7. With a mortality rate in excess of 50 percent if left untreated, after a period of decline in late late-20th century millions of new cases of syphilis are now being diagnosed each year
Most commonly spread by sexual activity, although also transmittable during pregnancy to an unborn infant, syphilis is a four-stage infection-causing tremendous medical complications in those afflicted. Beginning with sores and rashes, including on the genitalia, the infection develops slowly until, after three to fifteen years, if left untreated syphilis begins to attack the brain and other vital organs. The precise origin of syphilis is uncertain, with some physicians theorizing that it might have been native to the Americas and transported to Europe after 1492. Nevertheless, between the 16th and 19th centuries, syphilis remained among the largest public health crises in existence.
Originally treated with mercury and other poisonous substances, in 1943 it was finally verified that high doses of penicillin successfully combated the early stages of syphilis and resulted in a dramatic decline in the infection worldwide. However, since the turn of the millennium rates of transmission and diagnosis have steadily risen. It is believed that increased promiscuity and prostitution, without the use of protection, in conjunction with the increased spread of other sexually transmitted infections, notably HIV, have spurred this increase. In 2015, an estimated 45.4 million people suffered from syphilis, with at least six million new cases in the same year and 107,000 deaths.