Trichomonas

OVERVIEW: What every clinician needs to know

Parasite name and classification

Trichomonas vaginalis – flagellated protozoan; the sole host for this organism is humans.

What is the best treatment?

Metronidazole 2g orally once, OR
Tinidazole 2g orally once, OR
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Metronidazole 500mg orally twice daily for 7 days (preferred in HIV-infected women)
In most patients, the one-time dose is as effective, and compliance is improved, compared to the longer course.
In HIV-infected women there are some data to suggest that the longer course (500mg orally twice daily for 7 days) is more effective at eradicating infection.
Male partners of infected women should be treated with one of the single dose regimens above.
Refractory or recurrent disease may be treated with metronidazole or tinidazole 2g daily for 5 days.
Topical intravaginal metronidazole gel is less effective than oral treatment and should not be used.
There are issues of metronidazole resistance which can often be overcome with high dose metronidazole or tinidazole treatment-culture and susceptibility testing can be coordinated by contacting US Centers for Disease Control and Prevention.

What are the clinical manifestations of infection with this organism?

Many infections are asymptomatic in women and men.
Key symptoms in women are those of vaginitis and may include malodorous discharge, dysuria, dyspareunia and pruritus.
On pelvic exam in infected women, there may classically be copious, thin, malodorous frothy discharge and vaginal vault erythema and edema.
Punctate hemorrhages on the cervix (strawberry cervix) may also be seen.
Findings in men are usually absent, but occasionally men experience dysuria, urethral discomfort and discharge.

Do other diseases mimic its manifestations?

Other causes of vaginitis in women can mimic trichomoniasis, including Candida vaginitis and bacterial vaginosis.
Other STDs such as chlamydia infection and gonorrhea may also present in a similar fashion.
Other causes of urethritis in the differential diagnosis for men include chlamydia, gonorrhea and Mycoplasma genitalium.

What laboratory studies should you order and what should you expect to find?

Results consistent with the diagnosis:

Routine laboratory tests, including the white blood count (WBC) and differential, and comprehensive metabolic panels are usually normal.

Results that confirm the diagnosis

Vaginal wet mount microscopy performed immediately may reveal the motile, pear shaped organisms. However, wet mount has only 60% sensitivity for infection in some studies.
T. vaginalis can also be cultured in liquid media, most commonly Diamond’s medium, but this is only available in select laboratories. Commercially available culture systems are able to detect infection in 3 days. Sensitivity is 70-80% and specificity is 100%.
The most sensitive commercially available tests include point of care tests (which detects T. vaginalis antigen) or lab-based nucleic acid amplification tests (NAAT). NAAT has a sensitivity of 97-100% and a specificity of 98-100% for infection. This is the test of choice for T. vaginalis infections.

What imaging studies will be helpful in making or excluding the diagnosis?

Imaging studies are not helpful.

What complications can be associated with this parasitic infection, and are there additional treatments that can help to alleviate these complications?

Trichomoniasis has been associated with an increased risk of HIV infection, cellulitis post-hysterectomy, pelvic inflammatory disease in HIV-infected women, epididymitis and prostatitis in men, and premature rupture of membranes and low infant birth weight in pregnant women.

What is the life cycle of the parasite, and how does the life cycle explain infection in humans?

Trichomonas vaginalis lives in the female lower genital tract and the male prostate and urethra.
There are non-pathogenic trichomonads that can inhabit the oral cavity.
Trichomonas vaginalis divides by binary fission, and does not appear to have a cyst form.
The life cycle can be found on the CDC website.
Humans are the only known reservoir of infection.
Transmission is primarily sexual.
The incidence of infections in the United States is estimated to be between 3-5 million annually.
Prevalence has been estimated at 3% of the women age 13-49 in the United States.
Prevalence increases with age, and African American women have higher rates of infection than white women.
Infection control issues:

Prophylactic antibiotic treatment is not recommended

There is no vaccine available

Sex partners of patients diagnosed with trichomoniasis should be empirically treated as there are high rates of concurrent infection

Condoms reduce the risk of transmission

How does this organism cause disease?

T. vaginalis causes damage to host epithelium by direct contact with surface proteins, which result in micro-ulcerations.
Specific parasite virulence factors, as well as the host immune response, are still not fully understood but include adhesins that help with tight attachment to vaginal epithelial cells, and glycoproteins and proteinases that mediate cytotoxicity and apoptosis as well as degrade immunoglobulins and complement to evade the immune response.

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