Trichomonas vaginalis

What is trichomonas vaginalis?

Trichomonas vaginalis (TV) is a very common sexually transmitted infection (STI) that can cause vaginitis, cervicitis and urethritis.

Trichomonas vaginalis causes

• Trichomonas vaginalis is a flagellated protozoan.

• Trichomonas vaginalis is a member of the Parabasalia, a group of single-celled eukaryotes within the clade Excavata, which also includes parasites of genera such as Giardia and Trypanosoma¹ .

• In women the organism is found in the vagina, urethra and paraurethral glands.

• Urethral infection is present in 90% of infected women² .

• In men infection is usually of the urethra.

• In adults transmission is almost exclusively through sexual intercourse.

Epidemiology³

• Trichomonas vaginalis is the most common curable STI worldwide. The World Health Organization (WHO) estimated 156 million cases of T. vaginalis worldwide in 2016, accounting for almost half of the global STI incidence that year.

• T. vaginalis prevalence was 1.8% in women and 0.5% in men aged 18-59 years in the USA in 2018.

• Despite having the highest prevalence of any STI globally, there is a dearth of data describing Trichomonas vaginalis incidence and prevalence in the general population .

• Trichomonas vaginalis is still underdiagnosed and therefore undertreated.

Trichomonas vaginalis symptoms

Women

• The symptoms of Trichomonas vaginalis can be confused with bacterial vaginosis (BV).

• Around 70% of women have a vaginal discharge.

• Although this is usually a frothy yellowish discharge, it can vary from being thin and scanty to profuse and thick.

• Other common symptoms include vulval itching, dysuria or offensive odour.

• Lower abdominal discomfort can occur in some women.

• There may be signs of local inflammation with vulvitis and vaginitis.

• Cervicitis may be present which leads to the cervix having the appearance of the surface of a strawberry; sometimes referred to a 'strawberry cervix'.

• 10-50% of women will have no symptoms and 5-15% of women will have a normal examination² .

Men

• Men are usually asymptomatic.

• Trichomonas vaginalis is increasingly being recognised as a cause of non-gonococcal urethritis⁴ .

• The most common symptoms are dysuria and presence of a urethral discharge.

• The vast majority of men will have no abnormal signs on examination.

Differential diagnosis

• Other vaginal infections - eg, candidiasis, BV, chlamydia, gonorrhoea, herpes simplex.

• Other benign causes of vaginal discharge - eg, physiological discharge, chemical irritants, foreign body, pregnancy, cervical ectropion.

• Postmenopausal vaginal discharge due to atrophic vaginitis.

• Vaginal discharge after gynaecological surgery.

• Other causes of prostatitis, cervicitis and cystitis.

Investigations

• If Trichomonas vaginalis is suspected, a high vaginal swab can be taken from the posterior fornix but sensitivity may be low because motility reduces with transit time.

• Self-administered vaginal swabs are increasingly being performed.

• Referral to a genitourinary clinic is therefore recommended for confirmation by wet microscopy which should be read within 10 minutes of collection⁵ .

• Laboratories may not routinely perform wet microscopy or Trichomonas vaginalis culture so suspected Trichomonas vaginalis should be mentioned on the laboratory request form.

• Women with suspected Trichomonas vaginalis should also have contact tracing undertaken.

• Women with Trichomonas vaginalis need testing for other STIs.

• Urethral culture or culture of first-void urine will diagnose 60-80% of cases in men.

• Test of cure is only recommended if symptoms persist or recur.

• Screening of asymptomatic people (including those who are pregnant) is currently not recommended.

• Nucleic acid amplification tests (NAATs) offer the highest sensitivity for the detection of Trichomonas vaginalis. They should be the test of choice where resources allow and are becoming the current gold standard² .

Trichomonas vaginalis treatment^{2 6}

• Both partners should ideally be treated at the same time.

• Sexual intercourse should be avoided for at least one week following receiving treatment.

• All patients should receive clear and accurate written information about this condition.

• Although TV is easily treated with metronidazole in most cases, resistant strains are on the increase⁷ .

• Systemic treatments are far more effective than topical treatments and include:

  • Oral metronidazole 2 g as a single dose.

  • Oral metronidazole 400 mg to 500 mg bd for five to seven days.

  • Oral tinidazole 2 g single dose that can be given as an alternative if metronidazole is not effective.

• Treatment of partners is recommended, regardless of their results.

NB: metronidazole can be used in all stages of pregnancy and during breastfeeding. Although symptomatic women should be treated at diagnosis, some clinicians have preferred to defer treatment until the second trimester. High-dose regimens are not recommended to be taken during pregnancy. The manufacturers recommend avoiding high doses if breastfeeding or, if using a single dose of metronidazole, breastfeeding should be discontinued for 12-24 hours to reduce infant exposure. Tinidazole should be avoided during pregnancy.

Complications

Complications of Trichomonas vaginalis include:

• Preterm delivery and low birth weight⁸ .

• Trichomonas vaginalis infection at delivery may predispose to maternal postpartum sepsis.

• There is evidence that trichomoniasis infection enhances HIV acquisition⁹ .

• Persistent and recurrent Trichomonas vaginalis infections are frequent in women, potentially due to the lack of routine screening recommendations for this pathogen, the chronic nature of some infections and also drug resistance¹⁰ .

• Prostatitis can occur in men and studies also suggest a possible role for T. vaginalis in the development of clinically significant prostate cancer¹¹ .

Prognosis

Spontaneous resolution of T. vaginalis is known to occur at relatively high rates (36-69%) in men³ . Patients who are treated with metronidazole have a 90-95% cure rate but recurrent infections are common in sexually active individuals⁶ . The cure rates are even higher when the sexual partner is treated. Trichomoniasis is strongly associated with the presence of other STIs including HIV, gonorrhoea, human papillomavirus (HPV), herpes and chlamydia.