 2024 and was published in Proceedings of the National Academy of Sciences, with University of Oxford researcher Sam Sheppard listed as senior author.

Campylobacter is a familiar pathogen in rich countries because it rides on a familiar product: raw chicken. The Guardian reports that an estimated 60–80% of human Campylobacter infections are caught from raw chicken, not because cooking fails but because kitchens leak bacteria through splashes, hands, chopping boards and knives. In the UK, Campylobacter causes more than three times as many gastroenteritis cases each year as all other monitored foodborne bacteria combined, and while most patients recover without treatment, some require antibiotics and face elevated risk of longer-term complications such as irritable bowel syndrome.

What is new in the paper is the evolutionary map, reconstructed from genomes rather than from outbreaks and food-safety audits. The researchers report a sharp rise in the exchange of Campylobacter strains between wild birds and chickens as farming has intensified, allowing bacteria to mix, spread and pick up new traits. Before chicken domestication thousands of years ago, the study suggests strains were more tightly associated with particular bird species, with limited cross-infection. Since 1900, the authors estimate a roughly 100-fold increase in transitions between chickens and wild birds compared with pre-domestication, with the steepest growth in recent decades.

The scale of the host matters. The Guardian notes that global chicken numbers have risen seven-fold since the 1960s to about 27 billion birds, and that chickens now account for around 70% of all bird biomass on Earth. Industrial breeding has also compressed the production cycle: modern chickens reach adult size and are slaughtered at around five weeks old. A pathogen that can circulate through dense flocks, jump into wild birds and back again, and repeatedly encounter antibiotics used in animal production and human medicine gets far more evolutionary “rolls of the dice” than it did in smaller, slower systems.

The study’s warning is not that chicken has suddenly become unsafe, but that treatment options can quietly shrink. The Guardian reports that antimicrobial resistance traits have increased in circulating Campylobacter strains, and that some antibiotics previously used against serious infections are no longer effective. Food systems built to deliver cheap protein at scale can also build a high-throughput environment for bacterial adaptation, leaving households to manage the risk one cutting board at a time.

The genomes in this study were collected over decades, but the production curve they sit on is still rising. The world now keeps tens of billions of chickens, and Campylobacter has learned to travel with them.