Malaria and Plasmodium — Notes OmpathStudy

1. Introduction Malaria is a life-threatening disease caused by protozoan parasites of the genus Plasmodium , transmitted to humans through the bite of infected female Anopheles mosquitoes. The disease is widespread in tropical and subtropical regions and is a major public health concern. 2. Classification of Malaria Parasites Malaria parasites belong to the Phylum Apicomplexa , which consists of intracellular protozoan parasites. They exhibit a structure called the apical complex , used for cell invasion. Medically Important Genera Genus Plasmodium → Causes human malaria Genus Babesia → Causes babesiosis Genus Toxoplasma → Causes toxoplasmosis Subgenera of Plasmodium Subgenus Plasmodium Plasmodium vivax – Benign tertian malaria Plasmodium malariae – Quartan malaria Plasmodium ovale – Benign tertian malaria Subgenus Laverania Plasmodium falciparum – Malignant tertian malaria (most severe) Other Species of Interest Plasmodium knowlesi → Zoonotic malaria (infects macaques and humans) 3. Epidemiology of Malaria The global distribution of malaria varies based on climate, vector presence, and host immunity. Geographical Distribution P. vivax → Common in Asia, North Africa, Central & South America P. falciparum → Predominant in Africa, Papua New Guinea, and parts of Asia P. malariae → Rare, but present in Africa and worldwide in lower prevalence P. ovale → Primarily found in West Africa Classification of Endemicity (WHO Guidelines) Based on spleen/parasite rate in children (2–9 years) : Hypoendemic → <10% spleen/parasite rate Mesoendemic → 11–50% spleen/parasite rate Hyperendemic → 51–75% spleen/parasite rate (seasonal transmission) Holoendemic → 75% spleen/parasite rate (continuous transmission) Vector: Anopheles Mosquito The female Anopheles mosquito transmits the parasite during a blood meal. Breeds in stagnant fresh water (pools, swamps, rice fields). Transmission increases in warm, humid climates. 4. Life Cycle of Plasmodium The life cycle alternates between two hosts: Human (Asexual Phase - Schizogony) Mosquito (Sexual Phase - Sporogony) Asexual Phase (Schizogony) – Human Host Pre-erythrocytic (Liver) Stage Mosquito injects sporozoites into the bloodstream. Within 1 hour , they invade hepatocytes and mature into schizonts . Schizonts rupture after 6–15 days , releasing merozoites into the bloodstream. Erythrocytic (RBC) Stage Merozoites invade red blood cells (RBCs). Develop into trophozoites (ring form) → mature into schizonts → burst, releasing new merozoites. RBC destruction and hemozoin (malaria pigment) accumulation cause clinical symptoms. Gametogony (Sexual Stage in Human) Some merozoites differentiate into gametocytes (male and female forms). Gametocytes circulate in the blood, ready for mosquito uptake. Sexual Phase (Sporogony) – Mosquito Host Gametocyte Uptake Mosquito ingests gametocytes in a blood meal. Fertilization Male microgamete fertilizes female macrogamete , forming a zygote . Zygote matures into an ookinete , which penetrates the mosquito’s gut wall. Sporozoite Formation Ookinete develops into an oocyst , producing sporozoites . Sporozoites migrate to salivary glands , ready for transmission. Extrinsic Incubation Period : 1–4 weeks in mosquito (temperature-dependent). 5. Pathogenesis of Malaria Mechanisms of Disease RBC destruction → Anemia Hemozoin pigment accumulation → Inflammation Cytoadherence (P. falciparum only) → Microvascular blockage → Cerebral malaria Immune response → Release of cytokines (TNF, IL-1, IFN-γ) Pathological Changes Liver → Enlargement, congestion, Kupffer cell hyperplasia Spleen → Enlargement, fibrosis, dark pigmentation Kidneys → Malarial nephropathy, acute renal failure Brain → Congestion, hemorrhages, capillary blockage (cerebral malaria) 6. Clinical Features of Malaria Uncomplicated Malaria Febrile Paroxysm (Occurs in cycles): Cold Stage → Chills, shivering (15-60 min) Hot Stage → High fever (39-41°C), flushed skin (2-6 hours) Sweating Stage → Profuse sweating, temperature drops Cyclic fever patterns : P. vivax/P. ovale → 48-hour cycle (tertian fever) P. malariae → 72-hour cycle (quartan fever) P. falciparum → Irregular fever Severe Malaria (P. falciparum) Cerebral malaria → Coma, seizures, altered consciousness Severe anemia → Hemolysis, low hemoglobin (<5 g/dL) Blackwater fever → Intravascular hemolysis, dark urine (hemoglobinuria) Hypoglycemia → Common in pregnancy and children Renal failure → Acute kidney injury Pulmonary edema → Respiratory distress High mortality if untreated 7. Diagnosis of Malaria Laboratory Tests Blood Smear (Giemsa Stain) → Gold standardThick smear → Detects parasites Thin smear → Identifies species Rapid Diagnostic Test (RDT) → Detects antigens PCR (Polymerase Chain Reaction) → High specificity Serology (ELISA, IFA) → Detects past infections 8. Treatment of Malaria Uncomplicated Malaria P. falciparum → Artemisinin-based combination therapy (ACT) P. vivax, P. ovale → Chloroquine + Primaquine (for hypnozoites) P. malariae → Chloroqui