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Infectious Voyagers: DNA suggests Columbus took syphilis to Europe

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4:33pm, January 16, 2008
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Goodbye Columbus, hello syphilis. When Renaissance-era folk bade farewell to Christopher Columbus and his crew, little did they know that the New World explorers would return with syphilis infections that eventually triggered devastating outbreaks of the sexually transmitted disease in Europe.

That's the implication of the first study to probe the genetic makeup and evolutionary relationships of strains of bacteria, known as treponemes, that cause syphilis and related diseases.

"Our data support the hypothesis that syphilis, or some progenitor of it, came from the New World," says geneticist Kristen N. Harper of Emory University in Atlanta, who directed the new investigation.

The first recorded syphilis epidemic in Europe occurred in 1495. Scientists have argued for decades about whether syphilis originated in the Americas and spread elsewhere via European explorers or arose much earlier in Europe.

Prior research analyzed skeletal damage presumably caused by chronic syphilis. The age of such material and its attribution to syphilis rather than to other diseases remain controversial.

Harper's team isolated 21 genetic regions from 26 strains of treponemes found in various parts of the world. The researchers obtained samples of these strains from collections in North America and Europe.

These bacteria cause distinct diseases that share some symptoms but spread in different ways. Syphilis proliferates through sexual contact. Yaws and endemic syphilis, characterized by similar reddish sores around the mouth and other areas, primarily affect children through skin-to-skin or oral contact. Although both diseases have been largely eradicated, yaws historically infected people in hot, humid locales, whereas endemic syphilis occurred in hot, dry regions.

A fourth strain, pinta, was once found in Central and South America and mainly caused skin discolorations.

By examining the frequency of alterations to the gene sequences of different strains, the investigators distinguished between older and younger strains and identified evolutionary relationships among them. The analysis could not estimate the absolute ages of various strains.

In a critical comparison, Harper's team also examined a never-before studied strain of yaws obtained by medical workers from two members of a relatively isolated foraging group in Guyana.

Syphilis-causing bacterial strains arose recently and resemble the yaws strain from Guyana, the researchers report in the January PLoS Neglected Tropical Diseases.

Yaws originated in the Old World, before evolving and spreading with humans to the Middle East and Eastern Europe as endemic syphilis, and then to the Americas as yaws, the team proposes. European explorers then brought a yaws strain back to the Old World. It evolved into a precursor of modern syphilis strains.

However, that scenario is uncertain, contend immunologist Sheila A. Lukehart of the University of Washington, Seattle, and her coworkers in a comment published with the new report. The accuracy of genetic signatures for different treponeme strains has yet to be established, they say.

Moreover, the new analysis compares only a handful of genetic alterations that may have emerged relatively quickly, making it difficult to reconstruct evolutionary relationships, Lukehart holds.

Harper and Lukehart agree that to settle such issues, scientists next need to sequence whole genomes of different treponeme strains.

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