Time and proximity are the biggest risks for wildlife disease spillover, a new study finds. The longer a species has been traded, the greater the chance its germs will jump over to humans. The researchers even quantified the risk: for every decade a species is traded, it shares an average of one more pathogen with humans.
In a new study published in Science, researchers analyzed 40 years of wildlife trade and animal-to-human disease transmission. They found that 41% of traded mammals share a pathogen with humans compared to just 6% of non-traded species, showing that trade is likely a driver of pathogen transmission.
“We have spent the last few years building this huge atlas of every virus that we know about,” said Colin Carlson, a disease ecologist at Yale University and co-author on the paper, in an interview with NPR. “When we see one of those viruses move from animals to humans, that’s a sure sign that something has happened.”
The researchers also found that species usually sold alive at markets, rather than dead, shared more viruses. And illegally traded species like primates and pangolins have higher amounts of pathogen transmission.
Carlson said that spending time in close contact with animals for years at a time “ensures” that humans will be exposed to their germs. But safeguards like using personal protective equipment, regulations and decreasing the demand for exotic animals can help stop disease before it spreads.
