Scientists are still trying to determine the origin of the coronavirus, but the predominant theory is that it began in a food market in Wuhan, China.
So-called "wet markets" — usually a jumble of stalls carrying produce, seafood, some farmed meat — are found across China, as well as in many other parts of the world. The problem is that these wet markets sometimes also carry live animals — occasionally including illegal, sometimes exotic, wildlife — bought and slaughtered on the spot, increasing chances for the spread of disease.
A growing number of advocacy groups, politicians and other officials are calling to ban these types of markets worldwide. But enforcing such a ban would be a challenge.
Jan Vertefeuille, a senior advisor for advocacy at the World Wildlife Fund, one of the groups supporting a ban, says the animals in wet markets tend to be crammed into unsanitary cages, stacked on top of each other.
"You might have bats sitting on top of pigs, sitting on top of pangolins, sitting on top of civet cats, and all their bodily fluids are kind of flowing into each other," she says.
The animals are under chronic stress, she says, which weakens their immune systems. Viruses they carry can mingle and spread among species, including, occasionally, to humans.
"It's the perfect recipe for an epidemic, something like COVID-19 to emerge from a market like that," Vertefeuille says.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and the top U.S. infectious disease expert, has also expressed support for shutting wet markets.
"It boggles my mind how, when we have so many diseases that emanate out of that unusual human-animal interface, that we don't just shut it down," Fauci told "Fox & Friends" earlier this month.
In February, after the coronavirus outbreak, China's government banned selling wild animals at the wet markets. It did the same thing after the 2003 SARS outbreak, but that ban was lifted after about three months.
Republican Rep. Michael McCaul of Texas is among a bipartisan group of more than 60 members of Congress calling on international bodies including the World Health Organization to shut down live wildlife markets.
"We didn't learn the lessons from the past," he says. "And I think that's what we want to be looking at now, is how can we stop this from happening ever again?"
The question is whether such a ban is enforceable.
Much of the trade in wild animals is already illegal in China, but still widespread.
Certainly the WHO, a unit of the United Nations, doesn't have enforcement power. All it can do is offer guidance. It says that wet markets are an important source of food and jobs for people all over the world, but that governments should ensure food safety and "rigorously enforce bans on the sale of wildlife."