China's markets, where wild and often poached animals are packed together, have been described as a breeding ground for disease and an incubator for a multitude of viruses to evolve and jump the species barrier to humans.
More than 500 people have been infected by the new flu-like virus that authorities say emerged from illegally traded wildlife in a seafood market in the central Chinese city, with the death toll at 17 and expected to rise.
"The origin of the new coronavirus is the wildlife sold illegally in a Wuhan seafood market," Gao Fu, director of China Center for Disease Control and Prevention, told a briefing.
Preliminary research suggested that in the most recent stage of its evolution, the Wuhan virus was passed on to humans from snakes. But Chinese government medical adviser Zhong Nanshan has also identified badgers and rats as possible sources.
Conservationists and health experts have long denounced the trade in wildlife for its impact on biodiversity and the potential for spreading disease in markets.
"The animal welfare part of this is obvious, but much more hidden is this stashing and mixing of all these species together in a very small area, with secretions and urine mixed up together," said Christian Walzer, executive director of the New York-based Wildlife Conservation Society.
China's wet markets have already been blamed for outbreaks of other infectious diseases in China and southeast Asia, including the virus responsible for Severe Acute Respiratory Syndrome (SARS), which killed nearly 800 people worldwide in 2003.
"The other thing you have to consider is that these animals are massively stressed in these cages so their immune systems fail very quickly," said Walzer.
"It is a perfect system. You couldn't do it any better if you tried," Walzer said of the markets' propensity to generate viruses.
MARKET FORCES
Photographs taken at the Wuhan market before it was closed at the end of last year show cages packed with snakes, porcupines and foxes. Media said about 50 types of wild animal were on sale at the market, including endangered pangolins.
According to a report by the China Business Journal, a state-owned paper that interviewed the sister of a vendor infected by the virus, snakes, ducks and wild rabbits were popular at the market.
Since the outbreak began, authorities in Wuhan and elsewhere have shut down markets, zoos and forest parks, suspended trade in live poultry and the trade and transport of wild animals, though residents in some areas said the measures appeared to be largely symbolic.
The southeastern province of Guangdong, where a wide variety of animals are sold, has long been regarded as a prime source of new diseases.
Scientists believe SARS was caused by cross-species transmission in the province - with the blame initially falling on masked palm civets, which are considered a delicacy.
Authorities slaughtered thousands of the animals although bats were later believed to have been the source of SARS.
After SARS, China tried to improve the way the animal trade is regulated. At the same time, authorities have tried to curb the poaching of exotic species and has a long list of officially protected wildlife.
But efforts to protect animals often lose out to generations of tradition.
Environmentalists have long campaigned for new laws to restrict the use of wild animals in Chinese medicine and to develop synthetic alternatives.
But many animal products are still easily available.
Snakes, peacocks and even crocodiles are on sale via Taobao, a Chinese e-commerce website run by Alibaba.
Reuters contacted an Inner Mongolia resident named Gong Jian who sells snake, camel, crocodile and deer meat via WeChat.
Given booming business, he said he was aiming to expand his online marketing."Customers really like the crocodile - they stew it," he said.