Why do some historians think syphilis may have reached Europe from the New World?

The theory that syphilis originated in the New World is primarily supported by the timing of its appearance in European records and biological evidence found in the Americas.

Historians and scientists point to the fact that there are no indisputable references to the disease in European literature prior to the return of Christopher Columbus from the New World. Following his return, a rapidly spreading epidemic emerged across Europe, which was initially referred to by various names such as the "Great Pox".1

Further support for the New World origin theory comes from the discovery of treponematosis in the skeletal remains of pre-Columbian American Indians. While some researchers suggest that cases previously diagnosed as leprosy in Europe before 1500 may have actually been syphilis—due to shared characteristics like perceived contagiousness and response to mercury therapy—the sudden, widespread outbreak following the late 15th-century transatlantic voyages remains a central pillar of the New World hypothesis.1