Protozoan Infections of the Urogenital System
By the end of this section, you will be able to:
- Identify the most common protozoan pathogen that causes infections of the reproductive system
- Summarize the important characteristics of trichomoniasis
Only one major protozoan species causes infections in the urogenital system. Trichomoniasis, or “trich,” is the most common nonviral STI and is caused by a flagellated protozoan Trichomonas vaginalis. T. vaginalis has an undulating membrane and, generally, an amoeboid shape when attached to cells in the vagina. In culture, it has an oval shape.
It is found only as a trophozoite and does not form cysts. T. vaginalis can adhere to cells using adhesins such as lipoglycans; it also has other cell-surface virulence factors, including tetraspanins that are involved in cell adhesion, motility, and tissue invasion. In addition, T. vaginalis is capable of phagocytosing other microbes of the normal microbiota, contributing to the development of an imbalance that is favorable to infection.
Anyone can develop trichomoniasis. Males are generally asymptomatic, and although females are more likely to develop symptoms, they are often asymptomatic as well. When symptoms do occur, they are characteristic of urethritis. Males experience itching, irritation, discharge from the penis, and burning after urination or ejaculation. Females experience dysuria; itching, burning, redness, and soreness of the genitalia; and vaginal discharge. The infection may also spread to the cervix. Infection increases the risk of transmitting or acquiring HIV and is associated with pregnancy complications such as preterm birth.
Microscopic evaluation of wet mounts is an inexpensive and convenient method of diagnosis, but the sensitivity of this method is low (see the micrograph below). Nucleic acid amplification testing (NAAT) is preferred due to its high sensitivity. Using wet mounts and then NAAT for those who initially test negative is one option to improve sensitivity. Samples may be obtained for NAAT using urine, vaginal, or endocervical specimens for females and with urine and urethral swabs for males. It is also possible to use other methods such as the OSOM Trichomonas Rapid Test (an immunochromatographic test that detects antigen) and a DNA probe test for multiple species associated with vaginitis (the Affirm VPIII Microbial Identification Test discussed in Fungal Infections of the Reproductive System). (Association of Public Health Laboratories, “Advances in Laboratory Detection of Trichomonas vaginalis,” 2013.) T. vaginalis is sometimes detected on a Pap test, but this is not considered diagnostic due to high rates of false positives and negatives. The recommended treatment for trichomoniasis is oral metronidazole or tinidazole. Sexual partners should be treated as well.
Check Your Understanding
What are the symptoms of trichomoniasis?
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Eye on Ethics. STIs and Privacy
For many STIs, it is common to contact and treat sexual partners of the patient. This is especially important when a new illness has appeared, as when HIV became more prevalent in the 1980s. But to contact sexual partners, it is necessary to obtain their personal information from the patient. This raises difficult questions. In some cases, providing the information may be embarrassing or difficult for the patient, even though withholding such information could put their sexual partner(s) at risk.
Legal considerations further complicate such situations. The Health Insurance Portability and Accountability Act (HIPAA), passed into law in 1996, sets the standards for the protection of patient information. It requires businesses that use health information, such as insurance companies and healthcare providers, to maintain strict confidentiality of patient records. Contacting a patient’s sexual partners may therefore violate the patient’s privacy rights if the patient’s diagnosis is revealed as a result.
From an ethical standpoint, which is more important: the patient’s privacy rights or the sexual partner’s right to know that they may be at risk of a sexually transmitted disease? Does the answer depend on the severity of the disease or are the rules universal? Suppose the physician knows the identity of the sexual partner but the patient does not want that individual to be contacted. Would it be a violation of HIPAA rules to contact the individual without the patient’s consent?
