Trichomonas vaginalis
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p649-651
2025-10-21
103
GENERAL CHARACTERISTICS
Infection is acquired primarily through sexual inter course, hence the need to diagnose and treat asymptomatic males. The organism is capable of survival for extended periods in a moist environment such as damp towels and underclothes; however, this mode of transmission is thought to be very rare. Infection with Trichomonas vaginalis occurs worldwide. It is estimated that 5 million women and 1 million men in the United States have trichomoniasis, with an estimated 7.4 million new cases occurring annually. The prevalence of trichomoniasis worldwide is estimated to be more than 170 million cases, which does not include the number of asymptomatic cases that remain untreated. In North America, more than 8 million new cases are reported yearly, with an estimated rate of asymptomatic cases being as high as 50%. Trichomoniasis is the primary non-viral sexually transmitted disease worldwide. Infection with T. vaginalis has major health consequences for women, including complications in pregnancy, association with cervical cancer, and predisposition to HIV infection.
The life cycle of T. vaginalis has a single trophozoite stage, and is very similar in morphology to other trichomonads (Table 1). The trophozoite is 7 to 23 µm long and 5 to 15 µm wide. The axostyle is usually obvious and protrudes through the bottom of the organism, whereas the undulating membrane ends halfway down the side of the trophozoite. There are a large number of granules evident along the axostyle.
Table1. Characteristics of Trichomonas vaginalis
PATHOGENESIS AND SPECTRUM OF DISEASE
Growth of the organism results in inflammation and large numbers of trophozoites in the tissues and the secretions. As the acute infection becomes more chronic, the purulent discharge diminishes, with a decrease in the number of organisms. Symptoms such as vaginal or vulval pruritus and discharge are often sudden and occur during or after menstruation as a result of the increased vaginal acidity. Symptoms include vaginal discharge (42%), odor (50%), and edema or erythema (22% to 37%). Complaints also include dysuria and lower abdominal pain.
From 25% to 50% of infected women may be asymptomatic and have a normal vaginal pH of 3.8 to 4.2 and normal vaginal flora. Even in the carrier form, about 50% of women will become symptomatic during the following 6 months.
Although vaginitis is the most common finding in women with trichomoniasis, other complications include distention of a fallopian tube with pus, endometritis, infertility, low birth weight, and cervical erosion. There is also an increased association with HIV transmission and cervical dysplasia.
Dysuria, often the earliest symptom, occurs in about 20% of women with vaginal trichomoniasis. Infected males may be asymptomatic, or the infection may be self limited, persistent, or result in recurring urethritis. In nonspecific urethritis, T. vaginalis has been detected in 10% to 20% of subjects and in 20% to 30% of those whose sexual partners had vaginitis. Once established, the infection persists for an extended period in females but only for about 10 days or less in males. T. vaginalis is the cause of 11% of all cases of non–gonococcal urethritis in males.
Respiratory distress has been reported in a full-term, normal male infant with T. vaginalis with severe respiratory problems following delivery. A wet preparation of thick, white sputum demonstrated few leukocytes and motile flagellates, which were identified as T. vaginalis. This study supports previous data confirming that the organism may cause neonatal pneumonia.
LABORATORY DIAGNOSIS
Humans are the only natural host for T. vaginalis, and organisms reside in the vagina and prostate; they usually do not survive outside the urogenital tract. The parasites feed on the mucosal surface of the vagina, where bacteria and leukocytes are abundant. The preferred pH for good parasitic growth in females is slightly alkaline or acidic (6.0 to 6.3 optimal), not the normal pH (3.8 to 4.2) of the healthy vagina. The organisms can also be recovered in urine, in urethral discharge, or after prostatic massage. Often, the organisms are recovered in centrifuged urine sediment from both male and female patients.
Wet Mounts
The identification of T. vaginalis is often based on the examination of wet preparations of vaginal and urethral discharges, urine, and prostatic secretions. This examination must be performed within 10 to 20 minutes after sample collection; if not, organisms lose motility and may not be identified. Several specimens may need to be examined for detection of the organisms. The sensitivity associated with wet mount examinations varies between 40% and more than 80%. Often, the percent detection from this procedure is quite low with limited sensitivity and specificity.
Stained Smears
Giemsa or Papanicolaou stain can be used. However, atypical cellular changes can be misinterpreted, particularly on the Papanicolaou smear. The organisms are routinely missed on Gram stains. The number of false-positive and false-negative results reported on the basis of stained smears strongly suggests that confirmation should be accomplished by observation of motile organisms either from the direct wet mount or from appropriate culture media.
Culture
A convenient plastic envelope method has been developed, which allows immediate examination and culture in one self-contained system. This system is commercially available as the InPouchTV (BIOMED Diagnostics, San Jose, Calif), which serves as the specimen transport container, the growth chamber during incubation, and the “slide” during microscopy. Once it is inoculated, it requires no opening for examination, and positive growth will occur within 5 days. The sensitivity of this system is reported to be superior to those of other available culture methods.
Antigen Detection
Several diagnostic tests have been developed, including the XenoStrip-Tv (Xenotope Diagnostics, Inc., San Antonio, Tex) and the OSOM Trichomonas Rapid Test (Sekisui Diagnostics, Houston, TX), both of which are more sensitive than the wet mount.
Molecular Diagnostics
The use of polymerase chain reaction (PCR) methods has led to improvements in T. vaginalis detection; nonviable organisms and cells and target sequences can also be detected. In addition to various culture and transport options, there are several other products available, including the Affirm VPIII probe from Becton Dickinson (Cockeysville, Md), the Quik-Tri/Can latex agglutination from Pan Bio InDX, Inc (Baltimore, Md), and the T.VAG DFA from Chemicon (Temecula, Calif). Depending on the patient population, client base, number of requests, and cost, one or more of these options may be appropriate for a particular diagnostic laboratory.
THERAPY
Metronidazole is recommended for the treatment of urogenital trichomoniasis, although resistance to both metronidazole and other 5-nitromidazoles has been reported. It is also recommended that all sexual partners be treated simultaneously to avoid immediate reinfection. Metronidazole-resistant T. vaginalis has been implicated in an increased number of cases; unfortunately, this drug is currently the only drug approved for the treatment of trichomoniasis in the United States. Tinidazole has also been used for therapy.
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