Trichomoniasis: Causes, Symptoms & Treatment

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  • 0:05 Sexually Transmitted Diseases
  • 0:40 Trochomonas Vaginalis
  • 1:08 Life Cycle
  • 1:53 Transmission and Prevention
  • 3:24 Trichomoniasis
  • 5:17 Diagnosis and Treatment
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

Protozoa don't often cause sexually transmitted diseases. One exception is Trichomonas vaginalis. In this lesson we will investigate the major characteristics of this unique parasite.

Sexually Transmitted Diseases

Today we're going to talk about sexually transmitted diseases, but probably not the ones that usually spring to mind. Think about the common STDs you've heard of. Let's narrow the field a bit. We're not talking about the viral STDs like HIV and herpes. You can eliminate the bacterial diseases like syphilis and chlamydia. We're not going to talk about fungal infections or the arthropods like the crab louse. We're going to focus on the one major STD caused by a protozoan: trichomoniasis.

Trichomonas Vaginalis

The protozoan in question is Trichomonas vaginalis, which is a pear-shaped flagellate parasite that only infects the human genitalia. Compared to the horror stories accompanying diseases like herpes and HIV, Trichomoniasis, which is the disease caused by Trichomonas, is relatively benign. In fact, Trichomoniasis has been given the title of most common curable STD.


The lifecycle of Trichomonas is very simple in comparison to some other protozoal parasites. There is only one stage: trophozoite. The trophozoites are motile, infectious, reproductive, and cause the symptoms of the disease. Trichomonas reproduces by simple binary fission and it prefers the slightly acidic environment of the reproductive tracts of infected individuals. Most protozoa have a cyst stage that is infectious and able to survive in the environment. Trichomonas is noteworthy because it is unable to make any cysts. This means it cannot persist for long in the environment and infection occurs by direct contact with viable trophozoites.

Transmission and Prevention

Viable trophozoites can be passed in one of two ways: person-to-person or through contact with contaminated surfaces.

The vast majority of infections are a result of direct sexual contact from person to person. As a result, abstinence is obviously almost 100% effective as a preventative. Proper and consistent condom usage is also effective, but uncovered areas can still transmit the parasite.

Without a cyst stage that can resist environmental conditions, getting Trichomonas from contaminated surfaces is rare, but possible. The trophozoites can survive outside of the host for a couple of hours as long as they stay moist. This makes toilet seats, sauna benches, and wet beach towels potential sources of infection. Fortunately, common household cleaners like bleach are very effective at eliminating the trophozoites from surfaces.

One additional aspect of transmission needs to be addressed. If there is already damage to the genital area, like broken or raw skin, this can make it easier for Trichomonas to attach to host cells and cause disease symptoms. Poor hygiene, diabetes, concurrent infection by other pathogens, and certain drugs can lead to irritation of the genital membranes. This creates a more favorable environment for not only Trichomonas but other disease-causing organisms as well.


Women have a whole set of organisms that appear to live symbiotically in the vagina not causing any kind of disease. These organisms are referred to as the vaginal flora. Trichomonas is so common that it was once considered a member of the normal vaginal flora. Between 25-50% of sexually active women have Trichomonas, compared to only 5% of sexually active men. In the United States, there are 7.4 million new cases of trichomoniasis every year.

Once Trichomonas has colonized the reproductive tract, only about 30% of hosts ever show symptoms. How the disease manifests is dependent on the sex of the host.

The majority of the 30% who show symptoms are women. Trichomonas colonizes the vagina and urethra, causing yellow to green frothy discharge, painful urination, vaginitis, and intense itchiness. These symptoms can be mild or quite severe depending on the health and hygiene of the host. Also, the symptoms generally get worse during menstruation. Pregnant women that become infected can experience premature births and low birth weights due to the parasite weakening or rupturing the placental membranes.

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