Wildlife trade, habitat degradation driving virus spillover: Study

Exploitation of wildlife by humans through hunting, trade, and habitat degradation leads to close contact between the animals and humans, increasing the risk of spillover of viruses like the novel coronavirus which causes COVID-19, according to a study.

The study, published in the journal Proceedings of the Royal Society B, provides new evidence for assessing spillover risk in animal species and highlights how the processes that create wildlife population declines also enable the transmission of animal viruses to humans.

"Spillover of viruses from animals is a direct result of our actions involving wildlife and their habitat," said lead author Christine Kreuder Johnson, from the University of California, Davis in the US.

"The consequence is they're sharing their viruses with us. These actions simultaneously threaten species survival and increase the risk of spillover. In an unfortunate convergence of many factors, this brings about the kind of mess we're in now," Johnson said.

The scientists assembled a large dataset of the 142 known viruses that spill over from animals to humans and the species that have been implicated as potential hosts.

Using the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, they examined patterns in those species' abundance, extinction risks and underlying causes for species declines.

The data show clear trends in spillover risk that highlight how people have interacted with animals throughout history, the researchers said.

They found that domesticated animals, including livestock, have shared the highest number of viruses with humans, with eight times more zoonotic viruses compared to wild mammalian species.

This is likely a result of our frequent close interactions with these species for centuries, the researchers said.

According to the study, wild animals that have increased in abundance and adapted well to human-dominated environments also share more viruses with people.

These include some rodent, bat and primate species that live among people, near our homes, and around our farms and crops, making them high-risk for ongoing transmission of viruses to people, it found.

The researchers noted that at the other end of the spectrum are threatened and endangered species.

These are animals whose population declines were connected to hunting, wildlife trade and decreases in habitat quality, the said.

These species were predicted to host twice as many zoonotic viruses compared to threatened species that had populations decreasing for other reasons, according to the researchers.

Threatened and endangered species also tend to be highly managed and directly monitored by humans trying to bring about their population recovery, which also puts them into greater contact with people, they said.

Bats repeatedly have been implicated as a source of "high consequence" pathogens, including SARS, Nipah virus, Marburg virus and ebolaviruses, the study noted.