‘Human viruses often spread to animals’

HUMANS pass on more viruses to domestic and wild animals than they catch from them, a new study suggests.

University College London (UCL) researchers analysed all publicly available viral genome sequences, to see where viruses have jumped from one host to infect another vertebrate species – animals with a backbone and skeleton.

Most infectious diseases are caused by viruses circulating in animals, and when these cross over into humans they can cause disease outbreaks, epidemics and pandemics.

Humans have generally been considered as a sink for viruses rather than a source, with humanto-animal transmission of viruses receiving far less attention.

In the new study, scientists found that roughly twice as many host jumps were inferred to be from humans to other animals rather than the other way round. They also found even more animal-to-animal host jumps that did not involve humans.

According to the scientists, their findings highlight the underappreciated fact that human viruses often spread from humans into wild and domestic animals.

Understanding how and why viruses evolve to jump into different hosts may help experts figure out how new viral diseases emerge.

Study co-author Professor Francois Balloux, UCL Genetics Institute, said: “We should consider humans just as one node in a vast network of hosts endlessly exchanging pathogens.

“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 of novel illnesses, while also aiding conservation efforts.”

Lead author, PhD student Cedric Tan, UCL Genetics Institute and Francis Crick Institute, said: “When animals catch viruses from humans, this can not only harm the animal and potentially pose a conservation threat to the species, but it may also cause new problems for humans by impacting food security if large numbers of livestock need to be culled to prevent an epidemic, as has been happening with the H5N1 bird flu strain.

“Additionally, 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.” The findings are in Nature Ecology and Evolution.