Humans often spread viruses to wild and domestic animals, increasing their risk of disease, according to a study that challenges the long-held theory that humans are a reservoir of viruses.
Humans have never been considered the source of the virus, and human-to-animal transmission of viruses has received much less attention, an analysis of viral genomes by researchers at University College London has revealed.
“When animals catch viruses from humans, it can not only harm the animal and potentially pose a threat to the conservation of the species, but it can also create new problems for humans by affecting food security if large numbers of livestock have to be culled to prevent an epidemic, as has happened in recent years with the H5N1 bird flu strain,” said lead author Cedric Tan, a PhD student at UCL’s Genetics Institute and the Francis Crick Institute.
“Furthermore, if a human-borne virus infects a new animal species, the virus may continue to thrive even after being eradicated among humans, or even develop new adaptations before it ends up infecting humans again.
“Understanding how and why viruses evolve to jump to different hosts across the broader tree of life can help us understand how new viral diseases emerge in humans and animals,” Tan said.
For the study, published in the journal Nature Ecology and Evolution, the team used methodological tools to analyze nearly 12 million viral genomes.
They also used the data to reconstruct the evolutionary history and past host jumps of viruses across 32 viral families to look for mutations acquired by viral genomes during host jumps.
The researchers found that “roughly twice as many host jumps were derived from humans to other animals (known as anthroponosis) rather than the other way around.
This pattern was consistent across most virus families considered. In addition, they discovered even more jumps between animal and host that did not involve humans.”
“We should think of humans as one node in a vast network of hosts endlessly exchanging pathogens, rather than a sink for zoonotic bugs,” said co-author Professor Francois Balloux of the UCL Genetics Institute.
