%0 Journal Article %A Šmajs, David %A Mikalova, Lenka %A Strouhal, Michal %A Grillova, Linda %D 2016 %I Begell House %K microbial evolution, syphilis, Treponema pallidum subsp. pallidum %N 3-4 %P 181-190 %R 10.1615/ForumImmunDisTher.2017020184 %T Why Are There Two Genetically Distinct Syphilis-Causing Strains? %U https://www.dl.begellhouse.com/journals/2c6306423483e001,6deddb8911c6adff,3170ddbd1bdada57.html %V 7 %X Genetic analyses of Treponema pallidum subsp. pallidum (TPA) reference strains and human clinical isolates have revealed that there are two genetically distinct groups of TPA strains, one group related to the reference strain TPA Nichols (Nichols-like strains) and the second to the TPA SS14 strain (SS14-like strains). In general, the diversification of syphilis-causing strains into SS14- and Nichols-like groups is consistent with geographical and population separation of syphilis-infected human societies, such as separation of American and European populations before the 15th century, and this isolation could explain the missing intermediates between the two groups of TPA strains. In addition, whereas SS14-like strains are predominant among contemporary worldwide clinical isolates, a predominance of Nichols-like strains among reference laboratory strains (isolated in the United States during the 1900s) was found. The possible reasons for these discrepancies are discussed, but the ultimate reasons of both the diversification of syphilis-causing strains into SS14- and Nichols-like groups as well as the contemporary worldwide predominance of SS14-like strains in the human population remain unknown. %8 2017-10-11