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Trichomonas vaginalis

Reviewer: Farnaz Hasteh, M.D., UCSD Medical Center (see Reviewers page)
Revised: 5 May 2014, last major update March 2011
Copyright: (c) 2006-2012, PathologyOutlines.com, Inc.


● Facultative anaerobic protozoan parasite without mitochondria or peroxisomes
● Morphologic identification with liquid based preparations is highly accurate and should not require confirmatory testing (Diagn Cytopathol 2005;32:341, Am J Obstet Gynecol 2003;188:354); in contrast, confirmatory tested is recommended for diagnosis based on conventional smears of women without symptoms (Obstet Gynecol 1993;82:425)


● Most common sexually transmitted disease worldwide; having multiple sexual partners is a risk factor
● Mainly affects women ages 16-35 years, but can occur in postmenopausal women
● Also affects men, causing urethritis or prostatitis

Clinical features

● More common in ectocervical than endocervical smears (Diagn Cytopathol 1996;14:273)
● Cervix appears strawberry colored due to inflammation
● Frothy, green to white vaginal discharge with strong odor, itching and discomfort
● Sometimes asymptomatic
● In pregnancy, can cause premature rupture of membranes


● Women often receive treatment for positive pap smear, even if asymptomatic (Diagn Cytopathol 2001;24:195)
● Metronidazole (Flagyl) is common treatment; it is reduced inside the parasite by hydrogenase, reacts with oxygen to form radicals that rapidly kill the parasite
● Sexual partner must also be treated

Cytology description

● Pear-shaped, oval to round or kite shaped, 15-30 microns
● Often has eosinophilic cytoplasmic granules
● Pale, vesicular and centrally located nuclei
● Adjacent squamous cells have hyperchromatic nuclei and small, evenly circumscribed, perinuclear halos
● Commonly associated with acute inflammation (polyballs), lymphocytes and even mast cells (DeMay: The Pap Test: Exfoliative Gynecologic Cytology; 2005)
● May coexist with SIL and even cancer
● May coexistent with Leptothrix (long filamentous bacteria)
Note: Cytologic changes may mimic ASCUS or LSIL due to pseudomaturation of squamous cells, perinuclear halo and atypical parakeratosis
● In liquid based cytologic, organisms are smaller but flagella can be seen; however, red granules may be less obvious

Cytology images


Various images

Contributed by Dr. Marilin Rosa, University of Florida (USA)


Electron microscopy images

Differential diagnosis

● Cell fragments, neutrophils, debris, mucus

End of Cervix-cytology > Inflammation/parasites > Trichomonas vaginalis

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