Malaria

Overview – Malaria

Malaria is a life-threatening protozoan infection caused by Plasmodium species, transmitted by female Anopheles mosquitoes. It remains a major global health concern, particularly in tropical and subtropical regions, with Plasmodium falciparum responsible for the most severe and fatal cases. Clinical features range from cyclical fevers to severe multi-organ dysfunction, and diagnosis and treatment must be timely to prevent complications and mortality.

Definition

Malaria is a parasitic disease caused by infection with Plasmodium protozoa, transmitted through the bite of an infected female Anopheles mosquito. It causes recurrent fever, anaemia, and may lead to life-threatening complications.

Aetiology

  • Pathogen: Plasmodium (eukaryotic protozoan)
  • Species:
    • P. falciparum – Most serious (not persistent in liver)
    • P. vivax – Less serious, persistent in liver
    • P. ovale – Less serious, persistent in liver
    • P. malariae – Less serious, not persistent in liver
    • P. knowlesi – Zoonotic, less common

Vector

  • Anopheles mosquito
    • Bites at night
    • Breeds in shaded, vegetated, permanent water sources

Transmission Patterns

  • Stable transmission: Continuous, endemic transmission
  • Unstable transmission: Periodic epidemics, often following environmental changes

Lifecycle

  1. Mosquito bites infected human → ingests gametocytes
  2. Gametocytes → oocysts in mosquito gut → rupture → sporozoites
  3. Sporozoites migrate to mosquito’s salivary glands
  4. Sporozoites injected into new human host
  5. Sporozoites infect liver → multiply into merozoites
  6. Merozoites enter RBCs → cycle of replication and lysis
  7. Some merozoites become gametocytes → re-ingested by mosquitoes
MALARIA
https://www.cdc.gov/dpdx/malaria/index.html

Incubation Period

  • Ranges from 2 weeks to several months depending on species and host immunity

Pathogenesis

  • Red blood cell lysis → Pyrogens → cyclical fever
  • Extravascular haemolysis (spleen) → Anaemia, haemoglobinuria
  • Cytoadherence: RBCs become sticky → capillary blockage → hypoxia → multiorgan failure
    • Cerebral malaria, pulmonary oedema, renal failure
  • Immune complex deposition (Type III hypersensitivity) → arthritis, glomerulonephritis

Clinical Features

Uncomplicated Malaria (e.g. P. vivax, P. ovale):

  • Episodic fever (tertian/quartan pattern)
  • Headache, vomiting, diarrhoea
  • Chills, sweating
  • Muscle aches, dry cough
  • Splenomegaly, jaundice
  • May relapse due to liver hypnozoites
  • Treatment: Primaquine (targets liver hypnozoites)

Complicated (Severe) Malaria – P. falciparum:

  • Severe headache, nausea, vomiting
  • Cerebral ischaemia, hallucinations, seizures, coma
  • Severe anaemia (Hb 10–20 g/L), haemoglobinuria, renal failure
  • Hepatosplenomegaly, hypoglycaemia, acidosis
  • High fatality if untreated
  • Treatment: Artemisinin derivatives (target blood-stage gametocytes)

Investigations

  • Clinical suspicion: Endemic area + classic symptoms
  • Microscopy: Thick and thin blood films (Giemsa stain)
  • RDTs (Rapid Diagnostic Tests): Detect Plasmodium antigens
  • PCR: High-sensitivity molecular diagnosis

Management

Gametocidal Agents

  • Artemether/lumefantrine: First-line for P. falciparum
  • Single-dose primaquine: Clears gametocytes

Hypnozoite-targeting Agents

  • Primaquine: Prevents relapse in P. vivax and P. ovale infections

Supportive Care (for severe cases):

  • Fluids and electrolytes
  • Glucose monitoring (risk of hypoglycaemia)
  • Management of seizures and coma

Prevention

  • Chemoprophylaxis: For travellers (e.g. doxycycline, atovaquone-proguanil)
  • Mosquito control: Nets, repellents, indoor residual spraying
  • Environmental: Vector habitat reduction
  • Vaccines: Some in development with partial protection

Immunity

  • Acquired immunity: After repeated exposures (common in endemic areas)
  • At-risk populations:
    • Non-immunes (infants, travellers, pregnant women) → High severity risk
    • Immunity is lost after extended absence from endemic zones

Genetic Protection

  • Sickle cell trait: Infected cells rupture prematurely → less parasite replication
  • Duffy antigen absence: Confers resistance to P. vivax
  • G6PD deficiency, thalassemia: Partial protective effects

Summary – Malaria

Malaria is a protozoan parasitic disease caused by Plasmodium species and transmitted via Anopheles mosquitoes. It presents with episodic fevers and may progress to life-threatening complications, especially in P. falciparum infections. Management includes antimalarial agents such as artemisinin and primaquine, with prevention focused on vector control and prophylaxis. For a broader context, see our Microbiology & Public Health Overview page.

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