Trichomoniasis-Cause Trichomoniasis (trich) is caused by a tiny parasite (a one-celled protozoan) that most commonly is sexually transmitted from an infected person.

In women, trich organisms usually infect the vagina and cervix, urethra, bladder, and glands in the genital area, such as the Bartholin's and Skene's glands.

In men, infections develop in the urethra or under the foreskin of an uncircumcised penis.