An international study involving the University of Valencia's Cavanilles Institute has demonstrated that the origin of the current strains of the bacteria causing syphilis, Treponema pallidum, subspecies pallidum (TPA), is located in the eighteenth century. The study, published in the journal Nature Microbiology, suggests that the bacteria mutated in the twentieth century, after the discovery and application of penicillin, contributing to the current global expansion of syphilis.