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Trichomonas vaginalis (TV) is the most common curable sexually transmitted infection worldwide. Annually, 7.4 million new infections are estimated in the United States, which is greater than combined new cases of Chlamydia, gonorrhea, and syphilis. Serious adverse reproductive health outcomes including pregnancy complications, pelvic inflammatory disease, and an increased risk of HIV acquisition have been linked to TV infection. There are several sensitive and specific diagnostic tests available, including a newly approved nucleic acid amplification test (NAAT) that utilizes the same instrumentation platform and clinical sample as Chlamydia and gonorrhea tests. In this article, we review TV pathogenicity, adverse reproductive health outcomes, detection, and treatment followed by clinical scenarios for which TV diagnosis may prove useful in obstetrics and gynecology practice.
Obstetricians and gynecologists, family physicians
After completing this CME activity, physicians should be better able to incorporate TV counseling and testing into standard clinical practice, compare and contrast available TV diagnostic tests, and manage TV in pregnant and nonpregnant women.
Incident Trichomonas vaginalis (TV) infections in the United States are estimated at 7.4 million annual cases, which totals more than gonorrhea, Chlamydia, and syphilis infections combined.1,2 It is emerging as a serious reproductive tract pathogen, mainly affecting minorities and people living in poor or disadvantaged communities. Although TV is listed as one of Centers for Disease Control and Prevention's (CDC's) top 5 neglected parasitic infections in the United States, TV continues to be excluded from public health sexually transmitted disease (STD) control programs and is not a reportable infection.3
In an article presented to the Southern Surgical Association in 1941, Brady and Reid4 stated, “The importance of these recurring exacerbations of Trichomonas vaginalis vaginitis cannot be overemphasized, for in women during menstrual life the Trichomonas vaginalis is probably the commonest cause of leucorrhea.” Such early reports in the literature highlight the pervasive and recurrent nature of TV. Indirectly, they also reflect popular thought that TV is a harmless, nuisance parasite. Yet, in recent years, serious adverse health outcomes including pregnancy complications, pelvic inflammatory disease, and an increased risk of acquiring HIV have been linked to TV infection.5–9
Trichomonas vaginalis was first discovered in 1836 by European physician Alfred Donné.10 It is a single, spherical, motile, flagellated parasite with a barbed tail (called an axostyle) that resides in the urogenital tract of humans Trichomonads are anaerobic, reproduce via binary fission, and require carbohydrates (ie, vaginal glycogen) as an energy source.11 Symptoms and signs of TV infection may be attributed to TV attachment to vaginal epithelial cells through its barbed tail, expression of a highly immunogenic surface protein (P270), and secretion of cysteine proteinases and a cell-detaching factor.12,13 These events may lead to an intense host inflammatory response, genital tract symptoms, tissue damage, and various reproductive sequelae.
The TV genome sequence was reported in 2007, and a 2-type population structure has since emerged in a global sample of women.14 In a study by Conrad et al,15 participants diagnosed with TV were infected with either type 1 or type 2 in near-equal frequencies, whereas 10% of women harbored both types. Type 1 isolates were easier to detect by wet mount and may represent symptomatic patients with high parasite loads. Furthermore, this study did not find a statistically significant difference in vaginal pH or positive “whiff” test in women infected with the different types. However, type 2 isolates demonstrated a significantly higher minimum lethal concentration of metronidazole necessary to kill isolates compared with type 1, which may be responsible for metronidazole resistance.15 Last, a double-stranded RNA virus, referred to as TV virus, was detected in 73% of type 1 isolates and 2.5% of type 2 isolates. Trichomonas vaginalis viruses have been shown to alter the surface expression of P270 and cysteine proteinases, which conceivably can modulate TV pathogenicity.12,16
Trichomonas vaginalis infection or the host inflammatory response to infection may reduce chorioamnionic membrane strength and predispose infected women to premature rupture of membranes and preterm birth (PTB).17,18 In vitro, TV significantly impaired the biomechanical strength of human fetal membranes by reducing bursting tension, work to rupture, and elasticity in an inoculum-dependent manner.19 Both viable trichomonads and soluble factors present in parasite-free culture media damaged membranes. Although TV's direct and indirect factors are likely involved in the pathogenesis of premature rupture of membranes, the precise mechanism remains unknown.20
The National Institutes of Health funded a multicenter longitudinal study in the early 1980s, which included more than 13,000 racially and ethnically diverse pregnant women, to explore the association between TV and adverse pregnancy outcomes.21 Culture-proven TV prevalence was 12.6% overall, and 22.8% in blacks, 6.6% in Hispanics, and 6.1% in whites. After adjusting for confounders, TV was independently associated with a 30% increase in low-birth-weight (LBW) infants and a 30% increase in PTB. Furthermore, the authors attributed 3.6% of all LBW infants to maternal TV infection; in blacks, the attributable risk was 11%; in Hispanics, 1.6%; and in whites, 1.5%.5 Collectively, the medical community began to consider TV as more than a harmless inhabitant of the human vagina.