Questions related to patient privacy become even more complicated when dealing with patients who are minors. Adolescents may be reluctant to discuss their sexual behavior or health with a health professional, especially if they believe that healthcare professionals will tell their parents. This leaves many teens at risk of having an untreated infection or of lacking the information to protect themselves and their partners. On the other hand, parents may feel that they have a right to know what is going on with their child. How should physicians handle this? Should parents always be told even if the adolescent wants confidentiality? Does this affect how the physician should handle notifying a sexual partner?
Clinical Focus. Resolution
Vaginal candidiasis is generally treated using topical antifungal medications such as butoconazole, miconazole, clotrimazole, tioconazole, nystatin, or oral fluconazole. However, it is important to be careful in selecting a treatment for use during pregnancy. Nadia’s doctor recommended treatment with topical clotrimazole. This drug is classified as a category B drug by the FDA for use in pregnancy, and there appears to be no evidence of harm, at least in the second or third trimesters of pregnancy. Based on Nadia’s particular situation, her doctor thought that it was suitable for very short-term use even though she was still in the first trimester. After a seven-day course of treatment, Nadia’s yeast infection cleared. She continued with a normal pregnancy and delivered a healthy baby eight months later.
Higher levels of hormones during pregnancy can shift the typical microbiota composition and balance in the vagina, leading to high rates of infections such as candidiasis or vaginosis. Topical treatment has an 80–90% success rate, with only a small number of cases resulting in recurrent or persistent infections. Longer term or intermittent treatment is usually effective in these cases.
The case began in Anatomy and Normal Microbiota of the Urogenital Tract.
Disease Profile. Fungal and Protozoan Reproductive Tract Infections
The table below summarizes the most important features of candidiasis and trichomoniasis.
| Disease | Pathogen | Signs and Symptoms | Transmission | Diagnostic Tests | Antimicrobial Drugs |
|---|---|---|---|---|---|
| Trichomoniasis | Trichomonas vaginalis | Urethritis, vaginal or penile discharge; redness or soreness of female genitalia | Sexual contact | Wet mounts, NAAT of urine or vaginal samples; OSOM Trichomonas Rapid Test, Affirm VPIII Microbial Identification Test | Metronidazole, tinidazole |
| Vaginal candidiasis (yeast infection) | Candida spp., especially C. albicans | Dysuria; vaginal burning, itching, discharge | Transmissible by sexual contact, but typically only causes opportunistic infections after immunosuppression or disruption of vaginal microbiota | Culture, Affirm VPIII Microbial Identification Test | Fluconazole, miconazole, clotrimazole, tioconazole, nystatin |
Link to Learning
Take an online quiz for a review of sexually transmitted infections (the University of Arizona Biology Project’s sexually transmitted diseases problem set, at biology.arizona.edu).
Summary
- Trichomoniasis is a common STI caused by Trichomonas vaginalis.
- T. vaginalis is common at low levels in the normal microbiota.
- Trichomoniasis is often asymptomatic. When symptoms develop, trichomoniasis causes urinary discomfort, irritation, itching, burning, discharge from the penis, and vaginal discharge.
- Trichomoniasis is treated with the antiflagellate drugs tinidazole and metronidazole.
Key terms
- Trichomoniasis — a common STI caused by Trichomonas vaginalis.
Practice
Identify the most common protozoan pathogen that causes infections of the reproductive system
Trichomoniasis is caused by ________.
Name the flagellated protozoan this section discusses throughout, printed in italics.What is the only common infection of the reproductive tract caused by a protozoan?
This section names only one protozoan disease of the reproductive tract; the other three options are caused by bacteria or fungi covered in neighboring sections.Name three organisms (a bacterium, a fungus, and a protozoan) that are associated with vaginitis.
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Summarize the important characteristics of trichomoniasis
Which test is preferred for detecting T. vaginalis because of its high sensitivity?
Compare this section’s description of wet-mount sensitivity with the method it recommends when a wet mount tests negative.What informal nickname does this section use for trichomoniasis?
It appears in quotation marks in the section’s opening sentence.In culture, Trichomonas vaginalis has a(n) ________ shape.
