| Trichomonas vaginalis, the causative agent of human trichomoniasis, is the most prevalent non-viral sexually transmitted infection world-wide. Although associated with increased risk of HIV transmission, making its detection and treatment a global health priority, little is known about its diversity or population structure. We developed a panel of T. vaginalis genetic markers, including 21 microsatellites and six single-copy genes, to evaluate the population genetics of: 18 clinical isolates collected from female patients attending New York City STD clinics in 2008; 177 isolates from ten global regions; 174 samples from 123 HIV-infected female patients in the U.S.A; and 32 strains associated with vaginal microbiome data. We find the species to be genetically diverse with a striking, globally-distributed population structure consisting of two 'types' (type 1 and type 2). We find that parasite types are associated with certain clinical traits; for example, when compared to type 2 parasites, type 1 parasites have a higher in vitro growth rate, more frequently harbor a dsRNA virus, are more sensitive to metronidazole in vitro, cause more disruption to the vaginal microbiota, and are associated with higher viral loads in HIV-positive women. In addition, we uncover evidence of genetic exchange, suggesting a sexual life-cycle of the parasite despite an absence of morphologically-distinct sexual stages and indicating that recombination has played an important role in evolution of the T. vaginalis genome. Together our findings are important for understanding the spread and mechanisms of drug resistance, for characterizing virulence factors, and in understanding why many individuals remain asymptomatic while others have severe manifestations of disease. |
