entamoeba histolytica.pdf

Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 By: Dr: Hussein Wahhab Rabee Divisions of Parasitology: 1. Protozoa 2. Helminthes a. Roundworms (ne...

Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 By: Dr: Hussein Wahhab Rabee Divisions of Parasitology: 1. Protozoa 2. Helminthes a. Roundworms (nematodes) b. Flatworms – Cestodes (tapeworm) Trematode (fluke) 3) Arthropods Protozoa are single-celled organisms that can be found in various environments, including soil, water, and as parasites in other organisms. Some protozoan parasites are significant to human health, causing a variety of diseases. Here are a few notable protozoan parasites: for example 1. Entamoeba histolytica, Disease: Amoebic dysentery Transmission: Contaminated food and water. 2. Plasmodium, Disease: Malaria Transmission: Mosquito bites (Anopheles mosquitoes). 3. Giardia lamblia, Disease: Giardiasis Transmission: Contaminated water. 4. Trypanosoma brucei, Disease: African sleeping sickness, Transmission: Tsetse fly bites. 5. Toxoplasma gondii Disease: Toxoplasmosis, Transmission: Under-cooked meat, contaminated water, or cat feces. individuals and severe complications in immunocompromised individuals. Prevention and Treatment Prevention: Good hygiene, safe drinking water, and controlling insect vectors. Treatment: Varies by disease but can include antiparasitic medications, supportive care, and in some cases, vaccines. 1 Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 Introduction Entamoeba histolytica is a protozoan parasite responsible for amoebic dysentery (amoebiasis). It primarily affects the intestines but can also invade other organs. Taxonomy Kingdom: Protista Phylum: Amoebozoa Class: Tubulinea Order: Amoebida Family: Entamoebidae Genus: Entamoeba Species: E. histolytica Geographic Distribution Pathogenic Entamoeba species occur worldwide and are frequently recovered from fresh water contaminated with human feces. The majority of amebiasis cases occur in developing countries. In industrialized countries, risk groups include men who have sex with men, travelers, recent immigrants, immunocompromised persons, and institutionalized populations. Life Cycle of Entamoeba histolytica The life cycle of Entamoeba histolytica involves multiple stages and can occur in a single host or between different hosts. It primarily includes the following stages: 1. Cyst Stage Infective Form: The cyst is the dormant, resilient form of the parasite, capable of surviving outside the host in contaminated food or water. Transmission: Humans typically become infected by ingesting cysts through the fecal-oral route, often from improper sanitation or contaminated sources. 2. Excystation Location: Once ingested, cysts enter the stomach and travel to the small intestine. Process: In the favorable environment of the intestine, the cysts undergo excystation, releasing trophozoites (the active form). 3. Trophozoite Stage Active Feeding Stage: Trophozoites are motile and actively feed on bacteria and host tissue. 2 Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 Adherence and Invasion: They adhere to the intestinal epithelium using lectins and can invade the intestinal lining, leading to tissue damage and ulcer formation. 4. Multiplication Binary Fission: Trophozoites replicate asexually through binary fission, increasing the number of parasites present in the intestine. 5. Encystation Formation of Cysts: Under adverse conditions (e.g., dehydration or lack of nutrients), trophozoites can encyst, forming new cysts. Survival Mechanism: This stage allows the parasite to survive outside the host until it finds a new host. 6. Excretion Transmission to New Hosts: Cysts are excreted in the feces of infected individuals, continuing the cycle of infection when ingested by others. Summary of the Life Cycle Cysts are ingested through contaminated food or water. Excystation occurs in the small intestine, releasing trophozoites. Trophozoites invade the intestinal mucosa, multiplying and causing disease. Encystation occurs when conditions are unfavorable, forming new cysts. 