Trichomonas vaginalis is a protozoan (a single-celled organism that is bigger and more complex than a bacterium) that infects the genital tracts of both women and men. Trichomonas is almost always a sexually transmitted infection.

The majority (50-80 percent) of women and some men infected with trichomonas do not know that they are infected.4 In women, trichomonas causes vaginitis (inflammation of the vagina) and cervicitis (inflammation of the cervix). Symptoms of trichomonas vaginitis/ cervicitis frequently include vaginal discharge, abnormal vaginal bleeding (typically after intercourse) due to cervical irritation, swelling and irritation of the genitals, itching of the vulva and abdominal pain. In men, the urethra (tube carrying fluid from the bladder out the penis) is the most common location of infection. Symptoms of urethritis (infection of the urethra) include discharge from the penis and burning with urination.

Patients with symptoms are usually diagnosed when the clinician finds characteristic physical findings and identifies the trichomonas organism in genital fluids (vaginal or urethral discharge) or urine. Routine testing for trichomonas infection is not normally done in patients without symptoms, so infected individuals who don’t have symptoms are unlikely to be tested. Unfortunately, these asymptomatic individuals may transmit the infection to their sexual partners without being aware of the risk. Most trichomonas infections are treated with metronidazole, a drug that is taken by mouth. The most common side effect of metronidazole is a gastrointestinal reaction some patients have after taking metronidazole and then consuming alcoholic beverages. Trichomonas infection in pregnant women is associated with premature rupture of membranes (early breakage of the fluid sac surrounding a developing baby) and preterm labor.Finally, when a person has a trichomonas infection and then has sex with an HIV-infected person, his/her risks of contracting HIV may be increased.6 (HIV is the virus that causes AIDS.)

Since trichomonas is transmitted by exchange of body fluids, condoms are likely to reduce the risk of transmission in sexually active individuals. As with other STIs, however, condoms provide incomplete protection.  And because most infected individuals are unaware of their infection, having a sexual partner who is not having symptoms of infection offers no protection against infection. If you have already been sexually active outside a lifelong mutually faithful relationship (as in marriage), talk to your healthcare provider about getting you and your partner tested for STDs. Abstinence from sexual activity or lifetime faithfulness to one uninfected partner is the only certain way to avoid being infected sexually. Read more at

1. Krieger JN, Alderete JF. Trichomonas vaginalis and trichomoniasis. In: Holmes KK, Mardh PA, Sparling PF, et al., eds. Sexually Transmitted Diseases. 3rd ed. New York, NY: McGraw Hill, Co.; 1999:587-604. 2. American Social Health Association. Sexually Transmitted Diseases in America: How Many Cases and at What Cost? Menlo Park, CA: Kaiser Family Foundation; 1998. 3. Krieger JN, Alderete JF. Trichomonas vaginalis and trichomoniasis. In: Holmes KK, Mardh PA, Sparling PF, et al., eds. Sexually Transmitted Diseases. 3rd ed. New York, NY: McGraw Hill, Co.; 1999:587-604. 4. Ibid. 5. Ibid. 6. Laga M, Manoka A, Kivuvu M, et al. Non-ulcerative sexually transmitted diseases as risk factors for HIV-1 transmission in women: Results from a cohort study.  AIDS. 1993;7:95-102.

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