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Laboratory diagnosis of Trichomonas vaginalis infections

Trichomonas vaginalis is a protozoan parasite. It causes trichomoniasis; a sexually transmitted infection. The primary habitat of this organism is vagina and prostate.
In infected female it causes itching and burning accompanied by profuse, foul-smelling, yellow- green vaginal discharge (about 25% women are symptomatic). Infected male are generally asymptomatic, some (about 10%) may develop urethritis. It is not possible to diagnose trichomoniasis based on these symptoms alone.

Note: Trichomonas vaginalis is not exclusive parasite of women, it also infects men.

Life cycle of Trichomonas vaginalis (image source: CDC)

Sample:  Specimen can be collected by using urogenital swabs.

  1. Female: Urine sediment, vaginal secretions
  2. Male: Urethral discharge or prostate secretions or first few drops of voided urine

Sample for culture should be placed into a tube containing 0.5mL of sterile saline or commercially available plastic envelops for direct examination and culture (InPouch TV, BIOMED) immediately.

Methods:

  1. Microscopy and staining:
    Trophozoite of Trichomonas vaginalis

    Direct microscopic examination of a wet preparation of sample (vaginal discharge) provides the simplest rapid diagnostic test for vaginalis.  It includes detection of pear shaped trophozoites (only form; there is no cyst form) of T. vaginalis in wet mount with typical jerky motility. Direct fluorescent Antibody (DFA) stain can be used to visualize the parasite.

    Morphological features of Trophozoites: 
    1. Pear shaped organism with a central nucleus and four anterior flagella.
    2. It has an undulating membrane that extends about 2/3rd of its length.

    (Watch the video of vaginal discharge observed under Phase Contrast Microscopy here)

  2. Culture: Culture is very sensitive (95%) procedure for diagnosis of trichomoniasis. It is recommended when direct smear is negative. Johnson’s and Trussel’s medium gives a good growth of T. vaginalis. It consists of proteose peptone, NaCl, Sodiumm thioglycollate and human serum. It grows best at 35°C-37°C anaerobic conditions and less well aerobically.  The optimal pH for growth is 5.5 to 6.0.  T. vaginalis can be cultured in commercially available Diamond’s medium or plastic envelopes.
  3. Serology: Better serologic test for T. vaginalis is not available.
  4. Molecular Methods: Polymerase chain reactions (PCR) and nucleic acid hybridization method can be used to detect T.vaginalis directly in clinical specimens.