09.04.2020 |

Human impact on wildlife increases risk of virus spillover, study

There must have been close contact with humans (Photo: S. Hermann & F. Richter, CC0)

Human impact on wildlife through activities such as hunting, farming and the destruction of habitats has increased the risk of viruses spilling over from animals to humans, new research shows. According to a study published in the journal Proceedings of the Royal Society on April 8, there is a link between environmental change and the transmission of animal viruses to humans: “Exploitation of wildlife through hunting and trade facilitates close contact between wildlife and humans, and our findings provide further evidence that exploitation, as well as anthropogenic activities that have caused losses in wildlife habitat quality, have increased opportunities for animal-human interactions and facilitated zoonotic disease transmission,” the authors write in the abstract of the study. “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. “The consequence is they’re sharing their viruses with us. These actions simultaneously threaten species survival and increase the risk of spillover,” she added.

For the study, the scientists assembled a large dataset of the 142 known viruses that are transmitted from animals to humans and the species that are involved as potential hosts. They used the Red List of Threatened Species, compiled by the International Union for Conservation of Nature (IUCN), and examined patterns in those species’ abundance, extinction risks and underlying causes for species declines. The researchers found that the top 10 mammalian species with the highest number of viruses shared with humans included eight domesticated species: pigs, cattle, horses, sheep, dogs, goats, cats and camels. This is likely a result of our frequent close interactions with these species for centuries. Wild animals that have increased in abundance and adapted well to human-dominated environments also share more viruses with people. This group includes, for example, some rodent, bat and primate species which live among people, close to human settlements and near farms and fields, making them high-risk for ongoing transmission of viruses to people. Bats have often been implicated as a source of “high consequence” pathogens, such as SARS.

At the other end of the spectrum are threatened and endangered species, the study notes. This includes animals whose population declines were connected to hunting, wildlife trade and decreases in habitat quality. These species “were also predicted to host nearly twice as many zoonotic viruses compared to threatened species declining for other reasons,” the authors write. “Anthropogenic activities that have altered the landscape, such as forest fragmentation, development and conversion to cropland, have caused declines in wildlife habitat quality, and, as with exploitation, are likely to also increase the probability of animal-human interactions during and subsequent to land conversion activities.” The scientists warn that human encroachment into biodiverse areas increases the risk of spillover of novel infectious diseases by enabling new contacts between humans and wildlife. “We need to be really attentive to how we interact with wildlife and the activities that bring humans and wildlife together,” Johnson said. “We obviously don’t want pandemics of this scale. We need to find ways to co-exist safely with wildlife, as they have no shortages of viruses to give us.” (ab)

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