Genetic Study Bolsters
Link to Syphilis Columbus
Published: January 15, 2008 the NEW YORK TIMES
(PLoS Neglected Tropical Diseases)
In a comprehensive genetic study, scientists have found what they say is the strongest evidence yet linking the first European explorers of the
The research, they say, supports the hypothesis that returning explorers introduced organisms leading, in probably modified forms, to the first recorded syphilis epidemic, beginning in
Leaders of the new study said the most telling results were that the bacterium causing sexually transmitted syphilis arose relatively recently in humans and was closely related to a strain responsible for the nonvenereal infection known as yaws. The similarity was especially evident, the researchers said, in a variation of the yaws pathogen isolated recently among afflicted children in a remote region of
Researchers who conducted the study and others familiar with it said the findings suggested Columbus and his men could have carried the nonvenereal tropical bacteria home, where the organisms may have mutated into a more deadly form in the different conditions of
Kristin N. Harper, a researcher in molecular genetics at Emory University who was the principal investigator in the study, said the findings supported “the hypothesis that syphilis, or some progenitor, came from the New World.”
The examination of the evolutionary relatedness of organisms associated with syphilis was reported on Monday in the online journal Public Library of Science/Neglected Tropical Diseases.
Ms. Harper, a doctoral student in the Emory department of population biology, ecology and evolution, was the lead author. Her co-authors included George J. Armelagos, an Emory anthropologist who has studied the origins of syphilis for more than 30 years, and Dr. Michael S. Silverman, a Canadian infectious diseases physician who collected and tested specimens from yaws lesions in Guyana, the only known site today of yaws infections in the Western Hemisphere.
The researchers said their study “represents the first attempt to address the problem of the origin of syphilis using molecular genetics, as well as the first source of information regarding the genetic makeup of nonvenereal strains from the
They applied phylogenetics, the study of evolutionary relationships between organisms, in examining 26 geographically disparate strains in the family of Treponema bacteria. Treponema pallidum subspecies pallidum is the agent for the scourge of venereal syphilis. The subspecies endemicum causes bejel, usually in hot, arid climates, and pertenue spreads yaws in hot, humid places.
Della Collins Cook, a paleopathologist at Indiana University who did not participate in the study but specializes in treponemal diseases, praised the research as a “very, very interesting step” advancing understanding of syphilis. “They have looked at a wider range of the genome” of these bacteria, Dr. Cook said, “and have scared up some new samples from parts of the world and the group of related diseases that hadn’t been available to researchers before.”
But she recommended an even broader investigation of the natural history of these diseases, making an effort to find more people with active treponemal cases where they probably still exist in parts of
John W. Verano, an anthropologist at Tulane, said the findings would “probably not settle the debate” over the origins of venereal syphilis, though most scientists had become convinced that the disease was not transmitted sexually before Europeans made contact with the New World.
Donald J. Ortner, an anthropologist at the Smithsonian Institution, questioned whether the organisms causing the first European epidemic were actually distinct from others in the treponemal family. “What we are seeing is an organism with a long history, and it is very adaptable to different modes of transmission that produce different manifestations,” Dr. Ortner said.
Three medical scientists, responding to the new study, pointed out what they considered shortcomings in its methods and interpretations.
In a critique also published by the online journal, Connie J. Mulligan of the University of Florida, Steven J. Norris of the University of Texas at Houston and Sheila A. Lukehart of the University of Washington wrote that caution “must be used in drawing conclusions about the evolution of ‘subspecies’ that may represent a biological continuum, rather than discrete agents.”
“Firm conclusions should not be based,” for example, on the two samples from one location in
But scientists generally agreed that the molecular approach would overcome some
Paleopathologists like Dr. Cook have for years analyzed skeletons for the bone scars from lesions produced by treponemal diseases, except for the mild form called pinta. In this way, they traced the existence of these infections in the
Dr. Cook said the skeletal evidence for treponemal disease in pre-Columbian Europe and Africa was sketchy and even more ambiguous than in the
Scientists remain skeptical of this interpretation. If highly contagious venereal syphilis had existed in
In her investigation, Ms. Harper studied 22 human Treponemal pallidum strains. The DNA in their genes was sequenced in nearly all cases, examined for changes and eventually used in constructing phylogenetic trees incorporating all variations in the strains.
Specimens from two
Ms. Harper’s team concluded that New World yaws belonged to a group distinct from Old World strains, thus occupying the place on the tree more likely to be intermediate between the nonvenereal strains previously existing in
If this seemed to solidify the
Dr. Armelagos said research into the origins of syphilis would continue, because “understanding its evolution is important not just for biology, but for understanding social and political history.”
Noting that the disease was a major killer in Renaissance Europe, he said, “It could be argued that syphilis is one of the important early examples of globalization and disease, and globalization remains an important factor in emerging diseases.”