Malaria:

## **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** → Ac