Malaria

Cause

Plasmodium species (P. falciparum, P. vivax, P. ovale, P. malariae)

Vector

Female Anopheles mosquito

At risk

• Children (immature immunity)

• Travelers from non-endemic → endemic areas (no immunity)

P. vivax, P. ovale

• 48 hour cycle (tertian)

• Forms hypnozoites → relapse (Dormant liver stage)

P. malariae

• 72 hour cycle (quartan)

• Chronic infection

P. falciparum

• 48 hour cycle (tertian)

• Most severe, fatal, cerebral malaria

Life Cycle of Plasmodium: In Human (Asexual)

1. Exo-erythrocytic (Liver) Stage

2. Erythrocytic Cycle (Blood Stage)

Exo-erythrocytic (Liver) Stage

• Mosquito injects sporozoites

• Sporozoites travel via bloodstream to liver

• Invade hepatocytes → multiply → form schizont

• Schizont ruptures → merozoites released

2. Erythrocytic Cycle (Blood Stage)

• Merozoites invade RBCs

• Develop:
  Ring stage (immature trophozoite) → trophozoite → schizont

• Schizont ruptures → more merozoites

• Some trophozoites → gametocytes

Life Cycle of Plasmodium: In the Mosquito (Sexual Phase)

• Gametocytes (from human blood) ingested

• Male gametocyte produces 8 microgametes

• Fusion of male + female gametes → zygote (only diploid stage)

• Zygote → ookinete (motile)

• Ookinete → oocyst on midgut wall

• Oocyst → sporozoites (1000+ each)

• Sporozoites migrate to salivary glands

Pathophysiology & Symptoms

• Fever: from synchronized RBC rupture

• Anaemia: due to RBC destruction and suppressed erythropoiesis

• Hypoglycaemia: due to parasite glucose consumption

• ARDS: in severe malaria

• Organ effects:

  • Hepatomegaly (liver enlargement)

  • Splenomegaly (spleen enlargement)

• Blackwater fever: haemoglobinuria

• Capillary blockage: via cytoadhesion of iRBCs to endothelium

• Immunosuppression: increased risk of sepsis

Diagnosis

Blood smear (Giemsa-stained) to detect and identify Plasmodium species

Treatment: Chemotherapy

• Chloroquine:

  • Enters parasite’s food vacuole (FV)

  • Acidified FV traps CQ → inhibits haemozoin formation

  • Free haem is toxic → kills parasite

• Chloroquine resistance is widespread

Treatment: Vaccination

RTS,S/AS01: approved for use in children in high-P. falciparum transmission regions

Prevention

• Take antimalarials for a few weeks after leaving endemic area

• Use of mosquito nets, repellents, and vector control

Transmission routes

• Mosquito bite (most common)

• Airport malaria: mosquito travels by plane

• Blood transfusion

• Shared needles

• Congenital (mother → baby)

• Introduced malaria: local mosquitoes bite infected traveler