Syphilis is a worm-like spiral-shaped bacterial organism
The explorer Christopher Columbus is responsible for bringing syphilis into Europe, research suggests.
For centuries, controversy has raged over the origin of the infectious disease - whether it was carried from the New World by Columbus and his men.
Now US and Canadian experts who have scrutinised the evolutionary history of the bacterium using molecular genetics say this is most probable.
Critics said the work in PLoS Neglected Tropical Diseases was non-conclusive.
They argue it is still as likely that syphilis emerged in Europe spontaneously, possibly from related bacteria already rife in the Old World, way before Columbus.
The first recorded epidemic of syphilis in Europe broke out among French troops in 1495 - two years after Columbus returned from his first voyage across the Atlantic, prompting speculation that the disease originated in the Americas.
This type of syphilis - Treponema pallidum subspecies pallidum - is spread by sexual intercourse.
Syphilis broke out in France soon after Columbus' first trip to America
The troops, made up largely of mercenaries, returned to their homes and spread the disease across Europe.
But there are other varieties of T. pallidum that are transmitted through skin-to-skin or oral contact.
Kristin Harper from Emory University in Georgia and her team examined the DNA of 23 strains of three common subspecies of T. pallidum, including the sexually transmitted and non-venereal types.
From this they were able to construct a family tree showing how the bacteria had changed over time.
Of all the strains examined, the venereal syphilis-causing strains originated most recently and were most closely related to strains from South America.
"Our results lend support to the Columbian theory of syhpilis' origin while suggesting that the non-sexually transmitted subspecies arose earlier in the Old World," the researchers told PLoS Neglected Tropical Diseases.
But anthropologist Connie Mulligan, from the University of Florida, and colleagues from the University of Texas-Houston Medical School and the University of Washington said the findings were not strong enough to draw any conclusions.
Indeed, some of the findings go against the Columbian theory, they say.
For example, Harper's team found a very high rate of evolutionary change - DNA mutations called single nucleotide polymorphisms (SNPs) - in a bacterium that has classically been characterised by very little genetic change.
"Certainly, firm conclusions should not be based upon a few SNPs in two samples," they said.
A spokesman for the Health Protection Agency said: "This is an interesting study into a disease that, although still relatively rare, has risen substantially over the last decade, with diagnoses now exceeding 3,000 in the UK."