Throughout history, battles and wars have been lost due to typhus epidemics that spread among soldiers fighting in unsanitary conditions. After World War I, 25 million people in the Soviet Union alone were infected with the disease. People forced to live in crowded, filthy, rodent-infested neighborhoods also suffered untimely deaths from the disease.

Howard Taylor Ricketts, an American pathologist born in Findlay, Ohio in 1871, is credited with discovering the genus Rickettsia, the cause of the disease, during his studies of Rocky Mountain spotted fever, which he noticed resembled typhus. In 1910, Ricketts traveled to Mexico City to study typhus, which he found was transmitted by a body louse. But his research had tragic results. Before he could return to the United States where he had accepted a position at the University of Pennsylvania, Ricketts died of typhus, the very disease he was studying.

At the same time, the curiosity of...