All of the following are true regarding Entamoeba histolytica EXCEPT:

Explanation

## Entamoeba histolytica: Life Cycle & Transmission ### Correct Facts About E. histolytica **Key Point:** Cysts, NOT trophozoites, are the infective and transmissible form of E. histolytica. | Feature | Trophozoite | Cyst | |---------|-------------|------| | Motility | Motile (pseudopodia) | Non-motile | | Nuclei | 1–4 nuclei with central karyosome | 1–4 nuclei (mature cyst: 4) | | Location | Intestinal lumen & mucosa | Intestinal lumen only | | Survival | Dies in acidic stomach | Survives gastric acid | | Infectivity | Non-infective | **Infective form** | | Transmission | Not transmitted | Fecal–oral route | ### Why Option 4 is Wrong **High-Yield:** Trophozoites are NOT the transmissible form. They are fragile, killed by gastric acid, and do not survive passage through the stomach. Only cysts are infective because they have a rigid wall that protects them during transit through the GI tract and environmental exposure. ### Why the Other Options Are Correct **Option 1 (Nuclei):** Trophozoites contain 1–4 nuclei, each with a characteristic central karyosome surrounded by a clear halo—a key diagnostic feature on microscopy. **Option 2 (Cyst transmission):** Cysts are the infective form, transmitted person-to-person via contaminated food/water (fecal–oral route). This is the epidemiologically important stage. **Option 3 (Intestinal & extraintestinal disease):** E. histolytica causes both intestinal infection (dysentery, colitis) and extraintestinal manifestations (amoebic liver abscess, rarely brain/lung abscess). ### Clinical Pearl Patients with acute amoebic dysentery shed trophozoites in stool, but these are non-infective. Chronic carriers and asymptomatic individuals shed cysts, which are the true epidemiologic threat. This is why stool antigen detection and serology are more reliable than microscopy alone for diagnosis. **Mnemonic:** **CYST = Contagious, Yet Stable** — cysts are the transmissible, environmentally stable form.