1. Introduction Malaria is a life-threatening disease caused by protozoan parasites of the genus Plasmodium , transmitted to humans through the bite of infecte
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 → 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 → Chloroquine Severe Malaria (IV Treatment) - IV Artesunate (preferred) or IV Quinine - Supportive Care → Fluids, blood transfusion, glucose monitoring 9. Prevention and Control - Vector Control Insecticide-treated nets (ITNs) - Indoor residual spraying (IRS) - Larval source reduction - Chemoprophylaxis Mefloquine , Doxycycline , Atovaquone-proguanil - Vaccination RTS,S/AS01 (Mosquirix) → Partial protection 10. Critical Notes & Exam Tips - P. falciparum causes severe malaria due to cytoadherence . - Hypnozoites in P. vivax/P. ovale cause relapses . - Cerebral malaria = P. falciparum , due to sequestration in brain capillaries . - Primaquine is the only drug that clears hypnozoites . Remember: Malaria control = Vector control + Treatment + Prevention . Malaria: Immunity, Diagnosis, Treatment, and Control Immunity in Malaria Malaria immunity can be classified into innate immunity and acquired immunity . 1. Innate Immunity Innate immunity is due to genetic and physiological factors that provide natural resistance to malaria infection. These include: - Duffy-negative RBCs : Individuals lacking the Duffy blood group antigen (Fya and Fyb alleles) are resistant to Plasmodium vivax infection. - Nature of hemoglobin :Hemoglobin E provides protection against P. vivax . - P. falciparum does not multiply efficiently in sickled red blood cells (HbS). - Fetal hemoglobin (HbF) in neonates protects against all Plasmodium species. - G6PD deficiency : Common in Mediterranean, African, Middle Eastern, and Indian populations, it offers some resistance to malaria. - HLA-B53 : This human leukocyte antigen (HLA) is associated with protection from malaria. - Nutritional status :Severe malnutrition and iron deficiency may confer some protection against malaria. - However, iron supplementation in pregnancy may enhance susceptibility to P. falciparum . - Pregnancy : Malaria is more severe in pregnant women, especially primigravida (first-time pregnancies). - Splenectomy : The spleen plays a critical role in immunity against malaria. Individuals without a spleen (splenectomy) are more susceptible. 2. Acquired Immunity Acquired immunity develops after repeated exposure to malaria infection and is mediated by both humoral and cellular immunity . - Partial protection : Acquired immunity provides partial protection, preventing severe disease but not eliminating parasites. - Premunition : This refers to the state where low levels of the parasite persist in the body, providing continuous immune stimulation and protection from superinfection. - Humoral immunity :Antibodies against asexual blood forms inhibit red cell invasion and parasite growth. - Antibodies against sexual stages reduce malaria transmission. - Maternal antibodies : Passive immunity is provided to newborns via maternal antibodies. - Young children : Highly susceptible due to lack of prior exposure and immature immune systems. Diagnosis of Malaria Diagnosis of malaria involves laboratory and clinical assessments. Laboratory Diagnosis - Microscopy (Gold sta