Vaginitis. Artwork of the Trichomonas vaginalis protozoa (blue) that cause vaginitis, with a view inside the vagina of a woman with vaginitis. The neck (cervix) of the uterus is at upper centre. A foul discharge (green) is a symptom of vaginitis, as well as inflammation of the vagina. The body's immune system responds to inflammation and disease through its white blood cells (purple-lobed cells surrounding protozoa). Vaginitis is a sexually transmitted disease (STD) that can be treated with the drug metronidazole if the immune system cannot cope with the infection.