Subsequently, a large multicenter randomized placebo-controlled trial was conducted in the late 1990s to determine if treatment of asymptomatic TV reduced the incidence of PTB (<37 0/7 weeks) and LBW infants (<2500 g).22Trichomonas vaginalis was diagnosed by culture, and asymptomatic women were randomized to metronidazole therapy or placebo between 16 0/7 and 23 6/7 weeks of gestation. The risk of PTB was greatest among the asymptomatic women who were treated with metronidazole compared with women in the placebo group (risk ratio [RR], 1.8; 95% confidence interval [CI], 1.2–2.7). There was no difference between groups in the risk of delivering an LBW infant (RR, 1.4; 95% CI, 0.9–2.1) or delivering less than 35 weeks (RR, 1.3; 95% CI, 0.7–2.3).22 The authors concluded that use of metronidazole to treat asymptomatic TV during pregnancy not only does not prevent preterm delivery, but also might actually increase its risk. However, the trial had several limitations, some of which the authors acknowledged. It is unlikely metronidazole triggered PTB because it was last administered before 30 weeks, whereas the greatest increase in PTB was at 35 to 36 weeks. The authors were unable to provide a plausible, evidence-based explanation for this delay. Furthermore, the dosing regimen used in this study is not used clinically to treat TV today. The standard is 2 g as a single dose, but this study used 2 g followed at 48 hours by another 2 g between 8 and 22 6/7 weeks, plus a second identical course at 24 to 29 6/7 weeks. To reach the total of 8 g used in this study, a patient would need to be treated 4 times. Although the researchers did a tremendous effort in conducting the multicenter trial, definitive conclusions regarding causation or association between metronidazole treatment of asymptomatic TV and PTB cannot be generated. Further research is required to confirm or refute the association and to prove causality.
Few data suggest that newborns may become infected with TV during birth. Trussell et al23–25 reported the first case of newborn TV infection in 1942. Since then, there have been an additional half-dozen reports in the literature.23–25 Transmission is proposed to occur through direct vulvovaginal contamination during birth or through ingestion of maternal secretions. If ingested, the parasite may travel through the gastrointestinal tract, deposit in stool, and subsequently contaminate the vagina. Symptoms and signs of newborn TV infection range from irritability, cloudy-white vaginal discharge, fever, urinary tract infection, and respiratory distress. The prevalence of newborn infection, however, is unknown, and hence the burden of morbidity cannot be determined accurately.
Trichomonas vaginalis has emerged as a cofactor for HIV transmission. Potential mechanisms for increased susceptibility include (1) recruitment of HIV target cells (ie, CD4+ T cells) to the genital tract as a result of the host immune response to TV, (2) degradation of HIV-protective factors such as secretory leukocyte protease inhibitor, and (3) direct and indirect cytotoxic effects of the parasite itself.13,26,27Trichomonas vaginalis secretes a cell-detaching factor that releases epithelial cells from tissue, thereby weakening the structural integrity and defense barrier against HIV invasion.28Trichomonas vaginalis also elicits punctuate microhemorrhages in mucosal genital tract tissue, which may serve as a portal for HIV entry.
Investigators report an increased risk of HIV acquisition among female sex workers diagnosed with TV in Zaire (RR, 1.7; 95% CI, 1.1–2.8) and Kenya (RR, 1.5; 95% CI, 1.04–2.24).8,29 In a lower-risk general African population, the odds of acquiring HIV were 2-fold higher in women who tested positive for TV by polymerase chain reaction (PCR) compared with women who tested negative for infection (adjusted odds ratio, 2.74; 95% CI, 1.25–6.00).9 Furthermore, among HIV serodiscordant couples, women with TV at baseline were at greater risk for HIV acquisition (RR, 2.57; 95% CI, 1.42–4.65).6 Taken together, these data suggest that TV infection may increase susceptibility to HIV acquisition among women, especially in the black population who are at highest risk for both TV and HIV.
