Animals sold in the wildlife trade are 50 per cent more likely to share at least one disease with humans, according to a landmark analysis of the spillover risks posed by the industry.

The research, published in Science journal on Thursday, examined over 2,000 traded mammal species and compared the data to international trade records and detailed pathogen databases.

It found 41 per cent of traded mammals shared at least one pathogen with humans, compared to 6.4 per cent of species that are not bred, transported, bought or sold. Overall, traded mammals are 1.5 times more likely than their counterparts to share pathogens with humans.

“It was surprising to find such a clear signal between this trade and the number of pathogens shared between [mammals and] humans,” said Dr Jérôme Gippet, a postdoctoral researcher at the University of Fribourg and lead author of the paper.

“It suggests that the trade is not just one of the things that promotes animal human pathogen transmission – but it’s one of the most important ones,” he told the Telegraph.

The connection between the wildlife trade and pathogen emergence is not new. The industry – which often sees a range of animals kept in cramped, unsanitary conditions – has been linked to a range of epidemics and pandemics.

The Sars outbreak in 2002-2003 was traced to the civet cat trade, and the Ebola outbreak in West Africa from 2014 was probably driven by bushmeat consumption or contact. While a World Health Organization committee has not excluded a laboratory leak, it also concluded last year that “weight of available evidence” suggests Covid-19 emerged after a zoonotic spillover.

But scientists not involved in the latest research said the Science paper is the most definitive attempt to quantify the spillover risk posed by both the legal and illegal wildlife trade.

“I’ve not seen this sort of analysis of the wildlife trade before… [but] it’s the scale of the analysis that gives it power,” said Prof Edward Holmes, an evolutionary biologist and virologist at the University of Sydney. “[This] serves as yet another reminder of how bad this trade is, from so many angles.”

The results also hone in on two particular threats: time and wet markets.

The 40-year analysis found that the threat of transmission increases over time, with mammal species sharing an extra pathogen with humans for every 10 years spent in the global trade.

The researchers also found that species traded alive were 34 per cent more likely to share pathogens with humans. Hunting, by contrast, showed negligible impact in driving spillover.

Dr Colin Carlson, an assistant professor of epidemiology at Yale University and a co-author of the paper, said the results corroborated some of his hypotheses, and challenged others.

“The wildlife trade is a much faster route of disease emergence than I thought it was,” he said. “One pathogen shared every decade is just so striking.”

Dr Carlson added that the paper is significant because it validates existing hypotheses explaining why the wildlife trade is a risk – from inter-species mixing to poor conditions – and shows these threats can be measured.

The next step is to use this data to better anticipate the risks, and to develop strategies to reduce spillover, especially surveillance and community education. The authors said the solution is unlikely to be a blanket shut down of the wildlife trade, which could drive the industry underground.

“Just because there’s a risk factor somewhere doesn’t mean it’s reversible,” said Dr Carlson. “So while we have really good evidence here that the wildlife trade as a general phenomenon is a risk for human health, that’s very different from evidence saying that banning the wildlife trade benefits human health.”

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