SureSwab^® Trichomonas vaginalis RNA, Qualitative TMA

T vaginalisis a single celled, pathogenic, protozoan parasite with only a trophozoite phase and no cyst stage. This organism is pear shaped with a characteristic undulating membrane and is highly motile. Since there is no cyst stage, T vaginalis does not survive long outside the host.

This organism is considered one of the most common curable, sexually transmitted infections (STI) in the United States. Some studies suggest that T vaginalis is more prevalent than Chlamydia trachomatis. Over seven million cases of T vaginalis are estimated to occur annually in both males and females. The actual number of cases may be underestimated since 1) infection with T vaginalis is not a reportable disease in the U.S.; 2) a significant number of cases are asymptomatic (10 to 50%); and 3) most tests (excluding transcription mediated amplification [TMA]) are not sensitive enough to detect the presence of this parasite.

Trichomonad infections are harbored in the urogenital tract in females and may result in vaginitis, cervicitis, and urethritis. A significant number of infected females will have copious urogenital discharge along with small hemorrhagic lesions. Complications in pregnant women include premature labor, low-birth-weight offspring, premature rupture of membranes, and post-abortion or post-hysterectomy infections. Asymptomatic infections can also occur in females.

Infections in men are predominately asymptomatic. These asymptomatic male carriers serve as a reservoir for transmission to women during sexual intercourse. The most common symptom of a trichomonad infection in men is dysuria and discharge. Infection with this organism may result in chronic prostatitis and may contribute to infertility. Trichomonad infections have also been implicated as being a cofactor for HIV transmission.

Trichomonad infections such as neonatal pneumonia are known complications. This organism may infect the newborn via contaminated secretions during the birthing process.

The T vaginalis TMA assay (manufactured by Hologic^®) is an alternative to other T vaginalis tests such as culture, wet-mount, or direct probe testing (Affirm™ Bacterial Vaginosis/Vaginitis Panel). The T vaginalis test is FDA cleared and combines the technologies of target capture, TMA, and hybridization.

After the specimen is collected for TMA testing, it is placed into a special transport solution that releases the trichomonad target rRNA and protects it from degradation. During the initial phase of testing, the target rRNA is separated by washing from the remainder of the sample.  This is performed by capturing the target rRNA through the use of a specific oligomer and magnetic microparticles.           

After the wash cycle has been completed, the target rRNA is ready for amplification. The target amplification assay is based upon the ability of complementary oligonucleotide primers to specifically anneal and allow enzymatic amplification of the target nucleic acid strands. The TMA process amplifies a specific portion of the target 16S rRNA from T vaginalis through various DNA and RNA intermediates; ultimately RNA amplicon molecules are generated.

The detection of the final RNA amplicon product is achieved through the use of nucleic acid hybridization. A labeled chemiluminescent DNA probe, complementary to a region on the amplicon product, binds the RNA to form stable RNA: DNA hybrids. A selection reagent is able to differentiate hybridized from unhybridized probes, based on chemiluminescence.

The T vaginalis TMA test is the most sensitive and specific assay available for detecting T vaginalis in clinical samples. The sensitivity of this assay approaches 100% when using vaginal and endocervical swabs and is slightly less sensitive (90% to 95%) when using urine samples. Since TMA detects rRNA targets (up to one million targets per T vaginalis trophozoite), this assay can easily detect down to one organism per sample. Specificity of the T vaginalis TMA assay approaches 100%.  

Other T vaginalis assays are less sensitive. One of the most common assays used in clinical practice to detect trichomonads is the microscopic examination of a wet mount. The test is inexpensive, but does require an experienced microscopist to detect the presence or absence of the motile trophozoites. Though highly specific, the test is much less sensitive (50% to 60%) as compared to TMA. Trichomonad culture is more sensitive (up to 75%) than direct microscopy, but requires several days for the organisms to grow before being detected by microscopic exam of the specific trichomonad culture broth. The direct probe for T vaginalis (Affirm™) was shown to be statistically less sensitive (63%) than TMA for detecting this organism. Papanicolaousmears are considered to have a sensitivity of less than 10% for trichomonads (see references 1 and 2).

The drugs of choice for treating trichomonad infections are either metronidazole or tinidazole. All sexual partners of infected patients should be treated. Treatment failures are most commonly due to lack of compliance in taking the drugs. True metronidazole resistance has been described and may be increasing.  Patients should always discuss specific treatment options with their doctors.