Last, TV has been associated with up to 30% of acute salpingitis cases and 16% of postpartum endometritis cases.30,31 Trichomonads have been cultured from the fallopian tubes, peritoneal fluid, and pouch of Douglas during laparoscopy. Recently, Reighard et al32 demonstrated an increase in endometrial leukocyte subpopulations in women with culture-proven TV. Trichomonas vaginalis phagocytoses bacteria, yeast, vaginal epithelial cells, mycoplasmas, and herpesviruses in vitro.33–35 These experiments have led some investigators to speculate that motile trichomonads may be capable of carrying other infectious microorganisms from the lower genital tract to the upper genital tract.7 Although there is evidence linking TV infection to upper genital tract infection, no conclusive evidence of causality exists.36
Trichomonas vaginalis is transmitted through sexual contact (heterosexual or same-sex partners) or vertically through vaginal delivery.37,38 The incubation period is between 4 and 28 days.39 Men may present with symptoms of nongonococcal urethritis (ie, urethral discharge, irritation, or dysuria), whereas the most common symptom in women is a malodorous vaginal discharge. Women may also report dyspareunia, dysuria, lower abdominal pain, or vulvovaginal irritation.40,41 However, more than 50% of women and more than 75% of men infected with TV are asymptomatic.1,37
Trichomonas vaginalis has been isolated from the vagina, cervix, urethra, periurethral glands, Bartholin glands, bladder, fallopian tubes, pouch of Douglas, prostate, and kidney.1,42 Common signs in women include vulvovaginal erythema, edema, frothy yellow-gray or green vaginal discharge, elevated pH (>6), and rarely a “strawberry” cervix.
Trichomonas vaginalis does not survive long in acidic environments. In vitro, TV rapidly dies and lyses at pH less than 5.0.19 Vaginal secretions in women infected with TV often have a pH greater than 4.5, and application of 10% potassium hydroxide solution may release amines, and a sharp fishy odor is detected (commonly called the “whiff” test).
Culture is the criterion standard for diagnosis of TV, although this method requires incubation of vaginal secretions for 3 to 5 days and daily microscopic examinations. It has not been routinely adopted into clinical settings because of time constraints, but it is often used in research. Immediate microscopic evaluation of vaginal secretions, a “wet-prep,” from symptomatic patients is simple, rapid, and inexpensive. A wet-prep may reveal oval or round, flagellated trichomonads and many polymorphonuclear cells. Because trichomonads can be similar in size and shape to white blood cells, jerky or spinning motions are necessary to make a diagnosis. Variables that can result in a false-negative test include low parasite load, time interval between specimen collection and microscopic examination (>10 minutes), and clinician skill.43 As a result, almost half of the TV cases may be missed (Table 1). Of note, wet mount and culture perform best in symptomatic patients.44
There are 2 Food and Drug Administration (FDA)–approved point-of-care tests commercially available in the United States. Both have greater sensitivity compared with wet-prep in symptomatic patients. OSOM (Sekisui Diagnostics, Tokyo, Japan) TV is an inexpensive immunochromatographic dipstick test with high sensitivity and specificity. Results are available within 10 minutes. Affirm VPIII (Becton Dickinson, Franklin Lakes, NJ) is a DNA hybridization probe test, and results are available within an hour. In areas of high rates of loss to follow-up or in an emergency room setting, rapid testing may be useful.
Nucleic acid amplification tests, such as PCR or transcription-mediated amplification (TMA), are generally more sensitive than nonamplified tests. The same endocervical swab that is used for detection of gonorrhea and Chlamydia can be used to detect TV using a recently FDA-approved TMA assay (APTIMA, GenProbe, San Diego, CA). Schwebke et al45 conducted a large, national multicenter FDA trial among 1025 women attending obstetrics/gynecology, family planning, or STD clinics to validate the NAAT performance characteristics in urine, endocervical and vaginal swabs, and ThinPrep samples. With an overall TV prevalence of nearly 12.7%, they reported superior performance of the TV NAAT (Table 1). This TMA assay has been compared with an earlier widely used research PCR assay and was found to be extremely sensitive and specific.46 In addition to the stand-alone APTIMA TMA, LabCorp offers the same TMA assay (NuSwab) as part of its vaginitis test panel and Becton Dickinson recently completed a clinical trial utilizing strand displacement amplification technology (BD ProbeTec).
