Trichomoniasis is a sexually transmitted disease caused by Trichomonas vaginalis in humans, or Tritrichomonas foetus in cattle.

Keywords: Trichomonas vaginalis; sexually transmitted disease; vaginal infection

Figure 1.

Scanning electron micrograph (SEM) of Trichomonas vaginalisin vivo. The parasite attaches to the host epithelial cell (E) via cytoplasmic extensions indicated by the arrow. AF, anterior flagella; RF, recurrent flagellum. Bars, 5 μm. Photographs kindly supplied by Dr M. A. Vannier‐Santos (Universidade Federal do Rio de Janeiro, Brazil).

Figure 2.

Nitroimidazoles used as antitrichomonad agents. (a) Metronidazole was the first nitroimidazole shown to have antimicrobial activity, and to date is the only drug approved in the USA for treatment of human trichomoniasis. (b) Dimetridazole and (c) ipronidazole are used for the treatment of bovine trichomoniasis. The presence of the nitro group on the 5′ position (bold) of the imidazole ring confers specificity to the drug because of the low redox potential required to activate the nitro group when in this position.

Figure 3.

Pathway of pyruvate metabolism by Trichomonas vaginalis hydrogenosomes. Pyruvate is metabolized to acetate and electrons are shuttled via ferredoxin to protons, forming hydrogen. The high energy bond of acetyl‐coenzyme A (CoA) is used to drive the formation of ATP from ADP. (1) Pyruvate:ferredoxin oxidoreductase. (2) Succinyl‐CoA synthetase. (3) Succinate thiokinase. (4) Adenylate kinase. (5) Hydrogenase. (6) Metronidazole (MTZ) diverts electrons from hydrogenase, inhibiting hydrogen production and undergoing the stepwise reduction to first the nitro‐anion free radical (MTZ*). (7) Three further electrons are sequentially accepted, forming the nitroso, nitroso‐free radical and hydroxylamine (HNOH). (8) Oxygen can oxidize the nitro‐free radical of metronidazole, resulting in futile cycling of the first step of metronidazole reduction.



Augenbraun MH and McCormack WM (1994) Sexually transmitted diseases in HIV‐infected persons. Infectious Diseases Clinics of North America 8: 439–448.

Borchardt KA (1997) Trichomoniasis. In: Honigberg BM (ed.) Trichomonads Parasitic in Humans, pp. 3–35. New York: Springer.

Centers for Disease Control (1982) Sexually transmitted disease treatment guidelines. Morbidity and Mortality Weekly Report 31S: 47S–48S.

Fenoglio CM and Ferenczy A (1982) Etiological factors in cervical neoplasia. Seminars in Oncology 9: 349–371.

Gram IT, Macaluso M, Churchill J and Stalsberg H (1992) Trichomonas vaginalis (TV) and human papilloma virus (HPV) infection and the incidence of cervical intraepithelial neoplasia (CIN) grade III. Cancer Causes and Control 3: 231–236.

Hammill MA (1989) Trichomonas vaginalis. Obstetrics and Gynecology Clinics of North America 16: 531–540.

Jackson DJ, Rakwar JP, Bwayo JJ, Kreiss JK and Moses S (1997) Urethral Trichomonas vaginalis infection and HIV‐1 transmission. Lancet 350: 1076.

Kulda J, Tachezy J and Cerkasovová A (1993) In vitro induced anaerobic resistance to metronidazole in Trichomonas vaginalis. Journal of Eukaryotic Microbiology 40: 262–269.

Kurnatowska A and Komorowska A (1989) Urogenital trichomoniasis in children. In: Honigberg BM (ed.) Trichomonads Parasitic in Humans, pp. 246–273. New York: Springer.

Lloyd D, Yarlett N, Yarlett NC, Pedersen JZ and Kristensen B (1988) Metronidazole‐resistant clinical isolates of Trichomonas vaginalis maintain low intracellular metronidazole radical anion levels as a consequence of defective oxygen scavenging. Acta Universitatis Carolinae, Biologica 30: 521–528.

Lossick JG (1989) Therapy of urogenital trichomoniasis. In: Honigberg BM (ed.) Trichomonads Parasitic in Humans, pp. 324–341. New York: Springer.

Müller M (1993) The hydrogenosome. Journal of General Microbiology 139: 2879–2889.

Yarlett N, Yarlett NC and Lloyd D (1986) Metronidazole resistant clinical isolates of Trichomonas vaginalis have lowered oxygen affinities. Molecular and Biochemical Parasitology 19: 111–116.

Yule A, Skirrow SZ and BonDurant RH (1989) Bovine trichomoniasis. Parasitology Today 5: 373–377.

Further Reading

Alderete JF (1988) Alternating phenotypic expressions of two classes of Trichomonas vaginalis surface markers. Reviews in Infectious Diseases 10: S408–S412.

Beller FK and Schumaker GFB (1979) The Biology of the Fluids of the Female Genital Tract, pp. 1–435. Amsterdam: Elsevier/North Holland.

Goldman P (1980) Metronidazole: proven benefits and potential risks. Johns Hopkins Medical Journal 147: 1–9.

Honigberg BM (1989) Trichomonads Parasitic in Humans, pp. 1–424. New York: Springer.

Petrin D, Delgaty K, Bhatt R and Garber G (1998) Clinical and microbiological aspects of Trichomonas vaginalis. Clinical Microbiology Reviews 11: 300–317.

Rein MF and Müller M (1990) Trichomonas vaginalis and trichomoniasis. In: Holmes KK (ed.) Sexually Transmitted Diseases, pp. 481–492. New York: McGraw‐Hill.

Yarlett N (1988) Polyamine biosynthesis and inhibition in Trichomonas vaginalis. Parasitology Today 4: 357–360.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Yarlett, Nigel(Apr 2001) Trichomoniasis. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001941]