Definition – Trichomonas vaginalis is a flagellated protozoan that causes trichomoniasis, a common sexually transmitted infection
Causative agent – single‑celled protozoan, genus Trichomonas, species vaginalis (only human pathogenic species)
Morphology –
• size 10–20 µm long, 5–15 µm wide
• oval/pear‑shaped body
• four anterior flagella + one posterior flagellum forming an undulating membrane
• axostyle (supporting rod) runs through the cell
• nucleus centrally placed, multiple hydrogenosomes (energy organelles)
Life cycle (only trophozoite stage) –
- Trophozoite enters genital tract during sexual contact → adheres to mucosal epithelium
- Feeds on bacteria and epithelial cells for nutrients
- Reproduces asexually by binary fission (≈6‑12 h generation time)
- Remains viable only in moist, anaerobic environment of vagina, urethra, cervix (female) or urethra (male)
- Dies rapidly outside the host (no cyst formation)
Pathogenesis –
→ Adherence: surface lectin‑like proteins bind to vaginal epithelial glycoconjugates
- Attachment damages microvilli and disrupts epithelial barrier
- Cytotoxic metabolites (hydrogen peroxide, proteases) cause cell lysis and inflammation
- Local immune response → neutrophil influx, cytokine release, increased vaginal discharge
- Chronic inflammation may ascend → pelvic inflammatory disease, increased susceptibility to HIV and other STIs
Clinical features –
Female: frothy yellow‑green discharge, itching, burning, dysuria, dyspareunia, sometimes asymptomatic
Male: urethral discharge (clear or mucoid), burning on urination, mild prostatitis, often asymptomatic
Complications –
• Pelvic inflammatory disease, infertility, ectopic pregnancy
• Pre‑term labor, low birth weight in pregnant women
• Enhanced transmission/acquisition of HIV and other STIs
• Possible association with cervical cancer (controversial)
Diagnosis –
• Wet mount of vaginal/urethral discharge: motile trophozoites seen within minutes
• Culture in Diamond’s medium (sensitive, for research)
• Nucleic acid amplification test (NAAT) – most sensitive, can be done on urine or swab
• Antigen detection kits (rapid)
Management –
• Metronidazole 2 g single oral dose or 500 mg twice daily for 7 days (preferred)
• Tinidazole 2 g single dose (alternative, better taste)
• Treat sexual partner(s) simultaneously to prevent reinfection
• Advise abstinence for 7 days after therapy, use condoms thereafter
• In pregnancy: metronidazole 2 g single dose is safe; avoid tinidazole in first trimester
Memory trick – Life cycle: “Trophozoite Hangs, Feeds, Splits, Stays, Dies” (T H F S S D) – reminds that only the trophozoite lives, feeds, multiplies, stays in moist sites and dies outside.
Pathogenesis trick – “Attach → Damage → Inflammation → Complications” (A D I C) – easy rhyme to recall the four steps.