Overuse of antibiotics, high animal numbers and low genetic diversity caused by intensive farming techniques increase the likelihood of pathogens becoming a major public health risk, according to scientists at the University of Sheffield.
An international team of researchers led by the Universities of Sheffield and Bath investigated the evolution of Campylobacter jejuni, a bacterium carried by chickens and cattle which is the leading cause of gastroenteritis.
The bacteria are often resistant to antibiotics, due to use of the drugs in farming, and can be transferred to humans through eating undercooked meat and poultry.
The research, published in 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.
Professor Dave Kelly from the Department of Molecular Biology and Biotechnology, who led the study 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.
“Human activities have had a profound effect on the Earth’s ecosystems and biodiversity, particularly among livestock species, such as cattle. Escalating livestock numbers and global trade have been linked with the emergence of zoonotic diseases that pose a significant threat to both animal and human health, with the current Covid-19 pandemic being the most dramatic and serious example to date.”
Professor Sam Sheppard 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 30kg 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.
“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.”
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.