Question
Trichomonas vaginalis
Answer
Trichomonas vaginalis is a flagellated protozoan parasite, the causative agent of trichomoniasis, one of the most common non-viral sexually transmitted infections worldwide, existing only as a motile trophozoite (no cyst stage), which is directly responsible for both transmission and pathogenicity.
Morphology: pear-shaped trophozoite, typically 10–20 μm, with four anterior flagella, an undulating membrane running along part of its body length (used for characteristic jerky/tumbling motility, visible on wet-mount microscopy), and a prominent axostyle (a rigid rod-like structure running through the cell, protruding posteriorly).
Transmission: almost exclusively sexual contact; can also rarely be transmitted perinatally (mother to infant during vaginal delivery), or, theoretically, via fomites, though this is epidemiologically much less significant given the organism’s fragility outside the host.
Clinical features:
- In women — vaginitis with a characteristic profuse, frothy, yellow-green, malodorous vaginal discharge, vulvovaginal itching/irritation, dysuria, and dyspareunia; on speculum examination, the cervix can show a characteristic “strawberry cervix” appearance (punctate haemorrhages) in a minority of cases.
- In men — often asymptomatic (an important epidemiological point, since asymptomatic male carriers serve as a significant reservoir for continued transmission), or can cause mild urethritis.
Laboratory diagnosis:
- Wet mount microscopy — direct examination of vaginal/urethral discharge for motile trophozoites with characteristic jerky movement — rapid, low-cost, but only moderately sensitive, and requires prompt examination since motility is quickly lost outside the body.
- Culture (e.g., Diamond’s medium) — more sensitive than wet mount but slower.
- Nucleic acid amplification test (NAAT/PCR) — the most sensitive method, increasingly the preferred diagnostic standard.
- Rapid antigen tests — available as point-of-care alternatives with reasonable sensitivity/specificity.
Treatment: metronidazole (or tinidazole) — a single oral dose is standard therapy; treatment of sexual partners is essential to prevent reinfection/continued transmission, and screening for other concurrent STIs is recommended given shared risk factors.