This sexually transmitted disease (STD), which in its late stages can cause mental disorders, blindness, and death, is caused by a corkscrew-shaped bacterium called Treponema pallidum.

Syphilis, which swept through Europe in a devastating epidemic during the late 15th century, is now readily treated with antibiotics.

Syphilis, which is known as the great imitator because it mimics so many other diseases, is making its strongest comeback in 40 years in the U.S.. The surging number of cases...