The new coronavirus, which is infecting more and more people, has probably emerged among live animals in a market in Wuhan, a city in eastern China with more inhabitants than Sweden. In the animal markets, widely different species live closer to each other than they ever do in the wild. And the animals are stressed, which increases the risk of infections.

"It's like a crucible for viruses," says Björn Olsen, professor of infectious diseases at Uppsala University.

Animal viruses cause outbreaks

He has extensive experience in research on how viruses move between different species. These types of cross-border infections - so-called zoonoses - have caused many serious outbreaks of infectious diseases in humans.

Within the coronavirus group there are three known cases. In 2003, Sars originated in southern China. A similar infection, Mers, began to spread on the Arabian Peninsula in 2012. And three weeks ago, the first reports of yet another new variant of coronavirus came out in humans.

Common to those who first fell ill was that they had visited a now closed market in Wuhan where wild-caught animals were sold live as food.

Food culture threatens diversity

The trade in live animals is widespread and deeply rooted in the region's food culture. Besides bedding for zoonoses, it is a threat to biodiversity, according to Björn Olsen. He thinks it's time to close the animal markets.

- This might have been sustainable when there were few people on earth and hardly any transport. Now we are approaching eight billion and can move anywhere within a day. When reality changes, you have to adapt old traditions to new circumstances, says Björn Olsen.