Contrast this with its amoeboid shape when attached to vaginal cells.Trichomoniasis is treated with the antiflagellate drugs tinidazole and ________.
This section’s Summary names two antiflagellate drugs; the other is tinidazole.Why is nucleic acid amplification testing (NAAT) preferred over wet mount microscopy for diagnosing trichomoniasis?
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This section is adapted from Microbiology, Section 23.6: Protozoan Infections of the Urogenital System by Nina Parker, Mark Schneegurt, Anh-Hue Thi Tu, Philip Lister, Brian M. Forster, and OpenStax, © OpenStax, licensed under CC BY-NC-SA 4.0. Access the original for free at openstax.org. Changes: the Link to Learning’s redirect (openstax.org/l/22quizstireview, to www.biology.arizona.edu/human_bio/problem_sets/stds/stds.html) returned 404 on September 14, 2026, so the callout names the resource and its site in plain text instead of linking it; the module’s one figure is re-encoded as WebP and rendered as a mediafigure, kind="photo", eager="true" as the page’s first figure, its alt rewritten from the image (the source alt’s “larger oval cells,” plural, is imprecise — the artwork shows one larger labeled oval cell plus a separate cluster of smaller round cells) rather than copied from the source alt; the module’s one footnote (Association of Public Health Laboratories, 2013) is rendered as an inline parenthetical citation after the sentence it supports, its bare access URL dropped; the plain-text cross-reference to “section 23.5” (the Affirm VPIII Microbial Identification Test) is rendered as a link to Fungal Infections of the Reproductive System, which lands in this same run. The Disease Profile table image (OSC_Microbio_23_06_FungInfTbl) is transcribed as a Markdown table rather than vendored, per this book’s Disease Profile rule, checked cell by cell against the PDF page: both cells that print “Affirm VPII Microbial Identification Test” are corrected to “Affirm VPIII Microbial Identification Test,” matching this same module’s own two other uses of “VPIII” (and Section 23.5’s), and the alt’s stray semicolon inside “Affirm; VPII Microbial Identification Test” — which the printed table image does not show — is dropped so the test name reads as one continuous phrase; “immunosuppresion” is corrected to “immunosuppression” in the Vaginal candidiasis row’s Transmission cell. One further one-word source typo is corrected in place with no inline note: the body’s “ticonozole” is corrected to “tioconazole,” matching this module’s own Disease Profile table and Section 23.5’s body text. The Clinical Focus “Resolution” box’s “go back to the previous Clinical Focus box” link is replaced with a plain sentence naming that the case began in Section 23.1, an absolute site-root Markdown link, since this case runs through four parts (23.1, 23.3, 23.5, this section); the Eye on Ethics box is rendered as a callout unchanged, with no item built from its embedded questions, since the source does not print them as a bulleted list. This section’s one body Check Your Understanding bullet (“What are the symptoms of trichomoniasis?”) stays a self-check, since the honest answer needs both the module’s male-symptom sentence and its separate female-symptom sentence. The module’s two Multiple Choice and one Fill in the Blank items are rendered as scored components in source order with their source keys and source option order. The module’s one Short Answer question, which prints no source key, is graded as a self-check whose model answer and rubric name a bacterium, a fungus, and a protozoan associated with vaginitis, drawing on this section’s own Trichomonas vaginalis, Section 23.3’s Gardnerella vaginalis, and Section 23.5’s Candida albicans — a synthesis across this chapter’s own sibling sections, since no single sentence of this module answers the question alone. Key terms are compiled from the module’s one class-less defined-term element, giving one glossary-sourced bullet. Four additional items (a term-recall textin, two body-sentence clozes, and a self-check paraphrasing the module’s diagnostic-method paragraph) are added to the Practice block to reach this book’s per-objective and per-section floors, since the module carries only three keyed exercises and one unkeyed one. No source exercise, table, or Check Your Understanding bullet is omitted.