What is Trichomonas vaginalis and how is it treated?

Trichomonas Vaginalis and Its Treatment

Trichomonas vaginalis is a protozoan parasite that causes the most common curable sexually transmitted infection worldwide, and the recommended first-line treatment is metronidazole 2 g orally in a single dose. 1

What is Trichomonas Vaginalis?

Trichomonas vaginalis is a flagellated protozoan parasite that causes trichomoniasis, a sexually transmitted infection with the following characteristics:

• In women:

  • Many infected women experience symptoms including a diffuse, malodorous, yellow-green vaginal discharge with vulvar irritation 1
  • However, some women have minimal or no symptoms 1
  • Can lead to adverse pregnancy outcomes including premature rupture of membranes, preterm delivery, and low birth weight 1
  • Associated with increased risk of HIV acquisition and transmission 2
  • Linked to increased risk of cervical cancer 2

• In men:

  • Most infected men are asymptomatic 1
  • Some may develop non-gonococcal urethritis (NGU) 1
  • Potential association with prostate cancer 2

Diagnosis

Diagnosis of trichomoniasis can be made through several methods:

1. Microscopy: Examination of vaginal secretions, but has limited sensitivity (60-70%) 1

2. Culture: Most sensitive commercially available method of diagnosis 1

3. Nucleic Acid Amplification Tests (NAATs): Becoming the new gold standard for diagnosis, replacing culture due to higher sensitivity 3

Treatment Recommendations

First-line Treatment:

• Recommended regimen: Metronidazole 2 g orally in a single dose 1

Alternative Treatment:

• Alternative regimen: Metronidazole 500 mg twice a day for 7 days 1

Treatment Efficacy:

• Both recommended metronidazole regimens result in cure rates of approximately 90-95% 1
• Treatment of both patient and sex partners increases cure rates and reduces transmission 1

Management of Sex Partners:

• Sex partners should be treated 1
• Patients should avoid sex until both they and their partners have completed treatment and are asymptomatic 1

Treatment Failures and Resistance

If treatment failure occurs:

1. First failure: Re-treat with metronidazole 500 mg twice daily for 7 days 1
2. Second failure: Treat with a single 2 g dose of metronidazole once daily for 3-5 days 1
3. Persistent failure: Consult with a specialist; consider determining T. vaginalis susceptibility to metronidazole 1

Drug resistance is an emerging concern:

• Resistance to metronidazole is increasingly reported 4
• Cross-resistance among 5-nitroimidazole drugs is common 4
• Tinidazole is an alternative 5-nitroimidazole drug approved for trichomoniasis treatment 5

Special Populations

Pregnancy:

• Symptomatic pregnant women should be treated to ameliorate symptoms 1
• Can be treated with metronidazole 2 g in a single dose, even during pregnancy (after first trimester) 1
• Multiple studies have not demonstrated consistent teratogenic or mutagenic effects of metronidazole in infants 1

HIV Infection:

• Patients with HIV should receive the same treatment regimen as those without HIV 1

Metronidazole Allergy:

• Patients with immediate-type allergy to metronidazole can be managed by desensitization 1
• Topical therapy with non-nitroimidazole drugs can be attempted but has low cure rates (<50%) 1

Common Pitfalls and Caveats

1. Underdiagnosis: Due to asymptomatic nature in many cases, especially in men, infections often go undetected 6

2. Inadequate testing: Relying solely on wet mount microscopy misses many infections due to its low sensitivity 2

3. Failure to treat partners: Not treating sexual partners leads to reinfection and persistent symptoms 1

4. Topical metronidazole ineffectiveness: Metronidazole gel is considerably less effective (<50%) than oral preparations and should not be used for trichomoniasis 1

5. Untreated infections: Without treatment, infections can persist for months or longer 7

6. Reinfection vs. treatment failure: Important to distinguish between treatment failure and reinfection when symptoms persist 7