Fascinating classics written long ago that are still good reading:
Defoe, Daniel. Journal of the Plague Year. New York: New American Library, 1960. (Original edition 1723.)
Although a work of fiction, the author lived in times when the bubonic plague was still around.
Nightingale, Florence. Notes on Nursing: What It Is and What It Is Not. New York: Dover Publications, 1969. (Original edition 1859.)
For a nice little old lady, Florence Nightingale was amazingly blunt and opinionated. She made generals tremble in their shoes. She would have made Hillary Clinton wilt!
Most important modern works:
Ewald, Paul W. Evolution of Infectious Disease. Oxford: Oxford University Press, 1994.
Seminal work on the evolution of infectious disease ...