Study Trypanosoma with clear, structured coverage of the key concepts in Parasitology. Designed for MBChB students preparing for medical examinations.
TRYPANOSOMA OVERVIEW Type : Protozoan parasite (hemoflagellate) Kingdom : Protista Phylum : Sarcomastigophora Class : Zoomastigophora Order : Kinetoplastida Family : Trypanosomatidae GENERAL CHARACTERISTICS Elongated, motile parasites with undulating membrane Single flagellum arising from kinetoplast Kinetoplast contains mitochondrial DNA Polymorphic (different forms in different hosts) Obligate parasites requiring two hosts for complete life cycle MAIN SPECIES AND DISEASES 1. T. brucei gambiense → West African Sleeping Sickness (WASS) 2. T. brucei rhodesiense → East African Sleeping Sickness (EASS) 3. T. cruzi → Chagas Disease (American Trypanosomiasis) --- AFRICAN TRYPANOSOMIASIS (SLEEPING SICKNESS) CAUSATIVE AGENTS T. brucei gambiense and T. brucei rhodesiense MORPHOLOGY Length : 15-30 μm Width : 1.5-3.5 μm Shape : Elongated with pointed ends Flagellum : Single, arising from kinetoplast Undulating membrane : Present along body length Nucleus : Central, oval Kinetoplast : Near posterior end LIFE CYCLE - SIMPLE STEPS IN HUMAN HOST: Infection : Metacyclic trypomastigotes injected by tsetse fly bite Multiplication : Parasites multiply in lymphatic system Blood invasion : Transform into slender blood trypomastigotes Tissue invasion : Spread to various organs including CNS Antigenic variation : Change surface proteins every 7-10 days IN TSETSE FLY VECTOR: Ingestion : Fly takes blood meal containing trypomastigotes Midgut development : Transform into procyclic trypomastigotes Migration : Move to salivary glands Transformation : Become epimastigotes, then metacyclic trypomastigotes Transmission : Ready for injection into new host Total cycle time : 3 weeks in vector COMPARISON: T.b. gambiense vs T.b. rhodesiense PATHOGENESIS AND CLINICAL FEATURES STAGE I DISEASE (Systemic - No CNS involvement) Signs & Symptoms: Painless chancre at bite site (trypanosomal chancre) Intermittent fever and chills Rash Anemia and weight loss Headache Hepatosplenomegaly Lymphadenopathy (especially posterior cervical - Winterbottom's sign ) Myocarditis (common in T.b. rhodesiense) Laboratory findings: Anemia Moderate leucocytosis Thrombocytopenia High immunoglobulin M (IgM) levels STAGE II DISEASE (CNS involvement - "Sleeping Sickness") Signs & Symptoms: Increasing headache Mental dullness and apathy Daytime sleepiness Behavioral changes Progressive coma Death from asthenia (weakness) Histopathology: Chronic meningoencephalitis Lymphocytes, plasma cells, and morula cells in meninges Morula cells contain mulberry-shaped IgA masses Perivascular cuffing of brain vessels Neuronal degeneration Microglial proliferation CSF changes: Raised intracranial pressure Pleocytosis (increased WBC) Raised protein levels DIAGNOSIS Non-specific findings: Anemia and monocytosis Raised ESR (due to increased gamma globulins) Reversed albumin:globulin ratio Increased CSF pressure, cells, and proteins Specific diagnosis: Demonstration of trypanosomes in: Peripheral blood Bone marrow Lymph node aspirate CSF Chancre fluid Methods: Microscopy : Wet mount, Giemsa stain Culture : Special media Molecular : PCR Imaging : CT (cerebral edema), MRI (white matter enhancement) TREATMENT STAGE I DISEASE: T.b. gambiense : Pentamidine (3-4 mg/kg IM daily × 7-10 days) T.b. rhodesiense : Suramin (20 mg/kg IV, 5 injections at 5-7 day intervals) Note: Suramin doesn't cross blood-brain barrier but is nephrotoxic STAGE II DISEASE: T.b. gambiense : Eflornithine T.b. rhodesiense : Melarsoprol (Mel-B) 2-3 mg/kg/day (max 40mg) × 3-4 days Note: Melarsoprol crosses blood-brain barrier --- AMERICAN TRYPANOSOMIASIS (CHAGAS DISEASE) CAUSATIVE AGENT Trypanosoma cruzi HOSTS AND VECTORS Definitive host : Humans Vector : Reduviid bugs (triatomine bugs) - "kissing bugs" Reservoir hosts : Armadillo, cats, dogs, pigs MORPHOLOGY Similar to T. brucei but smaller Amastigote form : Oval, 2-4 μm (intracellular) Trypomastigote form : C-shaped, 20 μm (in blood) Epimastigote form : In vector gut LIFE CYCLE - SIMPLE STEPS IN HUMAN HOST: Infection : Metacyclic trypomastigotes from bug feces enter through skin/mucosa Cell invasion : Parasites enter cells and transform to amastigotes Multiplication : Amastigotes multiply in cells Transformation : Become trypomastigotes and rupture cells Blood circulation : Trypomastigotes in bloodstream Tissue invasion : Invade heart, digestive tract, nervous system IN REDUVIID BUG: Ingestion : Bug takes blood meal with trypomastigotes Gut development : Transform to epimastigotes in midgut Multiplication : Epimastigotes multiply Transformation : Become metacyclic trypomastigotes Excretion : Passed in feces during feeding INFECTION CYCLES Sylvatic cycle : Wild animals (armadillos, opossums) Peridomestic cycle : Domestic animals (dogs, cats) Domestic cycle : Humans CLINICAL FEATURES ACUTE CHAGAS DISEASE (1-4 months) Incubation period : 1-2 weeks Age group : Often children under 2 years Chagoma : Subcutaneous lesion at inoculation site Romana's sign : Unilateral, painless peri