The novel coronavirus and the SARS outbreak of 2003 have two things in common: Both are from the coronavirus family, and both have been associated with animals commonly sold in "wet markets."

Historically at such markets, outdoor stalls are squeezed together to form narrow lanes, where locals and visitors shop for cuts of meat and ripe produce. A stall selling caged chickens may abut a butcher counter, where meat is chopped as nearby dogs watch hungrily. Some vendors hock hares, while seafood stalls display glistening fish and shrimp.

Wet markets put people and live and dead animals — dogs, chickens, pigs, snakes, civets, and more — in constant close contact. That makes it easy for zoonotic diseases to jump from animals to humans.

"Poorly regulated, live-animal markets mixed with illegal wildlife trade offer a unique opportunity for viruses to spill over from wildlife hosts into the human population," the Wildlife Conservation Society said in a statement.

In the case of SARS and the new coronavirus disease, called COVID-19, bats were the original hosts. The bats then infected other animals, which transmitted the disease to humans.

The market where the current outbreak may have started, the Huanan Seafood Wholesale Market in Wuhan, was shuttered January 1. Wuhan authorities banned the trade of live animals at all wet markets there soon after, and China announced a temporary national ban on the buying, selling, and transportation of wild animals in markets, restaurants, and online marketplaces across the country as well. However, research since then has indicated the market may not have been the origin of the outbreak.

That ban is now permanent. Farms that breed and transport wildlife to wet markets were also quarantined and shut down.

Here's what Chinese wet markets looked like over the years before these new policies went into effect.