• Posted March 27, 2024

Animals Catch More Viruses From Us Than We Do From Them

People worry about deadly viruses leaping from animals into humans, but a new study suggests that wildlife is more at risk than humans are.

Roughly twice as many viruses pass from humans to animals than the other way around, researchers report March 25 in the journal Nature Ecology & Evolution.

“We should consider humans just as one node in a vast network of hosts endlessly exchanging pathogens,” said researcher Francois Balloux, chair of computational biology systems with University College London's Genetics Institute.

For the study, researchers analyzed nearly 12 million viral genomes that have been mapped and stored on public databases. With that data, they reconstructed the evolutionary histories and species jumps of 32 different viral families.

On average, viral host jumps are associated with an increase in virus mutations, reflecting how the germs must adapt to better spread among their new hosts.

Until now, concern has mostly revolved around viruses like Ebola, flu and COVID-19 that have passed into humans from animal carriers.

More than six out of every 10 known infectious diseases in people can be spread from animals, and three out of every four new or emerging infectious diseases in people come from animals, according to the U.S. Centers for Disease Control and Prevention.

But these results show that, to be prepared for the next pandemic, humans need to be just as concerned with the germs they spread to animals, researchers said.

“By surveying and monitoring transmission of viruses between animals and humans, in either direction, we can better understand viral evolution and hopefully be more prepared for future outbreaks and epidemics of novel illnesses,” Balloux said in a university news release.

Viruses that jump from humans into animals not only can potentially wipe out those species, but they also can affect food supplies for humans, noted lead researcher Cedric Tan, a doctoral student with the UCL Genetics Institute.

For example, tens of millions of chickens have had to be culled on farms to prevent the spread of a deadly strain of H5N1 bird flu, Tan noted.

There's also a risk that viruses that pass from humans into animals might return to the human race after developing even more deadly mutations, Tan said.

“If a virus carried by humans infects a new animal species, the virus might continue to thrive even if eradicated among humans, or even evolve new adaptations before it winds up infecting humans again,” Tan explained.

“Understanding how and why viruses evolve to jump into different hosts across the wider tree of life may help us figure out how new viral diseases emerge in humans and animals,” Tan concluded.

More information

The U.S. Centers for Disease Control and Prevention has more about diseases that spread between people and animals.

SOURCE: University College London, news release, March 25, 2024