Trichomonas vaginalis is a very common sexually transmitted infection (STI) that can cause vaginitis, cervicitis and urethritis.
- T. vaginalis is a flagellated protozoan.
- T. 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.
- In women the organism is found in the vagina, urethra and paraurethral glands.
- Urethral infection is present in 90% of infected women.
- In men infection is usually of the urethra.
- In adults transmission is almost exclusively through sexual intercourse.
- T. vaginalis is the most common curable STI worldwide.
- Despite having the highest prevalence of any STI globally, there is a dearth of data describing T. vaginalis incidence and prevalence in the general population.
- T. vaginalis is still underdiagnosed and therefore undertreated.
- The symptoms of T. 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 examination.
- Men are usually asymptomatic.
- T. 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, cervicitis and cystitis.
- If T. 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 collection.
- Laboratories may not routinely perform wet microscopy or T. vaginalis culture so suspected T. vaginalis should be mentioned on the laboratory request form.
- Women with suspected T. vaginalis should also have contact tracing undertaken.
- Women with T. 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 T. 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..
- 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 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 breast-feeding. 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 breast-feeding or, if using a single dose of metronidazole, breast-feeding should be discontinued for 12-24 hours to reduce infant exposure. Tinidazole should be avoided during pregnancy.
Complications of T. vaginalis include:
- Preterm delivery and low birth weight.
- T. vaginalis infection at delivery may predispose to maternal postpartum sepsis.
- There is growing evidence that trichomoniasis infection may enhance HIV transmission.
- There may be an increased risk of T. vaginalis infection in those people who are HIV-positive.
- Persistent and recurrent T. 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.
- Prostatitis can occasionally occur in men.
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