According to the US Centers for Disease Control and Prevention (CDC), trichomoniasis is a common sexually transmitted infection (STI). However, not many have heard of this infection. Trichomoniasis is a condition that is caused by a parasite called Trichomonas vaginalis. This STI can lead to symptoms such as a swollen vulva, white, gray, yellow, or green vaginal discharge and/or a fishy vaginal odor.