Bruce is noted for his work in parasitology, especially for his discovery of the cause of brucellosis and sleeping sickness. Born in Melbourne, Australia, to Scottish immigrants, Bruce and his parents returned to Scotland when he was five years old. Although Bruce longed to become a professional athlete, he was stricken with pneumonia at age 17. Bruce studied natural history and medicine at the University of Edinburgh, and after graduation, he found a job working with a doctor. He later met Mary Elizabeth Steele, whom he married in 1883. The couple subsequently began a lifelong partnership in medical science.

After joining the Army Medical Service, David and Mary Bruce were assigned to Malta in 1884, where Bruce began a study of an often-fatal disease suffered by English soldiers assigned to the Maltese garrison. The disease, known as Malta, Mediterranean, or undulating fever, caused chills, sweats, and weakness. Using a microscope, Bruce...