A significant proportion of rats living in the New York municipal sewer systems are infected with SARS-CoV-2, a study carried out by researchers at the University of Missouri has found.


The team carried out two trapping sessions in the autumn of 2021 to round up wild Norway rats, Rattus norvegicus, in areas surrounding wastewater systems in city parks within Brooklyn. Of the 79 rats they captured, 13 tested positive for COVID – that's around 16 per cent.

In a separate experiment carried out within the laboratory, the researchers also found that coronavirus variants carried by humans, namely Alpha, Delta and Omicron, can cause infections in Sprague Dawley rats, a breed of albino rat commonly used in medical research.

After infection, they found high levels of the viruses in the animals’ upper and lower respiratory tracts. However, it's not yet clear if the rats are spreading the disease to humans.

“To the best of our knowledge, this is one of the first studies to show SARS-CoV-2 variants can cause infections in the wild rat populations in a major US urban area,” said Prof Henry Wan, director of the Center for Influenza and Emerging Infectious Diseases at the University of Missouri.

“Overall, our work in this space shows that animals can play a role in pandemics that impact humans, and it’s important that we continue to increase our understanding so we can protect both human and animal health.”

Rats are a common site in many urban areas across the world, New York City is home to around 8 million, meaning they frequently come into contact with humans. Further studies are essential to investigate how rats infect one another and how they could help to spread the virus amongst humans, the researchers say.

“Our findings highlight the need for further monitoring of SARS-CoV-2 in rat populations to determine if the virus is circulating in the animals and evolving into new strains that could pose a risk to humans,” said Prof Wan.

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.