National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention
Division of Sexually Transmitted Diseases
Program and Training Branch
Pathogenesis and Microbiology
The etiologic agent in trichomoniasis is Trichomonas vaginalis, which is a flagellated anaerobic protozoa. It is the only protozoan that infects the genital tract. T. vaginalis has four free flagellae and one flagella embedded in an undulating membrane. The flagellae are responsible for the jerky motility of this organism that is seen under a microscope.
Trichomonas infections are not routinely tested in men. However, a recent study reported the prevalence of T. vaginalis was 17% in men attending an urban STD clinic.