Trichomonas vaginalis, a flagellate protozoan, is the most common pathogenic protozoan of humans in industrialized countries. It is found worldwide and exhibits a higher prevalence among persons with multiple sexual partners or other venereal diseases.
Trichomonas vaginalis resides in the female lower genital tract and the male urethra and prostate, where it replicates by binary fission. The parasite does not appear to have a cyst form, and does not survive well in the external environment. Trichomonas vaginalis is transmitted among humans, its only known host, primarily by sexual intercourse.