September 29, 2011

Trichomonas vaginalis is the cause of vaginitis.

Trichomonads are motile, flagellate, protozoan organisms known to cause a diverse spectrum of diseases in humans. Most of these diseases are rare. The single exception is Trichomonas vaginalis, the most significant of these parasites, which infects between 3 and 5 million American women each year. The organism causes an inflammation of the vaginal wall, or vaginitis, in women who contract this disease. The disease is usually sexually transmitted and the incidence is high particularly in populations at risk for other venereal diseases, such as those attending clinics for sexually transmitted diseases, those with multiple sexual partners, and those infected with HIV. T. vaginalis also causes genital infections in men; because these tend to be asymptomatic, the true incidence of infection in this population is unknown.

The clinical presentation of trichomoniasis is variable. It is estimated that between one fourth and one half of infected women are asymptomatic; in symptomatic women, the most common complaints are usually of malodorous vaginal discharge, discomfort with urination, and vulvovaginal irritation, pain, or burning. A history of unprotected sexual intercourse is usually present. on pelvic examination, a yellow-green discharge, usually described as “frothy,” may be present in the vagina. other signs may include vulvovaginal erythema (redness) and a “strawberry” appearance of the cervix. The latter finding is caused by microscopic hemorrhages in the surface tissue in the cervix (exocervical mucosa). In men, T. vaginalis infection is usually asymptomatic. Symptomatic men may experience urethral burning, pain with urination, or rarely a penile discharge.

Diagnosis of infection with T. vaginalis in women is usually made by examination of vaginal secretions. Characteristics that are suggestive of trichomoniasis include a yellow-green, frothy discharge, with pH level (acid level) of greater than 4.5. Conclusive proof of disease includes the microscopic identification of the organisms on a wet-mount slide of vaginal secretions. The diagnosis can also be made if the organism is identified in samples recovered from the exocervix (such as those obtained via Pap smear); however, this method is less sensitive and is therefore not currently recommended. In men, a diagnosis of trichomoniasis may be more difficult to establish and microscopic examination of both a urethral sample and a urine sample may be necessary. In both sexes, the ability to detect the disease may be increased by combining direct microscopic evaluation with cultures of infected material. Most importantly, women with trichomoniasis should also be screened for other coexistent sexually transmitted diseases.

Treatment of trichomoniasis is fairly straightforward and, in most cases, exceedingly successful. The mainstay of therapy is the antibiotic metronidazole, which is highly active against most strains of T. vaginalis. The drug can be administered as a single, oral dose (usual dose 2 g) to cure the majority of cases of tri-chomoniasis. This single-dose regimen tends to be easier for most individuals to take. For individuals unable to tolerate this dose or for those with recurrent disease after the single-dose regimen, a 7-day course of therapy, consisting of a gram of metronidazole daily, administered in two divided doses, is recommended. In rare cases of true antibiotic resistance in the organism, higher dose metronidazole, topical paromomycin, and tinidazole have all been shown to be efficacious in eradicating the disease. All infected women should be counseled regarding the necessity of having their sexual partners seek treatment, as reinfection from an asymptomatic sexual partner (partner with no symptoms) remains a common cause of relapsing disease after treatment. Reinforcement of safe sex practices remains critical.

It is generally recommended that all individuals diagnosed with T. vaginalis infection undergo antibiotic treatment. Although many men and some women are diagnosed while asymptomatic, they may become symptomatic at a later date or may unknowingly transmit the organism to others through unprotected sexual contact. Additionally, some studies have suggested that women with untreated trichomoniasis may be more susceptible to HIV disease, due to the damage of surface tissue (disruption of native mucosal barriers) by inflammation. Pregnant women who contract T. vaginalis may be more likely to deliver premature or low-birthweight infants. Although it has not been established conclusively that cure of infection in expectant mothers will prevent these negative events, current guidelines also support treatment of women with trichomoniasis during pregnancy (gestational trichomoniasis).

See Also: Condoms, Safer sex, Sexually transmitted diseases

Suggested Reading

  • Centers for Disease Control and Prevention, Division of Parasitic Diseases. (1999). Parasitic disease information, Trichomonas infection. Atlanta. Retrieved October 15 from
  • Paavonen, J., & Stamm, W. E. (1987). Lower genital tract infections in women. Infectious Diseases Clinics of North America, 1(1), 179—198.
  • Schwebke, J. R. (2002). Update of trichomoniasis. Sexually Transmitted Infections, 78, 378-379.


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