The Australia Animal Health Laboratory (AAHL) sits behind a large steel gate on a stretch of manicured grass, beside a pond, near the coast just outside downtown Geelong, which is 50 miles southwest of Melbourne. The gate opens to me at the behest of Emma Wilkins, a young communications officer, my contact. From outside, the building looks like a five-story warehouse of stony tan walls, with windows along the front and a tall water tower like a minaret rising out of its middle. AAHL is filled with special laboratories and expert researchers devoted to the study of animal diseases, including those diseases—known as zoonoses—caused by pathogens that pass sometimes from animals into humans. That category includes some of the most deadly viruses on the planet.

At Reception, I’m issued a necklace security badge, which I must use to scan-and-buzz myself, always with an escort, through each door. Upstairs I’m invited into the office of Dr. Linfa Wang, genial, youthful, casual in jeans and jacket—the eminent molecular virologist I’ve come to see. Wang is widely recognized for his work on bats as hosts for dangerous emerging viruses, virtually all of which are zoonotic. His most recent work has been on Hendra, a relatively obscure but lethal virus that kills horses and people in Australia, and on Nipah, a related virus that kills pigs and people in Malaysia and Bangladesh. During its first known spillover, in Malaysia, in 1998, Nipah killed 109 people, most of them pig farmers or abattoir workers, and resulted in the culling of 1.1 million pigs…