3 Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 Cysts are excreted in feces, contaminating the environment and allowing for transmissio Asymptomatic Carriage: Many infected individuals show no symptoms. Acute Amoebic Dysentery: Symptoms: Diarrhea (often bloody), abdominal pain, and tenesmus (feeling of incomplete defecation). Extraintestinal Amoebiasis: Can spread to the liver, lungs, and other organs, causing abscesses. Pathogenesis of Entamoeba histolytica Entamoeba histolytica is a protozoan parasite that causes amoebic dysentery and can lead to extraintestinal infections. Its pathogenesis involves several mechanisms that facilitate invasion, tissue damage, and immune evasion. 1. Invasion of Intestinal Mucosa Adherence: E. histolytica trophozoites attach to the epithelial cells of the colon using surface molecules like lectins, which bind to host glycoconjugates. Penetration: Once adhered, trophozoites secrete proteolytic enzymes that degrade the extracellular matrix and facilitate the invasion of the intestinal epithelium. 4 Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 2. Tissue Damage Cytotoxicity: E. histolytica produces various cytotoxic factors, including: Amoebapores: Small proteins that disrupt host cell membranes. Cysteine proteases: Enzymes that contribute to tissue destruction and inflammation. Ulcer Formation: As trophozoites invade the intestinal wall, they cause ulcerations, leading to symptoms such as diarrhea, abdominal pain, and dysentery. Flask shaped ulcers Flask-shaped ulcers resemble bottles or flasks. They develop in the colon's mucosal lining. Linked primarily to Entamoeba histolytica infection. Commonly found in the cecum and ascending colon. These ulcers are relatively deep, penetrating tissues. Margins are irregular and undermined. Inflammation and tissue damage surround ulcer edges. Symptoms include abdominal pain, diarrhea, bloody stools. Severe cases can lead to complications like perforation. Diagnosis involves stool tests and imaging studies. 5 Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 3. Immune Response Modulation Evasion of Host Immunity: E. histolytica can evade the host's immune system through: -Antigenic variation: Changing surface proteins to avoid detection. -Suppressing immune responses: -Inhibiting the actions of immune cells, such as macrophages and lymphocytes. Inflammation: The host's immune response to the infection can lead to significant inflammation, further exacerbating tissue damage and disease symptoms. 4. Extraintestinal Spread Hematogenous Dissemination: In some cases, E. histolytica can enter the bloodstream and spread to other organs, most commonly the liver. Abscess Formation: When it reaches the liver, it can form amoebic liver abscesses, characterized by necrotic tissue and pus. 5. Clinical Manifestations Asymptomatic Carriage: Many individuals can carry E. histolytica without symptoms, allowing the parasite to persist in the population. Symptomatic Infection: Symptoms range from mild diarrhea to severe dysentery, depending on the extent of tissue invasion and immune response. Clinical Diagnosis of Entamoeba histolytica Diagnosing Entamoeba histolytica infections involves a combination of clinical evaluation, laboratory tests, and imaging studies. Here are the key components of the diagnostic process: 1. Clinical History and Symptoms Symptoms: Patients may present with: Diarrhea (often bloody) Abdominal pain and cramping Tenesmus (feeling of incomplete defecation) Fever and weight loss in severe cases Risk Factors: History of travel to endemic areas, consumption of untreated water, or poor sanitation practices. 6 Jabir Ibn Hayyan Medical University College of Medicine Microbiology Department---- MEDICAL PARASITOLOGY -------------- Lec:2- 2024 Diagnosis Stool Examination: Microscopic identification of cysts or trophozoites. Serology: Detecting antibodies against E. histolytica. Imaging: Ultrasound or CT scans for abscesses in extraintestinal infections. Treatment Medications: Metronidazole: Commonly used for symptomatic infections. Iodoquinol: Effective for asymptomatic cyst passers. Supportive Care: Rehydration and electrolyte management for severe cases. Prevention Hygiene Practices: Handwashing, safe food preparation, and clean drinking water. Public Health Measures: Sanitation and control of fecal contamination in water sources. Conclusion Entamoeba histolytica remains a significant public health concern in many parts of the world. Continued education and awareness are vital for prevention and control of amoebiasis. 7