This story was originally This was originally published in the Guardian and is part of the Climate Desk collaboration.
Urban ducks and crows may help us connect with nature, but scientists have found that wild birds that live near humans are more likely to harbor bacteria that are resistant to important antibiotics.
Antimicrobial resistance (AMR) is primarily caused by the overuse of medicines such as antibiotics by humans and livestock.
This issue is of serious concern: in 2019, there were approximately 4.95 million bacterial AMR-related deaths worldwide, of which 1.27 million were directly attributable to antimicrobial resistance.
The researchers say wild bird species that tend to appear in urban areas are breeding grounds for bacteria that are resistant to many drugs.
“Essentially what we’re looking at are genes that confer resistance to antibiotics used to treat human infections,” said study co-author Samuel Shepherd, from the INEOS Oxford Institute of Antibacterial Research.
The team said the finding is significant because wild birds have the ability to travel great distances, and Shepherd said a major concern is that these birds could transmit antibiotic-resistant bacteria to captive birds destined for human consumption, such as those kept on poultry farms.
Shepherd and his colleagues report their method in the journal Current Biology, analysing the genomes of bacteria found in 700 bird droppings samples from 30 wild bird species from Canada, Finland, Italy, Lithuania, Japan, Sweden, the UK and the US.
The research team particularly noted the presence of different strains. Campylobacter jejuni—A type of bacteria that is ubiquitous in birds as a natural part of their gut flora. Such bacteria are a major cause of gastroenteritis in humans, but antibiotics are typically only used in severe cases.
Shepherd added that wild birds are generally expected to carry one type of the virus each. C. jejuniwhich is specific to the species.
However, the research team found that wild birds that appear in urban areas have many more lineages. C. jejuni than animals that live away from humans.
Moreover, strains found in urban species contained roughly three times as many genes known to cause antimicrobial resistance, and these genes are also associated with resistance to a broader range of antimicrobials.
The authors suggest that wild birds could pick up antibiotic-resistant bacteria in a variety of ways: seagulls and crows, for example, are known to lurk in landfills, while ducks and geese could pick up antibiotic-resistant bacteria in rivers and lakes polluted by human wastewater.
Thomas van Bekker, an antibiotic resistance expert at ETH Zurich who was not involved in the study, said the research was unusual because it focused on the impact of human antibiotic use on animals.
“What are the consequences for the birds? We don’t know for sure, but it looks like we humans are to blame for this change,” he said.
Dana Gifford, from the University of Manchester, added that the findings could have implications for human health.
“Though alarming, the risk of direct transmission of resistance from urban birds to humans is unknown, although transmission from poultry to humans is well documented,” she said. “Urban development is encroaching on agricultural land, increasing contact between urban birds and poultry, raising great concern about indirect transmission through the food chain.”
Andrew Singer, from the UK Centre for Ecology and Hydrology, said more samples were needed to be sure the results were correct, but that precautions could be taken.
“The first thing we need to do is stop birds congregating around landfills, sewage treatment plants and animal waste piles, which are rich in pathogens and drug-resistant bacteria,” he said. “We also need to stop discharging untreated sewage into rivers, which exposes all the wildlife – and people – who use the rivers to human-associated pathogens and drug-resistant bacteria.”
