The first well-recorded European outbreak of what is now known as syphilis occurred in 1495 among French troops besieging Naples, Italy. It may have been transmitted to the French via Spanish mercenaries serving King Charles of France in that siege. From this centre, the disease swept across Europe. As Jared Diamond describes it, "When syphilis was first definitely recorded in Europe in 1495, its pustules often covered the body from the head to the knees, caused flesh to fall from people's faces, and led to death within a few months." The disease then was much more lethal than it is today. Diamond concludes,"By 1546, the disease had evolved into the disease with the symptoms so well known to us today." The epidemiology of this first syphilis epidemic shows that the disease was either new or a mutated form of an earlier disease.
Researchers concluded that syphilis was carried from the New World to Europe after Columbus' voyages. Many of the crew members who served on this voyage later joined the army of King Charles VIII in his invasion of Italy in 1495, resulting in the spreading of the disease across Europe and as many as five million deaths. The findings suggested Europeans could have carried the nonvenereal tropical bacteria home, where the organisms may have mutated into a more deadly form in the different conditions and low immunity of the population of Europe. Syphilis was a major killer in Europe during the Renaissance. In his Serpentine Malady (Seville, 1539) Ruy Diaz de Isla estimated that over a million people were infected in Europe.