Trichomoniasis
Trichomonas vaginalis is a single celled protozoan parasite that causes trichomoniasis. It is found in the vagina and urethra (mostly in men). Women can aquire trichomoniasis from infected men or women. Men mostly acquire trichomoniasis from infected women. Trichomoniasis is easily curable.
The following sources provide excellent information about this infection:
American Social Health Association