Causes and Risk Factors of Trichomoniasis

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Trichomoniasis is a sexually transmitted disease caused by a sexually transmitted organism known as Trichomonas vaginalis or T. vaginalis. It is the most common curable sexually transmitted infection in the United States and around the world.

However, when left untreated, it is associated with an increased risk of a number of long-term health problems. These include HIV, pelvic inflammatory disease, and various complications of pregnancy. Unfortunately, many cases of trichomoniasis are left untreated because the disease is often asymptomatic. Therefore, it frequently goes undetected in populations where there isn't routine screening. 

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Common Causes

Trichomoniasis is caused by Trichomonas vaginalis. 

Unlike many organisms that cause sexually transmitted diseases (STDs),  T. vaginalis is neither a bacteria or a virus. It is a protozoa. More specifically, it is a protozoan flagellate.

That means that trichomonas is a one-celled organism with a tail (flagellum) that it uses to swim around. Under a microscope, these parasites are easy to recognize on a vaginal swab. The big round head and long tail of T. vaginalis looks like nothing else that is commonly found in a vaginal sample. 

The trichomonas parasite is transmitted by exposure to infected secretions, generally vaginal fluid or semen. The parasite can infect the cervix, vagina, and the urethra in women and the urethra in men.

Trichomoniasis symptoms may never appear, or they may appear months or years after infection. Women are more likely to have symptoms than men, and they are also more likely to be treated. This can be problematic as having an untreated partner means there is a high risk of re-infection. This is also why people are encouraged to be sexually abstinent during treatment.

Lifestyle Risk Factors

Reliably and consistently practicing safe sex significantly reduces your risk of getting trichomoniasis. If you use condoms or other barriers every time you have sex, it is relatively unlikely that you will be exposed to this disease. Similarly, if both you and your partner have been screened for STDs, test negative for trichomoniasis, and are in a mutually monogamous relationship, your risk is negligible. 

There are several groups who have higher than average rates of trichomoniasis. These groups include:

  • non-Hispanic black women
  • incarcerated individuals
  • STD clinic patients
  • recent drug users
  • people infected with HIV

It is thought that most cases of trichomoniasis are spread through heterosexual vaginal intercourse.

Trichomoniasis can be spread through vulva-to-vulva contact. Though uncommon, it may also be transmitted through oral and anal sex. It is unclear, however, if people have sustained infections at those sites. Unfortunately, our understanding of the role of anal and oral sex in trichomoniasis transmission is complicated by the fact that doctors rarely test for trichomoniasis at those sites.

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Article Sources

  1. STD Facts - Trichomoniasis. Centers for Disease Control and Prevention. Updated January 31, 2017.


  2. Patel EU, Gaydos CA, Packman ZR, Quinn TC, Tobian AAR. Prevalence and Correlates of Trichomonas vaginalis Infection Among Men and Women in the United States. Clin Infect Dis. 2018;67(2):211-217. doi:10.1093/cid/ciy079


  3. Trichomoniasis: MedlinePlus Medical Encyclopedia. MedlinePlus. Updated December 1, 2018.


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