Medicated tampons, mercurochrome, powdered boric acid, and bisodol, alkaline, and permanganate douches were prescribed for symptomatic relief in women without cure before the introduction of metronidazole in 1959. Metronidazole and tinidazole, which are select agents of the 5-nitroimidazole group, can cure TV. Systemic therapy is preferred over topical applications to achieve adequate drug concentrations in nonvaginal sites such as the urethra and periurethral glands. Cure rate for single 2-g dose oral metronidazole is 90% to 95%, whereas tinidazole cure rate approaches 100%.1 Tinidazole's greater cure is related to its longer half-life, higher tissue concentrations, and lower minimum lethal concentration.48 Metronidazole-resistant TV is estimated to occur in 2.5% to 5% of cases but is considered relative. Increasing the dose of metronidazole or switching to tinidazole can usually overcome the resistance.49,50 To prevent reinfection, sexual partners of infected patients should be treated. The Centers for Disease Control and Prevention recommends either regimen as first-line in male and female patients, but advises caution during pregnancy (Table 2).1
Historically, metronidazole therapy during pregnancy had been controversial. There was concern regarding teratogenicity because metronidazole readily crosses the placenta. Indeed, there are a few case reports of midline facial defects in infants born to mothers exposed to metronidazole during 6 to 7 weeks of pregnancy; however, most retrospective cohort studies do not find an association.51,52 Moreover, a meta-analysis that evaluated 32 studies, 7 of which included first-trimester exposure, did not find metro-nidazole to be teratogenic.53 In summary, the body of evidence suggests that metronidazole therapy during pregnancy, including the first trimester, does not lead to congenital malformations.
To reduce neonatal exposure, breast-feeding may be interrupted during metronidazole treatment and for 12 to 24 hours after the last dose. In mothers using tinidazole, it is recommended to interrupt breast-feeding for 3 days after the last dose.1
Overall, there remain several gaps in the literature regarding TV prevention, infection, and pathogenicity. Presumably, prevention efforts are lacking because there are insufficient data regarding reproductive harm or cost-effectiveness of screening and treatment of TV. In time, recent advancements in TV diagnostics will allow further progress of the field. However, until National STD guidelines advocate for TV screening, we present a few clinical scenarios pertinent to obstetric and gynecologic practice in which the diagnosis of TV may prove useful.
In summary, TV has emerged as a serious reproductive tract pathogen, mainly affecting minorities and people living in poor or disadvantaged communities. Incident cases in the United States are estimated to total more than gonorrhea, Chlamydia, and syphilis cases combined.1,2 A recent prevalence study reported TV infection in 20.2% of black women with and without symptoms.55 Despite these staggering statistics, trichomoniasis is not a reportable infection, nor is it a component of STI surveillance and control programs.
Trichomonas vaginalis is one of CDC's neglected parasitic infections, which are a group of 5 parasitic diseases that have been targeted as priorities for public health action. With the introduction of newer diagnostic testing, more attention can be devoted to surveillance, prevention, and/or treatment. Because of the increasing burden of TV in certain obstetric populations, the question of whether TV screening and treatment during pregnancy improve perinatal outcomes should be readdressed. In addition, the association with pelvic inflammatory disease and HIV acquisition is troubling. No longer can we afford to continue to disregard this destructive parasite by not screening at-risk patients.
Dr Gaydos has disclosed that her institution was a recipient of grant/research funding from Gen-Probe and that she received a consulting fee or honorarium and support for travel to meetings from Gen-Probe and his spouse/life partner (if any) have no financial relationships with, or financial interests in, any commercial organizations pertaining to this educational activity. All remaining authors and staff in a position to control the content of this CME activity and their spouses/life partners (if any) have disclosed that they have no financial relationships with, or financial interests in, any commercial organizations pertaining to this educational activity. However, Lippincott CME Institute has identified and resolved all conflicts of interest concerning this educational activity.