Modern chicken farming may be allowing a dangerous bacteria linked to cancer and sepsis to thrive, scientists have warned.
Oxford University researchers have found a 100-fold increase in the spread of campylobacter among commercial chickens over the last 35 years.
Campylobacter in contaminated, uncooked poultry is the main cause of bacterial food poisoning in the UK, causing around 70,000 cases last year.
While most people will recover within a week, infection from the bacteria can also be deadly. It has even been linked to changes that fuel the spread of bowel cancer in some studies.
According to the Food Hygiene Certificate body, campylobacter infection is responsible for around 100 deaths every year in Britain.
Cases of the illness, which causes diarrhoea, vomiting and abdominal pain, have risen by roughly a third since 2016, Government figures show.
Now authors of the new study – published in the Proceedings of the National Academy of Sciences – say the expansion of factory farms may be allowing the bacteria to spread among chickens sold in supermarkets.
‘Our findings provide new evidence that human-driven environmental change can increase the spread of infectious diseases,’ they wrote.
Modern chicken farming may be allowing a dangerous bacteria linked to cancer and sepsis to thrive, scientists have warned
Campylobacter bacteria is typically spread to humans by eating undercooked poultry but it can also be transmitted through water and, in rare cases, from person to person.
Although it naturally circulates among wild birds, it is also found in commercial poultry.
The researchers said the world’s chicken population has grown seven-fold from the 1960s to around 31 billion birds.
With more chickens living in commercial flocks than ever before, the bacteria have more opportunities to pass between birds, exchange genes and evolve.
To investigate the bacteria’s evolution, researchers analysed 2,747 samples collected from chickens and wild birds in 30 countries over a 45-year period.
After studying its DNA, they found campylobacter has evolved in ways that make it better suited to surviving in commercial chicken flocks – sometimes called ‘factory farms’.
These include antimicrobial resistance – when bacteria develop the ability to survive antibiotics – which can make infections harder to treat.
They also say commercial chicken farms – of which there are more than 1,500 in Britain – may act like ‘sponges’ for harmful bacteria.
As thousands of birds are kept close together, bacteria from different sources – including wild birds – can enter chicken flocks, spread quickly and multiply.
Their computer models showed that once chicken populations become large enough, these bacteria continue circulating widely within flocks.
Sam Sheppard, professor of microbial genomics and evolution at the University of Oxford, and senior author of the paper, said: ‘Industrial farming has created one of the largest animal habitats on the planet.
Oxford University researchers have found a 100–fold increase in the movement of campylobacter bacteria between wild birds and commercial chickens since 1900
‘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 findings build on an earlier Oxford study, which found that around 80 per cent of human campylobacter infections in Oxfordshire were linked to poultry meat.
Many of those infections were also resistant to antibiotics.
Oakem Kyne, a student at the University of Oxford and first author of the paper, added: ‘As 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.’
In England alone, there are estimated to be close to 100 million broiler chickens – bred specifically for meat production.
Symptoms of campylobacter infection can include blood-stained diarrhoea, as well as stomach pains and vomiting.
In the most serious cases, particularly among people with weakened immune systems, the bacteria can enter the bloodstream and trigger life-threatening sepsis.
Separate studies have also suggested Campylobacter may affect some cancers.
One published last December in the journal Cell Host and Microbe found the bacteria may help existing bowel cancers become more aggressive and spread more easily.
The researchers, from China, said campylobacter releases a toxin that effectively ‘activates’ signals inside existing bowel cancer cells.
They believed that this made them invade nearby tissue and spread to other parts of the body.
