Extensive Genetic Diversity, Unique Population Structure and Evidence of Genetic Exchange in the Sexually Transmitted Parasite Trichomonas vaginalis

Abstract

Background Trichomonas vaginalis is the causative agent of human trichomoniasis, the most common non-viral sexually transmitted infection world-wide. Despite its prevalence, little is known about the genetic diversity and population structure of this haploid parasite due to the lack of appropriate tools. The development of a panel of microsatellite makers and SNPs from mining the parasite's genome sequence has paved the way to a global analysis of the genetic structure of the pathogen and association with clinical phenotypes. Methodology/Principal Findings Here we utilize a panel of T. vaginalis -specific genetic markers to genotype 235 isolates from Mexico, Chile, India, Australia, Papua New Guinea, Italy, Africa and the United States, including 19 clinical isolates recently collected from 270 women attending New York City sexually transmitted disease clinics. Using population genetic analysis, we show that T. vaginalis is a genetically diverse parasite with a unique population structure consisting of two types present in equal proportions world-wide. Parasites belonging to the two types (type 1 and type 2) differ significantly in the rate at which they harbor the T. vaginalis virus, a dsRNA virus implicated in parasite pathogenesis, and in their sensitivity to the widely-used drug, metronidazole. We also uncover evidence of genetic exchange, indicating a sexual life-cycle of the parasite despite an absence of morphologically-distinct sexual stages. Conclusions/Significance Our study represents the first robust and comprehensive evaluation of global T. vaginalis genetic diversity and population structure. Our identification of a unique two-type structure, and the clinically relevant phenotypes associated with them, provides a new dimension for understanding T. vaginalis pathogenesis. In addition, our demonstration of the possibility of genetic exchange in the parasite has important implications for genetic research and control of the disease.

Genetic Characterization of Trichomonas vaginalis Isolates by Use of Multilocus Sequence Typing

“…Microsatellite markers have been used to characterize the genetic diversity and population structure of several protozoan pathogens, including Leishmania tropica, Trypanosoma cruzi, Trypanosoma brucei gambiense, Plasmodium species, and Toxoplasma gondii (2,6,8,12,29,30,44,53,55). Recently, the usefulness of microsatellite makers to assess the genetic diversity and transmission of T. vaginalis has also been demonstrated (10,11,46). However, the generally high mutation rate of microsatellite markers can cause homoplasy, which may distort the inferred evolutionary history of a species (19).…”

Unique <i>Trichomonas vaginalis</i> gene sequences identified in multinational regions of Northwest China

“…These studies had been done on the genotype of T. vaginalis and the relationship between its genotype and the clinical presentation of trichomoniasis, including metronidazole susceptibility, the presence of T. vaginalis virus (TVV) and Mycoplasma hominis (6)(7)(8)(9). In this study, all the samples were collected from Xinjiang and the low Our results demonstrated that the genetic diversity of Chinese T. vaginalis isolates was associated with geographic distance based on the 18S ribosomal RNA gene.…”

“…Several T. vaginalis sequences have been reported to date, and most of the 18S gene sequences have been reported in Chinese and Philippine studies (17)(18)(19). Previous studies indicate a relationship between T. vaginalis genotype and the clinical presentation of trichomoniasis (7,20,21). In this study, a distancebased network was constructed with three large clusters and many branches.…”

“…For example, the 18S ribosomal RNA gene is conserved in primary structure, making it a good target for detecting T. vaginalis by PCR. In addition, PCR-based gene sequencing has been used to examine T. vaginalis genotypes (6)(7)(8)(9). Conrad et al used 27 polymorphic markers, including 21 microsatellite and 6 single-copy genes, to study genetic diversity in T. vaginalis and identified two population types (6).…”

“…Conrad et al used 27 polymorphic markers, including 21 microsatellite and 6 single-copy genes, to study genetic diversity in T. vaginalis and identified two population types (6). Previous studies had also been done on the relationship between its genotype and the clinical presentation of trichomoniasis, including drug susceptibility and microbial symbiosis (6)(7)(8)(9).…”