Chicken farming accelerating diarrhoea bacteria spread
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- The study, published in PNAS, analyzed nearly 2,800 bacterial genomes from chickens and wild birds across 30 countries between 1979 and 2024, reconstructing strain evolution and cross-species transmission rates.
- Global chicken populations have grown seven-fold since the 1960s to approximately 27 billion birds, now accounting for roughly 70% of all bird biomass on Earth—creating what researchers call a 'cauldron of bacterial evolution.'
- Campylobacter strain transitions between chickens and wild birds increased an estimated 100-fold since 1900 compared with pre-domestication, with the trend steepening sharply in recent decades as intensive breeding accelerated.
- Campylobacter is the most common bacterial cause of diarrhoea worldwide, causing more than three times as many gastroenteritis cases in the UK annually as all other monitored foodborne bacteria combined, with 60-80% of infections traced to raw chicken.
- Antimicrobial resistance traits are rising in circulating campylobacter strains, raising concern that antibiotics previously used to treat serious infections may no longer be effective.
- Prof Sam Sheppard of the University of Oxford warned that hybridising strains can produce 'new Frankenstein monster bugs' and argued the world 'can't continue to produce chickens at this huge capacity.'
- Maya Pardo of Communities Against Factory Farming criticised UK government plans to relax planning rules for new factory farms as 'absurd' given the mounting public-health evidence.
Why it matters: With campylobacter already driving three times more UK gastroenteritis cases than all other monitored foodborne bacteria combined and 60-80% of infections linked to raw chicken, rising antimicrobial resistance in circulating strains raises the stakes for routine infections that occasionally require antibiotics. The research lands just as UK policymakers weigh relaxing planning rules to permit more factory farms—a move critics argue ignores accelerating evidence of industrial-scale pathogen evolution.
