Industrial poultry farming accelerating spread of food poisoning disease

Industrial poultry farming has led to a more than 100-fold increase in the movement of bacteria that cause food poisoning, scientists have found.

Campylobacter is the most common bacterial cause of diarrhoea worldwide, with people often falling ill after eating undercooked chicken or untreated water.

It is responsible for more than 3.5 times as many stomach flu cases in the UK each year as all other monitored foodborne bacteria combined.

The huge global expansion of chicken farming over the last few decades has created ideal conditions for the bacterium to spread, mix and acquire new traits that help it to survive, according to a study by Ineos Oxford Institute researchers at the University of Oxford published on Monday.

They said that since the 1960s, global chicken numbers have increased seven-fold to approximately 31 billion birds, with chickens now accounting for around 70% of all bird biomass on earth.

While the increase has allowed for the production of affordable animal protein at scale, the researchers said it has also allowed bacteria strains that once circulated in wild birds to mix extensively in commercial poultry populations, the experts said.

It comes after they analysed nearly 2,800 bacterial genomes collected from chickens and wild birds in 30 countries, including the UK and USA, between 1979 and 2024.

Using genomic analyses, the researchers identified genetic changes in campylobacter that were associated with adaptation to the chicken environment.

These included genes involved in antimicrobial resistance, which occurs when bacteria resist drugs designed to kill them, as well as traits that can help bacteria survive and thrive in modern poultry production systems.

The rising rates of antimicrobial resistance are also making campylobacter infections increasingly difficult to treat, the experts said.

Sam Sheppard, professor of microbial genomics and evolution at the University of Oxford and senior author of the paper, said: “Our findings provide new evidence that human-driven environmental change can increase the spread of infectious diseases.

“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”.

This means they are absorbing and amplifying bacterial strains from multiple sources.

As part of the research, mathematical modelling 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 Ineos Oxford Institute study found that 80% of human campylobacter infections in Oxfordshire are associated with poultry meat, and that many of these infections are resistant to antibiotics.

Oakem Kyne, a researcher at the University of Oxford and first author of the paper, 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.

“Understanding how farming practices influence bacterial evolution is an important step towards reducing the burden of foodborne disease.”