Causal Agent:
Trichomonas vaginalis, a flagellate, is the most common pathogenic protozoan of humans in industrialized countries.

Life Cycle:

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 .

Geographic Distribution:
Worldwide.  Higher prevalence among persons with multiple sexual partners or other venereal diseases.