What Causes Trichomoniasis?

Trichomoniasis is a common sexually transmitted disease that is caused by a single-celled, protozoan parasite called Trichomonas vaginalis. The infection can be transmitted from person to person during unprotected vaginal sex. It can also be transmitted during vulva to vulva contact with an infected partner. Pregnant women who have trichomoniasis may have babies who are born early or with low birth weight.

How is trichomoniasis spread?

Sexually active people can get trich by having sex without a condom with a partner who has trich. In women, the infection is most commonly found in the lower genital tract (vulva, vagina, cervix, or urethra). In men, the infection is most commonly found inside the penis (urethra). During sex, the parasite usually spreads from a penis to a vagina, or from a vagina to a penis. It can also spread from one vagina to another vagina. It is not common for the parasite to infect other body parts, like the hands, mouth, or anus. It is unclear why some people with the infection get symptoms while others do not. It probably depends on factors like a person’s age and overall health. People with trich can pass the infection to others, even if they do not have symptoms.


About 70% of people with the infection do not have any signs or symptoms. When trich does cause symptoms, they can range from mild irritation to severe inflammation. Some people get symptoms within 5 to 28 days after getting the infection. Others do not develop symptoms until much later. Symptoms can come and go.

Trichomoniasis in women can cause:

  • abnormal vaginal discharge that may be thick, thin or frothy and yellow-green in colour
  • producing more discharge than normal, which may also have an unpleasant fishy smell
  • soreness, swelling and itching around the vagina – sometimes the inner thighs also become itchy
  • pain or discomfort when passing urine or having sex

Trichomoniasis in men can cause:

  • pain when peeing or during ejaculation
  • needing to pee more frequently than usual
  • thin, white discharge from the penis
  • soreness, swelling and redness around the head of the penis or foreskin


Trichomoniasis can usually be cured with the prescription drug metronidazole or tinizadole given by mouth in a single dose. The symptoms of trichomoniasis in infected men may disappear within a few weeks without treatment. However, an infected man, even a man who has never had symptoms or whose symptoms have stopped, can continue to infect a female partner until he has been treated. Therefore, both partners should be treated at the same time to eliminate the parasite. Persons being treated for trichomoniasis should avoid sex until they and their sex partners complete treatment and have no symptoms. Metronidazole can be used by pregnant women.


Trichomoniasis causes significant morbidity if infections are not treated during pregnancy, including preterm delivery, low birth weight infants, and premature rupture of membranes. Research reveals that trichomoniasis increases the risk of HIV and other STIs. In men, complications may include epididymitis, prostatitis, and infertility.


To prevent infection or reinfection, any sexual partners should also receive treatment.

Ways of preventing the risk of infection or reinfection include:

  • limiting the number of sexual partners
  • avoiding sex for 7–10 days after treatment for trich
  • not using a douche, as this can affect the healthy bacteria in the vagina
  • limiting or avoiding the use of recreational drugs and alcohol, as these increase the risk of unsafe sex
  • using a condom for protection during sex

A condom can prevent transmission to some extent, but it is not fully reliable because the parasite can pass from person to person on areas of the body that it does not cover.

Anyone who has symptoms or thinks that they have been exposed to trich should speak to a doctor.

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