Trichomonas vaginalis."> Trichomoniasis - Intelihealth


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Harvard Medical School
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Sexually Transmitted Diseases
Common Sexually Transmitted Diseases
Trichomoniasis, nicknamed "trick", is a sexually transmitted disease (STD) caused by a microscopic one-celled organism called Trichomonas vaginalis.
InteliHealth/Harvard Medical Content

What Is It?

Trichomoniasis, nicknamed "trick," is a sexually transmitted disease (STD) caused by a microscopic one-celled organism called Trichomonas vaginalis. Trichomoniasis can cause vaginal infections in women and inflammation of the urethra (the tube that drains urine from the bladder) in both sexes. In pregnant women, Trichomonas infections also can increase the risk of premature rupture of the membranes and preterm delivery.

Trichomonas is passed from an infected person to his or her partner during sexual intercourse without a condom. Currently, Trichomonas infections affect approximately 3 million women in the United States each year. Men can pass the infection on to their sexual partners, but they rarely develop symptoms themselves.


In women, Trichomonas organisms can live in the vagina for many years without causing symptoms. If symptoms occur, they can include:

  • A yellow-green, foul-smelling vaginal discharge
  • Vaginal pain or itching
  • Irritation and inflammation around the vaginal opening
  • Vaginal pain during sexual intercourse
  • Burning discomfort during urination

In rare cases there will be discomfort in the lower abdomen. Symptoms may be worse during a menstrual period. Although men usually have no symptoms, they occasionally can have irritation and inflammation at the tip of the penis, discomfort during urination, and a discharge from the end of the penis.


Once you describe your symptoms, your doctor will check your vagina or urethra for inflammation and abnormal discharge, and do a pelvic examination. During the exam, he or she will collect a specimen with a swab, and send it to a laboratory to be examined. Trichomoniasis can be diagnosed by viewing the parasite under the microscope in the office or more accurately by culturing it in the laboratory. Because people with Trichomonas infections are more likely to get other STDs, your doctor also may perform tests for gonorrhea, chlamydia, syphilis and HIV.

Expected Duration

Without treatment, Trichomonas infections can last for years.


Because trichomoniasis can be transmitted during sexual activity, you can help to prevent infection by:

  • Not having sex
  • Having sex with only one uninfected sex partner
  • Consistently using male latex condoms during sexual intercourse


Trichomonas infections are best treated with an oral medication called metronidazole (Flagyl, Metryl). Although metronidazole gel is also available, it is not as effective as medication taken by mouth. To prevent becoming infected again, all sex partners of an infected person must be treated and refrain from intercourse until treatment is complete. Pregnant women should not take metronidazole during the first trimester of pregnancy, so an alternative medication should be used or treatment should be delayed until later in pregnancy. In people who drink alcohol, metronidazole can trigger cramps, nausea, vomiting, headaches and flushing. To prevent these problems, avoid drinking alcoholic beverages while taking metronidazole and for three days after you stop taking the drug.

When to Call a Professional

If you are a woman, call your doctor whenever you have vaginal discomfort or an abnormal vaginal discharge, especially if you are pregnant. If you are a man, call your doctor whenever you have redness or discomfort around the end of your penis.


Oral metronidazole cures trichomoniasis in 90% to 95% of cases. If the condition is not cured, it is often because the infected person's sex partner has not been treated and continues to transmit Trichomonas.

Additional Info

American Social Health Association
P.O. Box 13827
Research Triangle Park, NC 27709
Phone: 919-361-8400
Fax: 919-361-8425

CDC National Prevention Information Network (NPIN)
National Center for HIV, STD and TB Prevention
P.O. Box 6003
Rockville, MD 20849-6003
Toll-Free: 1-800-458-5231
Fax: 1-888-282-7681

10680, 10900, 29362,
metronidazole,sex,inflammation,medication,penis,hiv,std,urethra,vagina,vaginal discharge
Last updated October 31, 2011

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