Leprosy is an ages-old disease, described in many historical texts. Mentioned in the Bible, leprosy was introduced in Europe in the 400s B.C., probably by the troops of the Persian ruler Xerxes (c. 519–465 B.C.) as they moved westward. By the twelfth century leprosy had reached epidemic proportions in western Europe, even claiming the lives of rulers (Portugal’s Alfonso II died from it in 1223, and Robert I, King of Scots, in 1329). Explorers and settlers from the European continent later carried the infectious chronic skin disease to the New World, where it was previously unknown.

The cause of leprosy was unknown. While some theorized it was contagious, others asserted that it was hereditary or was caused by eating certain foods (even potatoes were at one time blamed for originating the affliction). The disease gradually disappeared from Europe, attributable to improved living conditions, better nutrition, and, later, the advent of drugs that are effective in treatment.

The first clinical description was not made until 1874 when Norwegian physician Gerhard Henrik Hansen (1841–1912) discovered the leprosy bacterium. Since then the disease has also been called Hansen’s disease. Today, leprosy afflicts about 5 million people worldwide. It is endemic (native) to tropical or subtropical regions, including Africa, Central and South America, India, and Southeast Asia. Most cases of leprosy that occur in the United States are among immigrants from areas where the disease is endemic. Beginning in the mid-1950s, the Roman Catholic nun Mother Teresa (1910–1997) of Calcutta ministered to those afflicted with leprosy, setting up colonies for their care.