**Entamoeba histolytica** is a protozoan parasite responsible for amoebiasis, which ranges from asymptomatic infection to severe dysentery and liver abscesses. Recognized as a significant cause of morbidity and mortality in developing countries, understanding its lifecycle, pathogenesis, clinical manifestations, diagnosis, and treatment is crucial in medical practice. ## Lifecycle and Transmission - **Transmission**: Primarily fecal-oral route, through contaminated food, water, or hands. Cysts are the infective stage, surviving outside the host in the environment. - **Lifecycle**: Ingested cysts transform into trophozoites in the small intestine. Trophozoites multiply and can invade the intestinal mucosa or reach the liver via the bloodstream, causing abscesses. Cysts and trophozoites are passed in feces, but only cysts can survive in external environments. ## Pathogenesis - **Invasion**: Trophozoites adhere to and lyse epithelial cells in the colon, causing flask-shaped ulcers. The process is facilitated by amoebic cysteine proteases, which degrade host tissues and immune factors. - **Spread**: Trophozoites can disseminate to extraintestinal sites, most commonly the liver, leading to abscess formation. Rarely, it can spread to the lungs, brain, and other organs. ## Clinical Manifestations - **Asymptomatic**: Most infections are asymptomatic, with individuals excreting cysts. - **Intestinal Amoebiasis**: Symptoms range from mild diarrhea to severe dysentery with blood and mucus in stools, abdominal pain, and fever. - **Extraintestinal Amoebiasis**: Liver abscess is the most common form, characterized by right upper quadrant pain, fever, and hepatomegaly. Abscess rupture poses a significant risk. ## Diagnosis - **Microscopy**: Detection of cysts or trophozoites in stool samples. Requires skilled personnel due to similarity with nonpathogenic amoeba. - **Serology**: Useful for diagnosing extraintestinal infection, especially liver abscesses. High sensitivity and specificity. - **Imaging**: Ultrasound or CT scans are crucial for identifying liver abscesses and other extraintestinal manifestations. - **PCR**: Offers high sensitivity and specificity for identifying E. histolytica in stool samples. ## Treatment - **Asymptomatic Carriers**: Treated with luminal agents like paromomycin or iodoquinol to eliminate cysts and prevent transmission. - **Symptomatic Intestinal Disease**: Metronidazole or tinidazole followed by a luminal agent to eradicate any remaining cysts. - **Extraintestinal Disease**: Metronidazole or tinidazole is the first-line treatment, often followed by a luminal agent. Aspiration of liver abscesses is reserved for cases not responding to medical therapy. ## Prevention - **Sanitation and Hygiene**: Improving access to clean water, proper sewage disposal, and hand hygiene are critical. - **Education**: Raising awareness about transmission and prevention methods. - **Food Safety**: Washing fruits and vegetables, boiling or filtering water, and ensuring food is cooked properly.