--- An Overview Introduction - The term "ameba" originates from the Greek word amibe , meaning "change." - Amebae are structurally simple protozoans without a f
--- An Overview Introduction - The term "ameba" originates from the Greek word amibe , meaning "change." - Amebae are structurally simple protozoans without a fixed shape. - Taxonomic Classification : Phylum : Sarcomastigophora - Subphylum : Sarcodina - Superclass : Rhizopoda - Order : Amebida Structure - The cytoplasm is enclosed by a membrane and differentiated into: Ectoplasm : The outer layer. - Endoplasm : The inner layer. - Pseudopodia :Formed by thrusting out ectoplasm followed by endoplasm. - Function in locomotion and food capture (phagocytosis). Reproduction - Primarily occurs by: Fission : Splitting into two. - Budding : A smaller outgrowth develops and detaches. - Cysts :Formed under unfavorable conditions. - Serve as the infective stage for vertebrate hosts (e.g., Entamoeba histolytica ). Classification Amebae are categorized into: - Intestinal Amebae :Found in the alimentary canal. - Includes species like: Entamoeba histolytica (pathogenic) - Entamoeba dispar - Entamoeba coli - Entamoeba polecki - Entamoeba hartmanni - Entamoeba gingivalis - Endolimax nana - Iodamoeba butschlii - Note : Only Entamoeba histolytica is pathogenic. - Free-Living Amebae :Opportunistic pathogens that can cause infections. - Includes species like: Naegleria fowleri - Acanthamoeba spp. - Balamuthia mandrillaris Entamoeba histolytica History and Discovery - Discovered in 1875 by Losch in St. Petersburg, Russia, in dysenteric feces. - Key developments:1890: William Osler reported dysentery leading to liver abscess. - 1891: Councilman and Lafleur introduced the terms "amebic dysentery" and "amebic liver abscess" and studied its pathogenesis. Distribution - Worldwide prevalence, more common in tropical regions. - Found in poor sanitation areas, across all climates:From Alaska (61°N) to the Straits of Magellan (52°S). - Infection statistics:~10% of the global population infected. - ~50% prevalence in developing countries. - ~1% prevalence in affluent countries like the USA. - Clinical Impact :80–99% of infections are asymptomatic. - Invasive amebiasis:Affects 50 million people annually. - Causes 50,000 deaths yearly, especially in tropical regions (Asia, Africa, Latin America). - Third leading parasitic cause of death after malaria and schistosomiasis. Epidemiology in India India can be divided into three zones based on prevalence: - High Prevalence ( 30%) :Chandigarh, Tamil Nadu, Maharashtra. - Moderate Prevalence (10–30%) :Punjab, Rajasthan, Uttar Pradesh, Delhi, Bihar, Assam, West Bengal, Andhra Pradesh, Karnataka, Kerala. - Low Prevalence ( 10,000/µL) and elevated serum transaminases may be observed. - Complications :Rupture into adjacent structures: Diaphragm → Lung or pleural cavity. - Pericardium , peritoneum , stomach , intestine , or inferior vena cava . - Skin via abdominal wall, forming discharging sinuses. --- Pulmonary Amebiasis - Pathogenesis :Occurs due to extension of liver abscess through the diaphragm or rarely via direct hematogenous spread. - Common Features :Affects the lower part of the right lung . - Formation of hepatobronchial fistulas may result in expectoration of chocolate-brown sputum. - Other manifestations include pleuritic chest pain, dyspnea, and nonproductive cough. - Complications :Amebic empyema (accumulation of pus in the pleural cavity). Metastatic Amebiasis - Hematogenous Spread :Leads to abscesses in distant organs like the brain, spleen, kidneys, and adrenal glands. - Cerebral Amebiasis :Severe tissue destruction, often fatal. - Renal and Adrenal Lesions :Rare, associated with systemic spread. Cutaneous Amebiasis - Direct Extension :Seen around anus , colostomy sites , or through discharging sinuses from liver abscesses. - Clinical Features :Presents as extensive gangrenous skin destruction. - Often mistaken for condyloma or epithelioma. Genitourinary Amebiasis - Penile Amebiasis :Acquired through anal intercourse. - Lesions