In an interview, Dr. Peter Piot recalled when he first saw the spindly virus under a microscope and reflected on a five-decade career spent fighting two deadly pathogens.

© Daniel Berehulak/The New York Times

In an interview, Dr. Peter Piot recalled when he first saw the spindly virus under a microscope and reflected on a five-decade career spent fighting two deadly pathogens.

© Daniel Berehulak/The New York Times