Industrial chicken farming spreading leading cause of food poisoning

By Stephen Beech

Industrial poultry farming is accelerating the spread of a leading cause of food poisoning, warns new research.

It has led to a more than 100-fold increase in the movement of Campylobacter — the leading bacterial cause of diarrhea worldwide, according to the University of Oxford study.

Industrial-scale chicken farming has allowed strains that once circulated in wild birds to mix extensively in commercial poultry populations, say scientists

Campylobacter is the most common bacterial cause of food poisoning around the world, causing more than 3.5 times as many gastroenteritis cases in the U.K. each year as all other monitored foodborne bacteria combined.

Experts say rising rates of antimicrobial resistance (AMR), which occurs when bacteria resist drugs designed to kill them, are making Campylobacter infections increasingly tough to treat.

Scientists from the Ineos Oxford Institute for antimicrobial research (IOI) analyzed more than 2,700 bacterial genomes collected from chickens and wild birds in 30 countries, including the U.K. and United States, between 1979 and 2024.

Their findings, published in the Proceedings of the National Academy of Sciences (PNAS), show that the huge global expansion of chicken farming has created ideal conditions for the bacterium to spread, mix and acquire new traits that help it survive.

Since the 1960s, global chicken numbers have increased sevenfold to about 31 billion birds.

Chickens account for about 70% of all bird biomass on Earth today.

While the increase in numbers has led to the production of affordable animal protein at scale, scientists say it has also created "ideal" conditions for bacteria to adapt and spread.

Using genomic analyses, the research team identified genetic changes in Campylobacter that were associated with adaptation to the chicken environment.

The changes included genes involved in antimicrobial resistance, oxidative stress tolerance, metal acquisition and motility, and traits that can help bacteria survive and thrive in modern poultry production systems.

Study senior author Sam Sheppard said: "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.

"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 these evolutionary consequences is essential if we are to reduce future risks from zoonotic disease and antimicrobial resistance."

The study also suggests that vast, densely populated chicken flocks may act as ecological "pathogen sponges" — absorbing and amplifying bacterial strains from multiple sources.

Mathematical modeling showed that once chicken populations reach a critical scale, strains originating in wild birds can become self-sustaining within poultry populations, even when poorly adapted to their new host.

A previous study from the IOI found that 80% of human Campylobacter infections in Oxfordshire are associated with poultry meat, and that many of these infections are resistant to antibiotics.

Study first author Oakem Kyne, a University of Oxford doctoral student, said: "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."

He added: "Understanding how farming practices influence bacterial evolution is an important step toward reducing the burden of foodborne disease."