Overuse of antibiotics, high number of animals and low genetic diversity caused by intensive farming techniques increase the likelihood that the pathogens will become a major public health risk, according to new research by British scientists .
An international team of researchers led by the universities of Bath and Sheffield has studied the evolution of Campylobacter jejuni, a bacteria carried by livestock that is the main cause of gastroenteritis in high-income countries.
Facts about Campylobacter:
- Causes bloody diarrhea in humans
- Transferred to humans after eating contaminated meat and poultry
- Although it is not as dangerous as typhoid, cholera or E. coli, it causes serious illness in patients with underlying health conditions and can cause lasting damage.
- About 1 in 7 people have an infection at some point in their life
- Causes three times as many cases as E. coli, Salmonella and listeria combined
- Transported in the feces of chickens, pigs, cattle and wild animals
- Campylobacter is estimated to be present in the faeces of 20% of cattle worldwide
- The bug is very resistant to antibiotics due to their use in agriculture
The researchers, published in the journal Proceedings of the National Academy of Sciences, studied the genetic evolution of the pathogen and found that specific strains of cattle from the bacteria appeared along with a dramatic increase in the number of cattle in the 20th century.
The study authors suggest that changes in cattle diet, anatomy and physiology triggered gene transfer between general and specific strains of cattle with significant gain and loss of genes. This helped the bacteria cross the species barrier and infect humans, triggering a major public health problem.
Combining this with the increased movement of animals around the world, intensive farming practices have provided the perfect environment in which to spread globally through trade networks.
Professor Sam Sheppard, of the Milner Center for Evolution at the University of Bath, said: “There are around 1.5 billion cattle on Earth, each producing around 30 kg of manure a day; if about 20% of between them carry Campylobacter, this represents a huge potential risk for public health.
“In recent decades, there have been several pathogenic viruses and bacteria that have passed species from wild animals to humans: HIV started in monkeys; H5N1 came from birds; now Covid-19 is suspected of ‘be from bats.’
“Our work shows that environmental changes and increased contact with farm animals have also caused bacterial infections.
“I think it’s a red flag to be more responsible about farming methods, so that we can reduce the risk of outbreaks of problematic pathogens in the future.”
Professor Dave Kelly of the Department of Molecular Biology and Biotechnology at the University of Sheffield said: “Human pathogens transported by animals are a growing threat and our results highlight how their adaptability can allow them to change hosts and to exploit intensive farming practices. “
The researchers hope their study will help scientists predict potential problems in the future so that they can be avoided before they turn into another epidemic.