Early last spring, as cities worldwide were shutting down to halt the spread of COVID-19, Demaneuf, 52, began reading up on the origins of SARS-CoV-2, the virus that causes the disease. The prevailing theory was that it had jumped from bats to some other species before making the leap to humans at a market in China, where some of the earliest cases appeared in late 2019. The Huanan wholesale market, in the city of Wuhan, is a complex of markets selling seafood, meat, fruit, and vegetables. A handful of vendors sold live wild animals—a possible source of the virus.