The chickens were already getting sick when Yoshihiro Kawaoka arrived in the U.S. in August 1983. A few months before, in April, a bird flu virus had arisen in the poultry farms of eastern Pennsylvania, but veterinarians had deemed it to be “low pathogenic”—meaning it made chickens sick but did not kill many of them. As the virus swept through the poultry farms, however, a new strain developed. Chickens began to die in large numbers, and farmers started to fear for their livelihoods. The state called in the U.S. Department of Agriculture, which set up a temporary command and control center in a strip mall outside of Lancaster. To contain the epidemic, it culled 17 million birds from Pennsylvania down through Virginia.