He immigrated to the United States in 1928, settling at first in Detroit, Michigan, and working for a time in the automobile industry.

[1] Following completion of his doctorate, Duffy joined the faculty at Northwestern State College of Louisiana initially teaching English and European history.

He finished his career as the Priscilla Alden Burke Professor of History at the University of Maryland, College Park, having an endowed professorship.

The book describes the impact of disease as a significant determinant of the colonization of North America, in addition to famine and war.

These included such subjects as: the history of medicine among Native Americans, public health for school children including the history of vaccination programs, the public health impact of cholera and smallpox epidemics, the personal and societal impacts of masturbation and clitoridectomy, and medical ethics.

[1] Duffy died at his home in Baton Rouge, Louisiana, on June 20, 1996, where he had been living for the last nine years of his life.