This story originally appeared in The Guardian and is part of the Climate table collaboration.
Urban ducks and crows may offer us a connection to nature, but scientists have found that wild birds living close to humans are more likely to harbour bacteria resistant to important antibiotics.
Antimicrobial resistance (AMR) is largely caused by the overuse of drugs such as antibiotics in humans and livestock.
The issue is very worrying: According to 2019 dataAround 4.95 million deaths worldwide were associated with bacterial AMR, including 1.27 million directly caused by such resistance.
Researchers say wild bird species that tend to appear in urban environments are reservoirs of bacteria with resistance traits to a range of drugs.
“Basically, what we’re looking at are genes that confer resistance to antimicrobials that would be used to treat human infections,” said Samuel Sheppard, co-author of the research from the Ineos Oxford Institute for Antimicrobial Research.
The team says their findings are important because wild birds have the ability to travel considerable distances. Sheppard said a key concern was that these birds could transmit antimicrobial-resistant bacteria to captive birds intended for human consumption, such as those kept on poultry farms.
In a paper published in the journal Current Biology, Sheppard and colleagues report how they analyzed the genomes of bacteria found in 700 bird droppings samples from 30 wild bird species in Canada, Finland, Italy, Lithuania, Japan, Sweden, the United Kingdom and the United States.
The team specifically analyzed the presence of different strains of Campylobacter jejuni—a type of bacteria found everywhere in birds and a natural part of their gut microbiome. These bacteria are one of the main causes of human gastroenteritis, although antibiotics are generally only used in severe cases.
Sheppard added that, in general, each wild bird would be expected to harbour a single strain of C. jejunispecific to that species.
However, the team found that wild birds appearing in urban environments contain many more strains of C. jejuni than those who live far away from humans.
What’s more, strains found in urban-dwelling species contained about three times more genes known to result in antimicrobial resistance, genes that are also associated with resistance to a broader range of antimicrobials.
The authors suggest that wild birds can pick up antimicrobial-resistant bacteria in several ways: seagulls and crows, for example, are known to hang out in landfills, while ducks and geese can pick them up from rivers and lakes contaminated with human sewage.
Thomas Van Boeckel, an expert on antimicrobial resistance at ETH Zurich who was not involved in the work, said the research was unusual because it focused on the impact of antimicrobial use by humans on animals.
“What are the consequences of this for birds? We don’t know for sure, but it seems that humans are responsible for this change,” he said.
Danna Gifford, from the University of Manchester, added that the findings could have implications for human health.
“While alarming, the risk of direct transmission of resistance from urban birds to humans is unclear. However, transmission from poultry to humans is well documented,” she said. “With urban development encroaching on agricultural land, increased contact between urban birds and poultry raises significant concerns about indirect transmission through the food chain.”
Andrew Singer, from the UK’s Centre for Ecology and Hydrology, said more samples were needed to ensure the results were valid, but precautions could be taken.
“The most obvious starting point is to ensure that birds do not congregate at our landfills, wastewater treatment plants and animal manure piles, where both pathogens and AMR are abundant,” she said. “In addition, we must also eliminate the discharge of untreated sewage into our rivers, which exposes all the wildlife that use them (and humans) to human-associated pathogens and AMR.”
