The sexually transmitted disease caused by a single-celled protozoan parasite and usually cured with metronidazole is trichomoniasis. It is caused by Trichomonas vaginalis and is the most common non-viral STI worldwide, infecting an estimated 180 million people annually.
Symptoms may include genital itching, irritation, burning, pain, foul-smelling discharge, and a strawberry cervix, though many infected people are asymptomatic. Treatment typically consists of a single dose of metronidazole or tinidazole.