Trichomoniasis
Trichomoniasis
Editor: Jacob McLean
Key Points
- Trichomoniasis is a parasitic infection caused by the protozoan Trichomonas vaginalis.
- It is the most common non-viral sexually transmitted infection in the world.
- People with T. vaginalis infection usually have minimal or no symptoms. However, it commonly causes vaginitis and cervicitis in females patients, and urethritis in both sexes.
- The diagnostic method of choice is the nucleic acid amplification test (NAAT), but other available tests include: wet mount, culture, and rapid antigen test.
- Oral metronidazole or tinidazole are the treatments of choice.
Background & Epidemiology
This is a short (but important!) lesson. Trichomonas vaginalis is an extracellular, flagellated, anaerobic protozoan. T. vaginalis has five flagella - four of which are anterior, and a fifth (posterior) that composes the undulating membrane. It infects the vaginal/cervical epithelium in women, the prostate in men, and the urethra in both sexes.
T. vaginalis is likely the most common non-viral sexually transmitted infection worldwide. It affects both women and men, but the highest prevalence is among women of reproductive age. T. vaginalis is more common among the following groups:
- Females
- Those with multiple sexual partners & who have unprotected sex
- People with a previous history of sexually transmitted infections
- Individuals with low socioeconomic status
Of note, the prevalence of T. vaginalis among men who have sex with men is very low.
Figure 1. Trophozoite of Trichomonas vaginalis
Life Cycle
T. vaginalis lives in the urogenital tract only as a trophozoite (there is no cyst stage!). Humans are its only natural host, and it is transmitted primarily via penile-vaginal intercourse, though fomite transmission has been described among women who have sex with women. The trophozoite exerts a direct cytotoxic effect on the urogenital mucosa, which leads to the typical symptoms of trichomoniasis. T. vaginalis can persist for months in the vagina, though this duration may be shorter in men.
Figure 2. Life cycle of Trichomonas vaginalis
Clinical Presentation
In female patients, trichominiasis principally affects the vaginal canal and cervix. 50-85% of women are asymptomatic, but half of asymptomatic women will become symptomatic within 6 months. The most prominent manifestations among symptomatic women vaginal discharge - which is typically copious and yellow or green in color. Other symptoms include vaginal discomfort, itching, vulvar erythema, dysuria, and dyspareunia. Patients may have punctate cervical hemorrhages (called colpitis macularis or “strawberry cervix”) on colposcopy, but these are rarely seen with the naked eye.
In male patients, the disease fundamentally occurs in the urethra and prostate. Most infectionss are asymptomatic (~80%), but some patients may experience dysuria, urethritis, and rarely prostatitis. T. vaginalis colonization may increase the risk for BPH and prostatic cancer in untreated men.
Rarely, neonates who acquired the disease through the birth canal, may have respiratory complications.
| Clincal syndrome | Symptoms/Signs | |
| Females | Asymptomatic | - |
| Vaginitis/cervicitis | Vaginal discharge, vaginal discomfort, dyspareunia, dysuria | |
| Males | Asymptomatic | - |
| Urethritis/prostatitis | Dysuria, urethral discharge, pelvic pain | |
Table 1. Clinical presentation of trichomoniasis
Diagnosis
- Molecular testing (i.e., NAAT): the modality of choice to diagnose trichomoniasis. Highly sensitive (~90-95%). Can detect low burden of T. vaginalis in the sample, as well as non viable organisms. Vaginal swab is preferred in specimens in female patients, and urine in male patients.
- Others
- Wet mount: visualizes motile microorganisms in the vaginal fluid. T vaginalis remains motile for 10 minutes (needs to be performed quickly!). Sensitivity is 40-80% in experienced hands. Vaginal specimens only.
- Culture: May take up to 2-7 days to incubate. Sensitivity of 80-94%. Able to detect reduced susceptibility to metronidazole/tinidazole. May be commercially available.
- Rapid antigen test: is an immunochromatographic capillary-flow enzyme system that detects T. vaginalis. Highly sensitive and specific. Most not approved for use in male patients
In people living with HIV, all people with receptive vaginal sex, should be screened upon entry to care, and then annually. In people NOT living with HIV, annual screening can be considered in populations at increased risk of infection. Because extragenital infection is rare and of unclear significance, routine screening (oral or rectal) is NOT recommended.
Treatment
| Females | Males | |
| Management | ||
| Preferred regimen | Metronidazole 400-500 q12h x 7 days | Metronidazole 2 gr once |
| Alternative regiment | Tinidazole 2 gr once | Tinidazole 2 gr once | Prevention and control | Safer sex practices (e.g., condom use) Partner notification and treatment Re-test at 3 months |
Safer sex practices (e.g., condom use) Partner notification and treatment Re-test at 3 months |
| Special situations | ||
| Refractory | Oral metronidazole or tinidazole 2 gr daily x 7 days | Oral metronidazole or tinidazole 2 gr daily x 7 days |
| Pregnancy | Refer to preferred regimen | - |
| Metronidazole allergy | Consider desensitization | Consider desensitization |
Table 2. Treatment summary for trichomoniasis
Single-dosed tinidazole may be especially useful for female patients who have difficulties with multi-dose metronidazole due to nausea or other limits to adherence.
Most cases of recurrent trichomoniasis result from reinfection by an untreated sex partner. Current partners should be treated presumptively, and patients should abstain from sex until they an all of their partners complete treatment and have no symptoms.
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References
This is the last lesson for blood and tissue protozoa!
This lesson was last updated August 6 2025