Dozens of species that rarely, if ever, come in contact with one another in the wild fish, turtles, snakes, bamboo rats, bats, even foxes and wolf cubs are confined in close quarters, waiting to be butchered and sold. The animals are often stressed, dehydrated and shedding live viruses; the floors, stalls and tables are covered in blood, feces and other bodily fluids.

This is the scene at many of Chinas so-called wet markets, where a poorly regulated wildlife trade thrives and creates conditions that experts say are ideal for spawning new diseases.

You could not design a better way of creating pandemics, said Joe Walston, head of global conservation at the nonprofit Wildlife Conservation Society. Its really the perfect mechanism, not just for the Wuhan coronavirus but for the next ones that will undoubtedly emerge sooner rather than later.

The Huanan seafood market in Wuhan, a city of 11 million people in central China, is the suspected source of the current outbreak of a novel coronavirus that so far has killed 811 people and infected more than 37,000. Although far less deadly than the flu, which kills up to 61,000 people in the U.S. alone each year, the new coronavirus is particularly concerning for scientists as it has not been previously seen in humans.

Like the 2002-03 outbreak of severe acute respiratory syndrome, or SARS, in southern China that infected 8,098 people and killed 774 worldwide, the new coronavirus is believed to have originated in bats and jumped to humans through another species. Experts recently zeroed in on pangolins, endangered armadillo-like creatures and the worlds most poached and illegally trafficked mammals , as the possible intermediary host, as The Washington Post reported Friday. But independent scientists have questioned the research implicating pangolins.

Along with common domesticated animals and farm-raised species like ostriches and turtles, wet markets often process and sell rare, sometimes even imperiled, wildlife. Pangolin scales and other wild animal parts are used in traditional Chinese medicines, and the consumption of exotic species has become a status symbol in parts of mainland China all of which has helped fuel illegal hunting around the globe.

There are a number of endangered species that get mixed into these markets, said Peter Knights, the CEO of WildAid , a San Francisco-based organization working to end the illegal wildlife trade. One example is the yellow-breasted bunting , a critically endangered songbird and a delicacy in southern China.

The human health threat isnt so much subsistence hunting of wild animal meat or the presence of any single exotic species at markets, but rather commercialization of the wildlife trade, Knights said. Each new species brought into a crowded market represents another set of pathogens and viruses, increasing the risk of cross-species transmission. Making matters worse, he said, is deforestation, which exposes humans to new areas, the wildlife that lives there and the viruses the animals carry.

Youre inviting disaster, Knights said of mixing species in such large markets. Weve been lucky that we havent had more of these things.

Although the current focus is on China, similar live animal markets are also found in Southeast Asia and Africa. In Africa, cases of Ebola are associated with the hunting and processing of bush meat. And in the United States and other Western countries, food processing methods have resulted in numerous health issues, from cases of mad cow disease to outbreaks of E. coli and hepatitis A.