Trichomonas vaginalis

Trichomonas vaginalis is a parasite that can infect the urogenital systems of both men and women. It was initially discovered by Donne in 1836. The pathogenic parasite T. vaginalis causes vaginitis, urethritis, and prostatitis. T. vaginalis infection is frequently mistaken for a sexually transmitted disease. Freshly voided urine, prostatic secretions, and vaginal wet preparations from both sexes may include the motile trophozoite.

In most cases, the motile trophozoite, a pear-shaped, elongated structure detected in fresh urine and urogenital specimens, is employed to make the diagnosis. The parasites move jerkily and undulatingly and are about the size of a neutrophil.

Habitat and Morphology

T. vaginalis can be present in the female vagina and cervix, as well as the Bartholin’s glands, urethra, and urinary bladder. It often affects men’s anterior urethra, but it may also affect the prostate and preputial sac.

Trichomonas vaginalis trophozoite

T. vaginalis only exists as a trophozoite; trichomonas has no cystic form. The trophozoite is ovoid or pear-shaped, with a short undulating membrane extending up to the middle of the body, and is around 10 to 30 µm long and 5 to 10 µm wide.

  • It has four anterior flagella and a fifth that runs along the outer edge of the undulating membrane, which is protected at its base by the costa, a flexible rod.
  • A prominent axostyle runs throughout the length of the body and projects posteriorly.
  • The cytoplasm has a lot of granules, particularly near the axostyle and costa.
  • It is motile and moves in a jerky or twitching manner.

Life Cycle of T. vaginalis

T. vaginalis completes its life cycle in a single host, whether male or female. Since the trophozoite can’t live outside, infection must be passed from person to person. The most common mode of infection is by sexual contact. Trichomoniasis also occurs in the presence of other sexually transmitted diseases such as candidiasis, gonorrhea, syphilis, or the human immunodeficiency virus (HIV).

T. vaginalis trophozoites live on the mucosal surface of untreated women’s vaginal mucosa. The trophozoites feed on local bacteria and leukocytes and reproduce by linear binary fission. The trophozoites of T. vaginalis grow in a slightly alkaline or slightly acidic pH state, such as that found in an unhealthy vagina. In males, the prostate gland area and the urethral epithelium are the most prominent  T. vaginalis infection sites. The male host’s complete life cycle is unclear.

Pathogenesis of T. vaginalis

T. vaginalis prefers to infect squamous epithelia rather than columnar epithelia. Cysteine proteases, lactic acid, and acetic acid are secreted, which disrupt glycogen levels and lower the pH in the vaginal fluid. T. vaginalis is an obligate parasite that requires direct contact with the vaginal, urethral, or prostatic tissues to survive. The parasite induces petechial hemorrhage, metaplastic alterations, and vaginal epithelium desquamation. The most common symptom of trichomoniasis is intracellular edema, also known as chicken-like epithelium.

Clinical features of Trichomoniasis

Although some people develop urethritis, epididymitis, or prostatitis, infection is mostly asymptomatic, particularly in men. It may cause serious pruritic vaginitis in women, accompanied by an offensive yellowish-green frothy discharge, dysuria, and dyspareunia. Erosion of the cervical spine is a natural occurrence. Complications such as endometritis and pyosalpingitis are rare. Trichomoniasis has a 4 days to a month incubation cycle.

Persistent Urethritis

The disease that symptomatic men develop as a result of a T. vaginalis infection is persistent or chronic urethritis. In extreme cases of infection, the seminal vesicles, higher parts of the urogenital tract, and the prostate can be affected. A swollen tender prostate, dysuria, nocturia, and epididymitis are also signs of a major infection.

Persistent Vaginitis

After a 4 to 28-day incubation cycle, persistent vaginitis causes a foul-smelling, greenish-yellow liquid vaginal discharge in infected women. The exacerbation of symptoms is more likely due to vaginal acidity present before and shortly after menstruation. There might even be burning, scratching, and chafing. Examining the vaginal mucosa of infected women can reveal red punctate lesions. The most frequent symptoms include urethral involvement, dysuria, and elevated frequency of urination. Cystitis is less common.

Infant Infections

T. vaginalis has been found in children with respiratory infections as well as conjunctivitis. T. vaginalis trophozoites migrates from an infectious mother to the child via the birth canal and/or during vaginal delivery.

Laboratory Diagnosis

Microscopic examination

  • Microscopically, vaginal or urethral discharge is inspected for typical jerky and twitching motility and structure in a saline wet mount preparation. Males may have trophozoites in their urine or prostatic secretions.
  • Fixed smears may be stained with acridine orange, papanicolaou, and Giemsa stains.
  • Another way of parasite identification is direct fluorescence antibody (DFA), which is more sensitive than wet mount.


Under anaerobic conditions, it grows better at 35°–37°C. A pH of 5.5–6.0 is ideal for growth. It can be grown in a combination of solid and liquid media, tissue culture, and eggs, among other things. Plastic envelope medium (PEM) and cystein­peptone­liver­maltose (CPLM) medium are commonly used.

Treatment of Trichomoniasis

Metronidazole is the drug of choice for T. vaginalis infections, with a few exceptions. Since this parasite is transmitted via sexual contact, it is important that all sexual partners be treated.


  1. Textbook of Medical Parasitology
  2. Clinical Parasitology A practical Approach 2nd Edition

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