The microscopic image of a stool sample shown above reveals an ovum with characteristic features. Which of the following parasites is most likely identified?

Explanation

## Image Findings * **Oval-shaped egg** with rounded ends. * **Thin, smooth, colorless shell**. * Contains a **developing embryo in the morula stage** (typically 2-8 cell stage, though more cells are visible here, indicating further development). * The embryo fills most of the egg, with a clear space between the embryo and the shell. ## Diagnosis **Key Point:** The image shows a **hookworm egg**, characterized by its oval shape, thin smooth shell, and a developing morula-stage embryo. Hookworm eggs, belonging to either *Ancylostoma duodenale* or *Necator americanus*, are typically 40-70 µm long and 20-40 µm wide. They are passed in feces at the 2- to 8-cell morula stage, which is clearly visible in the image. The thin, transparent shell is a distinguishing feature, differentiating it from other common helminth eggs. ## Differential Diagnosis | Feature | Hookworm (Ancylostoma/Necator) | Ascaris lumbricoides (Fertilized) | Trichuris trichiura (Whipworm) | Enterobius vermicularis (Pinworm) | | :---------------- | :------------------------------- | :-------------------------------- | :----------------------------- | :-------------------------------- | | **Shape** | Oval, rounded ends | Oval to round | Barrel-shaped | D-shaped (plano-convex) | | **Shell** | Thin, smooth | Thick, mammillated (bumpy) | Thick, smooth | Thin, smooth | | **Contents** | Morula (2-8 cell embryo) | Unsegmented ovum or early larva | Unsegmented ovum | Fully developed larva | | **Polar Plugs** | Absent | Absent | Present (at both ends) | Absent | ## Clinical Relevance **Clinical Pearl:** Hookworm infection (Ancylostomiasis or Necatoriasis) is a common cause of **iron deficiency anemia** in tropical and subtropical regions, especially in India. The adult worms attach to the intestinal mucosa and feed on blood, leading to chronic blood loss. ## High-Yield for NEET PG **High-Yield:** Identification of hookworm eggs in stool is the **gold standard for diagnosis** of hookworm infection. The eggs are typically found in fresh stool samples; if stool is left at room temperature, the larvae may hatch, making identification more challenging. **Key Point:** Both *Ancylostoma duodenale* and *Necator americanus* eggs are morphologically indistinguishable, and are reported simply as "hookworm eggs" in routine stool examinations. ## Common Traps **Warning:** Confusing hookworm eggs with *Ascaris* eggs (due to similar size range) is a common trap. Remember the **mammillated outer shell of *Ascaris*** and the **thin, smooth shell with morula of hookworm**. ## Reference [cite:Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, Chapter 286: Hookworm Infection]