Trichomonas vaginalis Life Cycle: Transmission, Morphology & Clinical Impact

Trichomonas vaginalis is a flagellated protozoan parasite causing trichomoniasis, the most common non-viral STI worldwide. It exists only as a trophozoite—no cyst form in humans.

Life Cycle Stages

1. Trophozoite (only stage in human): Pear-shaped, 10–20 µm, 4 anterior flagella + 1 recurrent flagellum (undulating membrane), axostyle. Motile ("twitching") on wet mount.
2. Binary fission: Asexual replication in vaginal/urethral mucosa; optimal pH 5.5–6.5.
3. Adhesion & cytopathicity: Binds vaginal epithelial cells via adhesins (AP65, AP51, AP33, AP23); secretes proteases, pore-forming proteins → inflammation, microhemorrhages ("strawberry cervix").
4. Transmission: Sexual contact (penile-vaginal, vaginal-vaginal). Fomite transmission theoretically possible (moist towels, shared toys) but rare—trophozoites die quickly when dry.
5. No true cyst: Pseudocysts (rounded, non-motile forms) may appear under stress (pH shift, immune attack) but are not environmentally resistant.

Clinical Features

• Women: frothy yellow-green discharge, vulvar itching, dysuria, strawberry cervix (colposcopy). 50% asymptomatic.
• Men: usually asymptomatic; can cause urethritis, prostatitis, epididymitis.

Diagnosis

• NAAT (PCR/TMA) on vaginal/urine swab — gold standard (sensitivity >95%).
• Wet mount (saline) — sensitivity 50–70%; motility diagnostic.
• Culture (InPouch TV) — 70–80%; 24–48h.
• Rapid antigen test — lower sensitivity.

Treatment

• Metronidazole 2 g single dose (or 500 mg BID × 7 days) — both partners simultaneously.
• Tinidazole 2 g single dose — alternative.
• Abstain from sex until both cured and asymptomatic (~1 week).
• Re-test at 3 months (high reinfection rate).

Trichomoniasis increases HIV acquisition/transmission risk and adverse pregnancy outcomes (PTB, LBW). Screening recommended for high-prevalence populations.