OCCURRENCE: In average populations of developed countries, infection rates are about 5–20% in women and usually below 5% in men.
PARASITE, LIFE CYCLE, AND EPIDEMIOLOGY: Trichomonas vaginalis is a pearshaped protozoon. Five flagella emerge from a basal body at the anterior pole, four freely extend forwards and one extends backwards, forming the outer edge of the undulating membrane, which reaches back only just beyond the middle of the cell. An axial rod made up of microtubules protrudes with its free tip from the posterior end of the cell. The oval cell nucleus lies near the upper pole of the protozoon.
Trichomonads are anaerobic protozoa that possess hydrogenosomes, which are specialized organelles producing H2 as a metabolite. T. vaginalis colonizes the mucosa of the urogenital tract and reproduces by longitudinal binary fission. Trichomonads do not encyst, although rounded, nonmotile forms are observed which are degenerated stages without epidemiological significance. The parasites are transmitted mainly during sexual intercourse. About 2–17% of female neonates born of infected mothers contract a perinatal infection.
SUSCEPTIBILITY TO DRYNESS AND CHEMICALS: T. vaginalis is highly labile outside of a host. Nonetheless, a few trophozoites can survive for up to five hours in the water of non-chlorinated thermal baths and for five minutes to 24 hours in tap water with standard chlorination; they are killed within a few minutes in swimming-pool water with high chlorine concentrations. It is conceivable that infections could be transmitted by wet bathing suits, sponges, towels, etc. as well as acquired from non-chlorinated thermal baths and poorly maintained swimming pools, but there is no evidence showing that these are significant sources of infection.
CLINICAL MANIFESTATIONS: In women, T. vaginalis primarily colonizes the vaginal mucosa, more rarely that of the cervix. In about 20–50% of cases the infection is asymptomatic, but vaginitis can develop after an incubation period of two to 24 days. The infection results in production of a purulent, thin, yellowish discharge in which trichomonads, pus cells, and bacteria are found.
The parasites also enter the urethra in about 75–90% of cases, where they can also cause an inflammation, but only rarely infect the urinary bladder or uterus. Infections in men are for the most part asymptomatic (50–90%), but they may also cause a symptomatic urethritis, more rarely involving the prostate gland and seminal vesicles as well. Infection does not confer effective immunity.
DIAGNOSIS: A fresh specimen of vaginal or urethral secretion is mixed with physiological saline solution and examined under a microscope for trichomonads. The trichomonads are readily recognized by their typical tumbling movements. The round trichomonad forms, by contrast, are hardly distinguishable from leukocytes. Trichomonads can also be identified in smear preparations following Giemsa staining or in an immunofluorescence test with monoclonal antibodies. The most reliable diagnostic results are obtained by culturing specimens in special liquid media. Other special methods are based on detection of antigen (ELISA) or DNA (PCR).
THERAPY AND PREVENTION: It is always necessary for both sexual partners to receive treatment. Effective nitromidazole preparations for oral application in women vaginal application include metronidazole, tinidazole and ornidazole. These substances are contraindicated in early pregnancy. Preventive measures are the same as for other venereal diseases.
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