Trichomonas vaginalis is a flagellated protozoa that causes the STI known as trichomoniasis. Trichomoniasis is the most common non-viral STI worldwide and affects both men and women. Trichomonas itself is curable but if untreated it increases the risk of certain complications such as cervical cancer, HIV, PID and pregnancy complications.
It is characterised by four flagella at the anterior end and a single flagellum at the posterior end. These flagella allow trichomonas to be highly motile as well as aid attachment to cells.
Pathophysiology
Trichomonas is transmitted through unprotected vaginal sexual intercourse (it does not pass through oral or anal sex). Its trophozoite form (the protozoa in its feeding stage) remains in the lower genital tract in females and the urethra/prostate in men. Vertical transmission is rare but is still possible during labour. There is a period of incubation lasting approximately 7 days.
It then replicates through binary fission. It destroys epithelial cells by direct cellular contact and the release of cytotoxic substances. It binds to plasma proteins which prevents it from being detected by the complement pathway.
Trichomonas is associated with increased rates of HIV acquisition through mechanisms which are not entirely understood. Some theories are:
- Trichomoniasis results in punctate mucosal haemorrhages which compromises the barrier to HIV infection.
- Leukocyte protease inhibitors that prevent HIV binding to cells are degraded, thus increasing cellular binding by HIV.
- There is increased risk of acquisition by increasing susceptibility to bacterial vaginosis and through persistence of abnormal vaginal flora (as an abnormal vaginal pH may inhibit CD4 lymphocyte activation).
⚠️ Risk factors
- Unprotected sexual intercourse
- Multiple sexual partners
- History of STIs
- Older women
😷 Presentation
Up to 50% of women are asymptomatic. In those that do have symptoms, they may include:
- Vaginal discharge - this occurs in about 50% of women. The consistency of the discharge varies from thin and scanty to profuse and thick. It is typically frothy and yellow-green in appearance.
- Vulval itching
- Dysuria
- Offensive odour
- On examination we may see a strawberry cervix (colpitis macularis) which indicates punctate macular haemorrhages of the cervix. It is a specific sign for trichomoniasis.
It may also lead to less common symptoms of vulval pain, ulceration or even lower abdominal pain.
Approximately 15-50% of men are asymptomatic as well. It is usually that men present as the sexual partner of an infected woman.
Symptoms include:
- Urethral discharge - it is usually in small or moderate amounts but rarely there may be complaints of copious purulent urethral discharge.
- Urethral irritation
- Urinary frequency
- Dysuria
- Dyspareunia
- Balanitis and sometimes even prostatitis.
🔍 Investigations
Suspected trichomoniasis requires referral to GUM clinic for confirmation of the diagnosis.
- Speculum examination - to visualise the cervix and vagina to look for characteristic signs such as a yellow-green, frothy discharge and fishy odour. There may also be signs of cervicitis such as a strawberry appearance.
- Vaginal pH testing - a pH of >4.5 will be present (similar to bacterial vaginosis). The normal vaginal pH in a woman of child-bearing potential is 3.5-4.5.
- High vaginal swab and STI screening - to exclude other causes.
- Urethral swab and/or first-void urine for microscopy and culture.
- STI screening
🧰 Management
Treatment should ideally be provided by the GUM clinic, but if not possible it may be done in primary care.
- Educate the patient and advise sexual abstinence for at least one week.
- Metronidazole - given as a 5-7 day course of 400-500mg BD taken orally or a 2g single dose. However, the 2g single dose is not advised in pregnant or breastfeeding women as it may alter the taste of breast milk. Patients with HIV should complete a 7 day course.
- Treat all partner(s) within the 4-week period prior to presentation.
Patients should be followed up after treatment to review their symptoms and assess further treatment if needed, to confirm that contact tracing has been done, and to discuss the results of the STI screen.
🚨 Complications
🤦♀️ Complications in women:
- HIV transmission is facilitated
- Pelvic inflammatory disease
- Bacterial vaginosis
- Cervical cancer and increased risk of HPV
- Infertility
- Pregnancy complications such as:
- Low birthweight infant
- Preterm delivery
- Maternal postpartum sepsis
🤦♂️ Complications in men:
- HIV transmission is facilitated
- Prostatitis
- Prostate cancer
- Infertility