June 14, 2008 Variations in a gene within the family of bacteria that causes syphilis may hold clinical, epidemiological and evolutionary significance, researchers at Emory University in Atlanta have found.
The researchers' study results describe how sequence variations they identified in the acidic repeat protein (ARP) gene allow straightforward differentiation of venereal syphilis from non-venereal Treponema pallidum subspecies.
"This finding can lead to improved diagnoses of cases, enabling doctors to prescribe the right treatment, and public health workers to determine the best prevention strategies," says Kristin Harper, who led the research team as a Howard Hughes Medical Institute pre-doctoral fellow in EmoryÕs Population Biology, Ecology and Evolution program.
The family of Treponema bacteria causes venereal syphilis and the non-venereal diseases of yaws and bejel, which are transmitted through skin-to-skin or oral contact. Public health workers in parts of Africa have reported difficulty in distinguishing yaws from syphilis in children, leaving open the question of whether the child may have contracted a venereal disease Ð either congenitally or through sexual abuse.
"As yaws eradication efforts near their goal, and case diagnosis becomes more difficult due to the relative rarity of yaws, a molecular means of determining whether the infection is venereal or non-venereal becomes essential," Harper says.
The analysis of the repeat region of the ARP gene in 32 strains of pathogenic Treponema showed that the sexually transmitted strains contained multiple types of repeat motifs, while the non-venereal subspecies contained only one type of motif.
In addition, the researchers found the presence of multiple, but distinct, repeat motifs in the two types of sexually transmitted Treponema examined, suggesting that a diverse repertoire of repeat motifs has evolved at least two times in association with sexual transmission.
"The kind of changes we found in the ARP gene are consistent with rapid evolution," Harper said. "This scenario lends further support to several prominent theories about the origin of syphilis, including that the pathogen arose with the return of Columbus from the New World."
Harper was assisted in her research by Paolo Ocampo of Emory's School of Medicine; George Armelagos, chair of Emory's Department of Anthropology; and scientists at the Centers for Disease Control and Prevention. Previously, Harper headed up the most comprehensive comparative genetic analysis ever conducted on Treponema bacteria. The results were published in January by the Public Library of Science's Journal of Neglected Tropical Diseases.
Harper is currently researching an outbreak of treponemal disease among baboons in Tanzania, which could provide another important genetic clue to how the disease is transmitted in humans.
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- Harper et al. The sequence of the acidic repeat protein (arp) gene differentiates venereal from nonvenereal Treponema pallidum subspecies, and the gene has evolved under strong positive selection in the subspecies that causes syphilis. FEMS Immunology & Medical Microbiology, 2008; 0 (0): 080612073358959 DOI: 10.1111/j.1574-695X.2008.00427.x
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