Trichomonas vaginalis

What is trichomonas vaginalis?

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

• 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 Trypanosoma.¹

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

• Urethral infection is present in 90% of infected women.²

• In men, infection is usually of the urethra.

• In adults, transmission is almost exclusively through sexual intercourse.

• Trichomonas vaginalis is the most common curable STI worldwide - in 2020, there were around 156 million cases of T. vaginalis worldwide, accounting for almost half of the global STI incidence that year.

• It is less common in the UK, with chlamydia being the most common STI.

• 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 probably underdiagnosed (as asymptomatic people do not seek a diagnosis) and therefore undertreated.

Women ⁵

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

• Up to 50% of women with TV are asymptomatic - of those who have symptoms, 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'.

Men ⁶

• Men are usually asymptomatic.

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

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

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

• 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, urethritis, cervicitis and cystitis.

• 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.

• If symptoms are convincing but swabs taken in general practice are negative, referral to a genitourinary clinic is therefore recommended for confirmation by wet microscopy which should be read within 10 minutes of collection.

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

• 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.

• 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 standard.

• 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 increase. ⁷

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

  • Oral metronidazole 2 g as a single dose (not during pregnancy or breastfeeding).

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

  • Oral tinidazole 2 g single dose could theoretically be given as an alternative if metronidazole is not effective, but is not currently available in the UK.

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

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

Complications of Trichomonas vaginalis include:

Pregnancy related:

• Preterm delivery and low birth weight.

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

Non-pregnancy related:

• There is evidence that trichomoniasis infection enhances HIV acquisition.

• 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 resistance.⁸

• Prostatitis can occur in men and studies also suggest a possible role for T. vaginalis in the development of clinically significant prostate cancer.⁹¹⁰

Up to a third of cases may resolve spontaneously. ¹¹¹² Patients who are treated with metronidazole have a 90-95% cure rate but recurrent infections are common in sexually active individuals.⁶ 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.