Trichomonas

Trichomonas vaginalis

Trichomonas vaginalis (T. vaginalis) is a protozoan pathogen that causes trichomoniasis, a sexually transmitted disease primarily of women. Trichomonas produces vaginitis with symptoms of pain, discharge, and dysuria. Infection of men is usually asymptomatic but may cause urethritis, prostatitis or epididymitis. Symptoms fluctuate in intensity, but may persist for weeks or months and usually worsen during menses and pregnancy. Trichomoniasis may increase the risk of preterm birth. Over 3 million women in the United States and 180 million worldwide are infected annually. The peak incidence of trichomoniasis is between 16 and 35 years of age. Although there is evidence of an immune response to T. vaginalis in infected women, there is minimal clinically significant immunity to this pathogen and thus, reinfection can occur.

Transmission

The likelihood of acquiring T. vaginalis is directly related to the number of sexual contacts and non-venereal transmission is uncommon. However, transfer of organisms on shared washcloths may explain the high frequency of infection seen among institutionalized women.

Prevention

There is no vaccine available for T. vaginalis. Treatment of sexual partners of infected women can reduce the problem of reinfection.

Diagnosis

Diagnostic testing is recommended for all women presenting symptoms of vaginitis. The diagnosis of trichomoniasis traditionally was based on morphologic identification of the organism in a wet mount preparation of a swab from vaginal discharge fluid in women or urethral exudate in men. Microscopic evaluation of wet mounts has a positive predictive value negative predictive value of only 60% which can be increased to over 80% with direct immunofluorescent antibody staining. Parasitic culture, though more sensitive, requires several days to complete and is infrequently done. A rapid diagnostic point-of-care dipstick test is available and has reasonably high sensitivity and very high specificity. Molecular diagnostic methods based on PCR have recently become available and offer high sensitivity and specificity.

Treatment

Therapy with oral metronidazole is highly effective for Trichomonas infections. Metronidazol may be given as a single dose or over 7 days. Treatment of sexual partners is recommended to reduce reinfection rates. Metronidazole has a disulfiram-like reaction; therefore, alcohol should be avoided during treatment. The potential teratogenic activity of metronidazole precludes its use during the first trimester of pregnancy.

Recommended Reading

The Color Atlas of Family Medicine, 2e. Chapter 84. Trichomonas vaginalis. Richard P. Usatine, Mindy A. Smith, Heidi S. Chumley, E.J. Mayeaux Jr.

Meites, E.  Trichomoniasis: the "neglected" sexually transmitted disease. Infect Dis Clinic North Am. 2013 Dec;27(4):755-64.

Sutton M, Sternberg M, Koumans EH, et al. The prevalence of Trichomonas vaginalis infection among reproductive-age women in the United States, 2001–2004. Clin Infect Dis 2007;45(10):1319–26.