CHICAGO - New genetic evidence supports the theory that Christopher Columbus brought syphilis to Europe from the New World, US researchers said Monday, reviving a centuries-old debate about the origins of the disease.

They said a genetic analysis of the syphilis family tree reveals that its closest relative was a South American cousin that causes yaws, an infection caused by a sub-species of the same bacteria.

"Some people think it is a really ancient disease that our earliest human ancestors would have had. Other people think it came from the New World," said Kristin Harper, an evolutionary biologist at Emory University in Atlanta.

"What we found is that syphilis or a progenitor came from the New World to the Old World and this happened pretty recently in human history," said Harper, whose study appears in journal Public Library of Science Neglected Tropical Diseases.

She said the study lends credence to the "Columbian theory," which links the first recorded European syphilis epidemic in 1495 to the return of Columbus and his crew.

"When you put together our genetic data with that epidemic in Naples in 1495, that is pretty strong support for the Columbian hypothesis," she said.

Syphilis, a sexually transmitted disease caused by the bacterium Treponema pallidum, starts out as a sore, but progresses to a rash, fever, and eventually can cause blindness, paralysis and dementia.

Most recent evidence of its origins comes from skeletal remains found in both the New World and the Old World. Chronic syphilis can leave telltale lesions on bone. "It has a worm-eaten appearance," Harper said in a telephone interview.

SYPHILIS FAMILY TREE

Harper used an approach that examines the evolutionary relationships between organisms known as phylogenetics. She looked at 26 strains of Treponema, the family of bacteria that give rise to syphilis and related diseases like bejel and yaws, typically a childhood disease that is transmitted by skin-to-skin contact.

The study included two strains of yaws from remote areas of Guyana in South America that had never been sequenced before.

"We sequenced 21 different regions trying to find DNA changes between the strains," Harper said.

They concluded that while yaws is an ancient infection, venereal syphilis came about fairly recently. Harper suspects a nonvenereal subspecies of the tropical disease quickly evolved into venereal syphilis that could survive in the cooler, European climate.

But it is not clear how this took place. "All we can say is the ancestor of syphilis came from the New World, but what exactly it was like, we don't know," she said.

In a commentary published in the same journal, Connie Mulligan of the University of Florida and colleagues disagreed with Harper's analysis, suggesting her conclusions relied too heavily on genetic changes from the Guyana samples.

Mulligan suggested that better clues would come from DNA extracted from ancient bones or preserved tissues.

Harper concedes that more work needs to be done to explain the journey of syphilis to the New World. "This is a grainy photograph," she said.