Published online 14 January 2008 | Nature | doi:10.1038/news.2008.425

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Syphilis: spoil of the New World?

Genetic study blames Columbus for bringing syphilis to Europe.

Researchers have long debated the origins of the syphilis-causing bacterium.CDC

For more than 500 years, Christopher Columbus has been alternately blamed and exonerated for bringing syphilis to Europe. Now, a genetic analysis of the disease-causing bacteria shows that today's syphilis is a close cousin to the South American tropical disease yaws, suggesting that the malady has its roots in the Americas.

"What we have shown here using genetics is that syphilis travelled from the New World to the Old World relatively recently in human history," says microbiologist Kristin Harper of Emory University in Atlanta, Georgia, who reports the work this week in the journal PLoS Neglected Tropical Diseases1. As the first recorded syphilis outbreak occurred in 1495 during Charles the VIII’s invasion of Naples, Harper says that syphilis probably arrived in Europe with Columbus, who had just come back from the New World two years before.

Since the 16th century, debate has raged on the geographic origins of syphilis (Treponema pallidum), a spiral-shaped bacterium that causes cardiovascular and neurological damage.

For decades, palaeopathologists have attempted to pinpoint the origins of syphilis by looking for tell-tale scars on the bones of ancient skeletons, an effect of later stages of the disease. In 2000, a skeleton found in a friary in northeastern Britain seemed to show evidence of bone lesions caused by syphilis2, and initial dating suggested that the man had died at least 50 years before Columbus’ first voyage, letting the explorer off the hook. But anthropologists later said that the dating may have been complicated by the fishy diet of the region, making the skeleton seem older than it is. No definitive conclusions have since been reached.

Genetic insight

Genetics promised an alternative way to settle the Columbus debate. By comparing genetic sequences from various subspecies of Treponema around today, researchers should be able to unpick their history.

Harper and her colleagues analysed 22 human Treponema samples, including two collected from a Guyanese village with an active outbreak of yaws (T. pertenue). Unlike syphilis — a sexually transmitted disease — yaws is usually spread through skin contact. But it is thought to be a close cousin of syphilis, and the South American variety is a good candidate for the source of the venereal disease.

Unfortunately, the two Guyanese samples were heavily damaged by tropical heat. But the researchers could salvage some sections of the genome, including 17 base pairs that vary widely between different Treponema samples and so are diagnostic of different subspecies. Between syphilis and South American yaws, 4 of these 17 base pairs were identical. The overlap with any other kind of Treponema was limited to one or none of the sites.

A phylogenetic tree of the Treponema samples also showed that syphilis had evolved most recently of the bacterial strains studied.

Not dead yet

"I think it’s a very significant paper," says anthropologist Shelley Saunders of McMaster University in Ontario. "It was obvious that what was needed was some group that could go and collect as many strains of Treponema as they could." Few strains of syphilis are stored for study, and the bacteria are notoriously fragile.

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"Unfortunately, the two key strains are these two T. pertenue strains from Guyana," says human geneticist Connie Mulligan of the University of Florida. Mulligan, who authored a commentary that accompanies Harper’s paper, says that the limited genetic information from the crucial Guyana samples and the possible complexity of the genetic evolution of the bacteria cloud the picture of where syphilis came from. So the work isn't yet firm proof that T. pallidum evolved from T. pertenue, she says.

Harper says that more work remains to be done and plans to sequence full genomes to investigate the history of the bacterium. "What we have now is a grainy photograph. But if we had the full genome [of all the different Treponema], we could get a much clearer picture of what happened," says Harper. 

  • References

    1. Harper, K. N. et al. PLoS Negl. Trop. Dis. 2, e148 (2008). | Article |
    2. Morton, R. S. & Rashid, S. Sex. Transm. Inf. 77, 322-324 (2001). | Article | ChemPort |
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