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Closely related to T. hominis, yet morphologically and physiologically distinct from it, is T. vaginalis (Figs. 3-30 to 3-32).The usual size range of this parasite is apparently 5 to 15 μm, but it may reach a length of 30 μm. In general appearance these flagellates are very similar to T. hominis, from which they differ in having a short undulating membrane that extends only about half the distance to the posterior end of the body, with no free flagellum. The life cycle of T. vaginalis is illustrated in Figure 3-30.

While it is possible to distinguish T. vaginalis from T. hominis on morphologic grounds, this is not a practical necessity, because the two organisms are site specific. Numerous attempts have been made to introduce T. hominis into the vagina, but without success.When T. vaginalis is similarly introduced, a high percentage of infections results. Therefore, a spe-cific identification may be made on the basis of finding a trichomonad in the vaginal secre-tions. Jerky, nondirectional motility characterizes this species, as it does T. hominis, and if the organisms are observed under the high dry power of the microscope, when they have become sufficiently slowed down, the undulating membrane is clearly visible.

Symptoms and Pathogenesis. Trichomoniasis is a common sexually transmitted disease that causes an estimated 2 to 3 million symptomatic infections per year among sexually active women in the United States.Vaginal discharge is the most common complaint asso-ciated with vaginal trichomoniasis. The discharge is frequently profuse and is often associ-ated with burning, itching, or chafing. When viewed through a speculum, the vaginal mucosa is sometimes diffusely hyperemic, with bright red punctate lesions, sometimes only patchily hyperemic and not infrequently normal in appearance. Frequency of urination and dysuria are the commonest associated symptoms, and urethral involvement is found in a

large proportion of cases. Cystitis may occur in a small portion of cases. A relationship between this infection and cervical carcinoma has been suggested.

T. vaginalis also may be an important cofactor in amplifying HIV transmission (Sorvillo et al., 2001). The pathology induced by T. vaginalis infection in a person co-infected with HIV increases HIV shedding. Studies in Africa have indicated that T. vaginalis infection may increase the rate of HIV transmission by approximately twofold.

T. vaginalis has been isolated from the respiratory tract of infants with respiratory disease and from the conjunctivae of several infants with conjunctivitis. Evidence suggests that the infants were infected during vaginal delivery of an infected mother.

In males infection is frequently asymptomatic, but more severe symptoms are likely to be seen when the infection involves the prostate and seminal vesicles or higher parts of the urogenital tract. A thin discharge, frequently containing trichomonads, may be observed, with dysuria and nocturia.The prostate may be enlarged and tender, and there is sometimes associated epididymitis.

Studies in vitro of T. vaginalis with mammalian cell cultures have demonstrated a contact-dependent cytopathic effect. Organisms were able to kill target cells by direct contact without phagocytosis.At least four trichomonad surface proteins have been identified in cell adherence. Additional, T. vaginalis has been shown to produce a cell-detaching factor that causes detachment of cultured mammalian cells and likely the sloughing of vaginal epithelial cells seen in clinical disease.The amount of cell-detaching factor produced by the flagellates

Trophozoite Trophozoite

Trophozoites in urethral and vaginal discharge

No cyst stage Infection acquired by

sexual intercourse

FIGURE 3-30 ■ Life cycle of Trichomonas vaginalis.

appeared to correlate with the severity of the clinical infection and therefore may be a virulence marker in T. vaginalis pathogenesis. Experimental evidence also suggests that the symptoms of trichomoniasis may be influenced by the vaginal concentration of estrogens;

the greater the concentration the less severe the symptoms.β-Estradiol was shown to decrease the activity of cell-detaching factor and may explain why intravaginal estradiol pellets amelio-rate the clinical symptoms of Trichomonas vaginitis by providing high local concentrations of estrogens.

Diagnosis. Diagnosis is by demonstration of the trichomonads, most commonly in wet film preparations although they may readily be recognized in Papanicolaou smears. Specimens for examination may best be obtained through a vaginal speculum using a cotton-tipped applicator stick. If the applicator is placed for a short time in a tube containing a small quantity of 5% glucose in normal saline before examination, the organisms are less likely to be rounded up and motionless under the microscope. Phase-contrast microscopy is espe-cially desirable for observing the flagella and undulating membrane of living T. vaginalis.

10 μ

FIGURE 3-31 ■ Trichomonas vaginalis as seen in permanently stained preparation.

FIGURE 3-32 ■ Scanning electron micrograph of Trichomonas vaginalis from culture. Bar is 10 μm. (Photomicrograph by Dr. Thomas B. Cole, Jr.)

is made by examination of urethral discharge, prostatic secretions, or centrifuged urine.

Culture methods may be employed and sometimes increase the percentage of positive iden-tifications. Of the various commercial culture media available, modified Diamond’s medium (see Chapter 14) consistently supports growth of T. vaginalis.* Modified thioglycolate medium, supplemented with yeast extract, horse serum, and antimicrobial agents, was found to be as efficient as Diamond’s medium in recovering T. vaginalis from clinical specimens and may be used as a readily available, low-cost substitute for the standard medium.The combi-nation of wet-mount examicombi-nation and culture remains the standard approach for detecting T. vaginalis in patient samples.

Commercially available kits for the immunodection of T. vaginalis antigens in clinical specimens include the following types of tests: enzyme immunoassay (EIA), direct fluorescent antibody (DFA), latex agglutination (LA), and DNA probe.

Treatment. Metronidazole (Flagyl) is generally effective in vaginal trichomoniasis. As the infection can be transmitted by sexual intercourse, treatment of the sexual partner should be considered. Resistance to the drug has been reported from a number of areas but usually responds to higher doses of the drug (Lossick et al., 1986). Metronidazole also might be effective in cases of nonspecific urethritis in which T. vaginalis can be demonstrated.

Metronidazole should not be used in the first trimester of pregnancy; during the second and third trimesters or for nursing mothers it should be employed only when local palliative measures fail. Infants beyond the fourth week of life with symptomatic trichomoniasis can be treated with metronidazole 10 to 30 mg/kg daily for 5 to 8 days.