The microscopic image of a vaginal wet mount, stained with Giemsa, reveals the organism shown above. Which of the following is the most likely identification?

Explanation

## Image Findings * A **pear-shaped to ovoid organism** is visible. * A **single, prominent flagellum** (or a tuft of flagella, with one clearly visible) extends from the anterior end. * A **darkly stained nucleus** is present within the cytoplasm. * The organism appears stained purple with what resembles a Giemsa-like stain. * The size is approximately **10-20 µm**, larger than typical bacteria or yeast. ## Diagnosis **Key Point:** The image displays a **Trichomonas vaginalis trophozoite**, characterized by its pear shape, flagella, and nucleus. **Trichomonas vaginalis** is a flagellated protozoan that causes trichomoniasis, a common sexually transmitted infection (STI). The organism exists only in the trophozoite stage; there is no cyst stage. It is typically identified microscopically in a wet mount of vaginal secretions, where its characteristic **jerky motility** (though not visible in a static image) and morphology are diagnostic. The organism is pear-shaped, measures about 10-20 µm, and possesses 4 anterior flagella and a fifth flagellum incorporated into an undulating membrane. A prominent nucleus is also visible. ## Differential Diagnosis | Feature | Trichomonas vaginalis trophozoite | Candida albicans yeast | Gardnerella vaginalis (clue cell) | | :---------------- | :--------------------------------- | :--------------------- | :--------------------------------- | | **Morphology** | Pear-shaped, flagellated | Oval budding yeast, pseudohyphae | Epithelial cell covered with coccobacilli | | **Motility** | Jerky, tumbling (on wet mount) | Non-motile | Non-motile (bacteria are motile but not the clue cell itself) | | **Size** | 10-20 µm | 4-6 µm (yeast) | Epithelial cell (large), bacteria (small) | | **Key Features** | Flagella, undulating membrane | Budding, pseudohyphae | Stippled appearance of epithelial cell | | **pH of discharge** | >4.5 | <4.5 | >4.5 | ## Clinical Relevance **Clinical Pearl:** Trichomoniasis often presents with **frothy, greenish-yellow vaginal discharge**, pruritus, dysuria, and dyspareunia. Men are often asymptomatic carriers. ## High-Yield for NEET PG **High-Yield:** The absence of a cyst stage is a crucial distinguishing feature of *Trichomonas vaginalis* compared to other intestinal protozoa like *Entamoeba histolytica* or *Giardia lamblia*. **Key Point:** The characteristic "jerky" or "tumbling" motility is pathognomonic on a fresh wet mount. ## Common Traps **Warning:** Confusing *Trichomonas* with white blood cells on a wet mount is a common error, especially if motility is not observed or if the organism is degenerated. Look for flagella and the distinct pear shape. ## Reference [cite:Jawetz, Melnick, & Adelberg's Medical Microbiology, 28th Edition, Chapter 46]