Intensive Farming Increases Risk of Disease Spread to Humans

An international team of researchers led by the Universities of Bath and Sheffield, investigated the evolution of Campylobacter jejuni, a bacterium carried by cattle which is the leading cause of gastroenteritis in high-income countries.

Campylobacter jejuni under an electron microscope The researchers, publishing in the prestigious journal Proceedings of the National Academy of Sciences, studied the genetic evolution of the pathogen and found that cattle-specific strains of the bacterium emerged at the same time as a dramatic rise in cattle numbers in the 20th Century.

The authors of the study suggest that changes in cattle diet, anatomy and physiology triggered gene transfer between general and cattle-specific strains with significant gene gain and loss. This helped the bacterium to cross the species barrier and infect humans, triggering a major public health problem.

Combine this with the increased movement of animals globally, intensive farming practices have provided the perfect environment in which to spread globally through trade networks.

Professor Sam Sheppard Director of Bioinformatics from the Milner Centre for Evolution at the University of Bath, said: “There are an estimated 1.5 billion cattle on Earth, each producing around 30 kg of manure each day; if roughly 20 per cent of these are carrying Campylobacter, that amounts to a huge potential public health risk.

“Over the past few decades, there have been several viruses and pathogenic bacteria that have switched species from wild animals to humans: HIV started in monkeys; H5N1 came from birds; now Covid-19 is suspected to have come from bats.

“Our work shows that environmental change and increased contact with farm animals has caused bacterial infections to cross over to humans too.

“I think this is a wake-up call to be more responsible about farming methods, so we can reduce the risk of outbreaks of problematic pathogens in the future.”

Professor Dave Kelly from the Department of Molecular Biology and Biotechnology at the University of Sheffield said: “Human pathogens carried in animals are an increasing threat and our findings highlight how their adaptability can allow them to switch hosts and exploit intensive farming practices.”

The researchers hope that their study can help scientists predict potential problems in the future so they can be prevented before they turn into another epidemic.

Reference
Mourkas E, Taylor AJ, Méric G, Bayliss SC, Pascoe B, Mageiros L, Calland JK, Hitchings MD, Ridley A, Vidal A, Forbes KJ, Strachan NJC, Parker CT, Parkhill J, Jolley KA, Cody AJ, Maiden MCJ, Kelly DJ, Sheppard SK (2020) "Agricultural intensification and the evolution of host specialism in the enteric pathogen Campylobacter jejuni." is published in Proceedings of the National Academy of Sciences (USA) DOI: 10.1073/pnas.1917168117.

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