Trichomonas vaginalis

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Template:Taxobox name
Scientific classification
Domain: Eukaryota
(unranked) Excavata
Phylum: Metamonada
Class: Parabasalia
Order: Trichomonadida
Genus: Trichomonas
Species: T. vaginalis
Binomial name
Trichomonas vaginalis
(Donné 1836)
This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see trichomoniasis.

For patient information click here

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]


Trichomonas vaginalis, an anaerobic, parasitic flagellated protozoan, is the causative agent of trichomoniasis, and is the most common pathogenic protozoan infection of humans in industrialized countries.[1] The WHO has estimated that 180 million infections are acquired annually worldwide. The estimates for North America alone are between 5 and 8 million new infections each year, with an estimated rate of asymptomatic cases as high as 50%.[2]

Protein function

T. vaginalis also has many enzymes that catalyze a number of reactions making the organism relevant to the study of protein function. T. vaginalis lacks mitochondria and other necessary enzymes and cytochromes to conduct oxidative phosphorylation. T. vaginalis obtains nutrients by transport through the cell membrane and by phagocytosis. The organism is able to maintain energy requirements by the use of a small amount of enzymes to provide energy via glycolysis of glucose to glycerol and succinate in the cytoplasm, followed by further conversion of pyruvate and malate to hydrogen and acetate in an organelle called the hydrogenosome.[3]


The T. vaginalis trophozoite is oval as well as flagellated. Five flagella arise near the cytosome; four of these immediately extend outside the cell together, while the fifth flagellum wraps backwards along the surface of the organism. The functionality of the fifth flagellum is not known. In addition, a conspicuous barb-like axostyle projects opposite the four-flagella bundle; the axostyle may be used for attachment to surfaces and may also cause the tissue damage noted in trichomoniasis infections.[4]

While T. vaginalis does not have a cyst form, organisms can survive for up to 24 hours in urine, semen, or even water samples. Combined with an ability to persist on fomites with a moist surface for 1 to 2 hours, T. vaginalis is among the most durable protozoan trophozites.


File:Pap test trichomonas.JPG
Pap smear, showing infestation by Trichomonas vaginalis. Papanicolau stain, 400x.

Trichomoniasis can occur in females (males rarely exhibit any symptoms of a T. vaginalis infection) if the normal acidity of the vagina is shifted from a healthy, semi-acidic pH (3.8 - 4.2) to a much more basic one (5 - 6) that is conducive to T. vaginalis growth. Some of the symptoms of T. vaginalis include: preterm delivery, low birth weight, and increased mortality as well as predisposing to HIV infection, AIDS, and cervical cancer.[5] T. vaginalis has also been reported in the urinary tract, fallopian tubes, and pelvis and can cause pneumonia, bronchitis, and oral lesions. Other symptoms include inflammation with increasing number of organisms, greenish-yellow frothy vaginal secretions and itching.

T. vaginalis can be detected by studying discharge or with a pap smear and culturing. With a pap smear, infected individuals would have a transparent "halo" around their superficial cell nucleus. T. vaginalis is diagnosed via a wet mount, in which "corkscrew" motility can be observed. Condoms are effective at preventing infection.

Metronidazole or tinidazole can treat an infection in progress, and should be prescribed to sexual partners as well.[6].

Genome Sequencing

Jane Carlton led a project to sequence the Trichomonas vaginalis genome which found that the genome was much larger than was expected.[2] [3]


  1. Soper D (2004). "Trichomoniasis: under control or undercontrolled?". Am J Obstet Gynecol. 190 (1): 281–90. PMID 14749674.
  2. Hook E (1999). "Trichomonas vaginalis--no longer a minor STD". Sex Transm Dis. 26 (7): 388–9. PMID 10458631.
  3. Upcroft P, Upcroft J (2001). "Drug targets and mechanisms of resistance in the anaerobic protozoa". Clin Microbiol Rev. 14 (1): 150–64. PMID 11148007.
  4. Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0838585299.
  5. Schwebke J, Burgess D (2004). "Trichomoniasis". Clin Microbiol Rev. 17 (4): 794–803, table of contents. PMID 15489349.
  6. Cudmore S, Delgaty K, Hayward-McClelland S, Petrin D, Garber G (2004). "Treatment of infections caused by metronidazole-resistant Trichomonas vaginalis". Clin Microbiol Rev. 17 (4): 783–93, table of contents. PMID 15489348.

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