Intensive farming techniques have led to a common antibiotic-resistant pathogen to become capable of infecting both cattle and humans, according to a study which suggests the need to check agriculture practices for such outbreaks. The scientists, including those from the University of Sheffield in the UK, investigated the evolution of Campylobacter jejuni, a bacterium carried by chickens and cattle, and a leading cause of food poisoning.
Based on their findings, published in the journal PNAS, the researchers said the bacterium is able to infect more than one species because of its ability to transfer genes, and adapt quickly to new host environments.
They said overuse of antibiotics, high animal numbers, and low genetic diversity caused by intensive farming techniques increase the likelihood of these pathogens becoming a major public health risk.
These bacteria are often resistant to antibiotics, due to use of the drugs in farming, and can be transferred to people when they eat undercooked meat and poultry, the scientists said.
When they assessed the genetic evolution of the pathogen, the researchers 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 scientists suggest that changes in cattle diet, anatomy, and physiology triggered the transfer of genes between general and cattle-specific strains of the pathogen.
They noted that this helped the bacterium to cross the species barrier and infect humans, triggering a major public health problem.
"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," said Professor Dave Kelly, who led the study at the University of Sheffield.
Kelly said 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," he added.
According to study co-author Sam Sheppard from the University of Bath in the UK, cattle infected with the pathogen pose a major public health risk for humans.
"There are an estimated 1.5 billion cattle on Earth, each producing around 30 kilogrammes of manure each day. If roughly 20 per cent of these are carrying Campylobacter, that amounts to a huge potential public health risk," Sheppard said.
The scientists believe that the finding 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."