Malaria

Description

• Protozoan infection transmitted through the Anopheles mosquito
• Incubation period 8–16 d
• Periodicity of the disease is due to the life cycle of the protozoan:
  • Exoerythrocytic phase: Immature sporozoites migrate to liver, where they rapidly multiply into mature parasites (merozoites)
  • Erythrocytic phase: Mature parasites are released into circulation and invade RBCs
  • Replication within RBCs followed 48–72 hr later by RBC lysis and release of merozoites into circulation, repeating cycle
  • Fever corresponds to RBC lysis
• Plasmodium falciparum:
  • Cause of most cases and almost all deaths
  • Usually presents as an acute, overwhelming infection
  • Able to infect red cells of all ages:
    • Results in greater degree of hemolysis and anemia
  • Causes widespread capillary obstruction:
    • Results in end-organ hypoxia and dysfunction
  • More moderate infection in people who are on or who have recently stopped prophylaxis with an agent to which the P. falciparum is resistant
  • Post-traumatic immunosuppression may cause relapse of malaria in patients who have lived in endemic areas
• Plasmodium vivax and Plasmodium ovale:
  • May present with an acute febrile illness
  • Dormant liver stages (hypnozoites) that may cause relapse 6–11 mo after initial infection
• Plasmodium malariae:
  • May persist in the bloodstream at low levels up to 30 yr

Etiology

• Transmission usually occurs from the bite of infected female Anopheles mosquito
• North American transmission possible:
  • Anopheles mosquitoes on east and west coasts of the U.S.
  • Transmission may also occur through infected blood products and shared needles

• Sickle cell trait protective
• Cerebral malaria more common in children
• In highly endemic areas with minimal lab capability, all children presenting with febrile illness may be treated