are ulcerative and destructive, resembling carcinoma. - Female Genital Lesions :Affects the vulva, vagina, or cervix via extension from the perineum. --- Laboratory Diagnosis - Diagnosis of Amebic Liver Abscess : Microscopy :Examination of aspirate from the abscess shows necrotic debris and few or no amebae. - Histopathology :Amebae seen at the periphery of the lesion. - Serology : Indirect Hemagglutination Assay (IHA) , ELISA , and latex agglutination tests are highly sensitive. - Imaging : Ultrasound : Detects hypoechoic lesions. - CT and MRI : Useful for detailed lesion assessment. - X-ray : Shows elevated diaphragm or pleural effusion in complicated cases. - Diagnosis of Intestinal Amebiasis : Stool Examination : Macroscopic : Foul-smelling, semi-liquid stool with blood and mucus. - Microscopy : Fresh wet mount for motile trophozoites containing RBCs. - Iodine-stained preparation for cysts. - Trichrome stain highlights nuclear and cytoplasmic details. - Charcot-Leyden crystals may be observed. - Stool Culture :Specialized media like Boeck and Drbohlav’s or Robinson’s media . - Molecular Methods :DNA probes and PCR to detect E. histolytica specifically. Summary of Clinical Features - Hepatic :Painful hepatomegaly, fever, anorexia, jaundice in severe cases. - Pulmonary :Chest pain, dyspnea, chocolate-colored sputum. - Cutaneous :Gangrenous lesions around discharging sinuses. - Genitourinary :Ulcerative lesions resembling carcinoma. Management - Pharmacologic Therapy : Metronidazole is the drug of choice for both intestinal and extraintestinal amebiasis. - Tinidazole and chloroquine are alternatives in resistant cases. - Surgical Management :Indicated for large abscesses threatening to rupture or causing compressive symptoms. - Drainage procedures include percutaneous aspiration. --- Complications - Hepatic Abscess Rupture :Into peritoneum, pleura, or pericardium. - Pulmonary Complications :Empyema, bronchopleural fistula. - Cerebral Amebiasis :Rapidly fatal if untreated. - Skin and Genitourinary Lesions :Can lead to extensive tissue destruction. Extraintestinal Amebiasis 1. Introduction Extraintestinal amebiasis is a condition where Entamoeba histolytica extends beyond the intestinal tract, leading to systemic complications. These are summarized in Flow Chart 2 and Figure 4 . 2. Sites of Involvement in Extraintestinal Amebiasis The spread occurs through portal circulation , resulting in lesions in multiple organs: - Liver : Most common site. - Lungs : Extension through the diaphragm. - Peritoneum : Secondary to rupture of liver abscess. - Skin, perianal regions, and genitals : Through direct extension or sinus drainage. - Other distant organs : Brain, kidney, spleen, and adrenal glands via hematogenous or lymphatic spread. 3. Hepatic Amebiasis A. Acute Hepatic Involvement (Amebic Hepatitis) - Caused by repeated invasion of amebae or release of toxins from the colon. - Symptoms:Enlarged, tender liver. - Absence of fever in most cases. - Liver damage attributed to lysosomal enzymes and cytokines, not directly to E. histolytica . B. Amebic Liver Abscess - Occurs in 5–10% of intestinal amebiasis cases. - Features: Content : Central necrotic tissue resembling "anchovy sauce pus" (sterile, without amebae). - Location : Right lobe of the liver (more common). - Symptoms :Painful hepatomegaly. - Fever, anorexia, nausea, weight loss, fatigue. - Leukocytosis ( 10,000/μL) and elevated transaminases in most cases. - Jaundice in severe cases with biliary tract involvement. - Complications :Rupture into the peritoneum, pleural cavity, pericardium, or externally. - Rupture into the diaphragm may cause hepatobronchial fistula. 4. Pulmonary Amebiasis - Often secondary to liver abscess rupture through the diaphragm. - Symptoms:Severe pleuritic chest pain. - Dyspnea and nonproductive cough. - Chocolate-brown sputum (from hepatobronchial fistula). - Less commonly, direct hematogenous spread from the colon bypassing the liver. 5. Metastatic Amebiasis - Rare systemic involvement of organs: Kidney, brain, spleen, adrenal gla