Updated: 6/7/2019

Plasmodium

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Snapshot

  • A 25-year-old woman presents to the clinic with a one-week history of continuous high-grade fevers, myalgia, chills, and night sweats. She recently returned to the United States after volunteering with the Peace Corps in Nigeria. Her temperature is 103.2°F (39.6°C) and physical reveals a palpable spleen. A peripheral blood smear is shown.
Introduction
  • Epidemiology
    • geography
      • endemic throughout most of the tropics
      • disproportionately high burden of malaria in Sub-Saharan Africa
    • prevalence
      • WHO estimated 216 million cases of malaria in 91 countries in 2016
    • risk factors
      • exposure to Anopheles mosquitos, particularly at dusk and dawn
  • Pathogenesis
    • transmission
      • through bites of female Anopheles mosquitos
    • Plasmodium life cycle involves two hosts: human and Anopheles mosquito 
      • human host
        • sporozoite stage
          • the Plasmodium-infected Anopheles mosquito inoculates sporozoites into the human host during a blood meal
          • sporozoites infect hepatocytes and mature into schizonts, which rupture and release merozoites  
        • hypnozoite stage
          • for Plasmodium vivax and Plasmodium ovale, a dormant stage (hypnozoites) can persist in the liver and cause relapses
        • merozoite and trophozoite stage
          • merozoites undergo asexual multiplication in erythrocytes
          • merozoites reform to become trophozoites, which are ring-shaped
        • schizont stage
          • trophozoites undergo division to form large multi-nucleated schizonts
          • the schizont ruptures releasing merozoites
            • rupture of erythrocytes correlates with fever spikes
        • gametocyte stage
          • some parasites differentiate into sexual gametocytes, which are the form of the parasite that is ingested by an Anopheles mosquito
      • Anopheles mosquito host
        • oocyst stage
          • male and female gametocytes fuse in the stomach of the mosquito to form an oocyst
        • sporozoite stage
          • the oocyst divides into many sporozoites, which are then inoculated into the human host to begin the cycle anew
    • 4 main speces of Plasmodium cause malaria
      • Plasmodium falciparum 
        • irregular fever patterns
      • Plasmodium vivax
        • 48-hour fever cycle
      • Plasmodium ovale
        • 48-hour fever cycle
      • Plasmodium malariae
        • 72-hour fever cycle
  • Associated conditions
    • occlusion of capillaries in the brain (cerebral malaria), kidneys, and lungs (Plasmodium falciparum)
 Presentation
  • Symptoms
    • fever
    • headache
    • anemia
    • splenomegaly
  • Physical exam
    • palpable spleen
    • conjunctival pallor
Studies
  • Labs
    • Peripheral blood smear shows trophozoites and schizonts within erythrocytes 
      • trophozoite ring form within erythrocyte
      • schizont containing merozoites
      • red granules throughout cytoplasm in erythrocytes seen with Plasmodium vivax and Plasmodium ovale
  • Making the diagnosis
    • most cases are clinically diagnosed
Differential
  • Babesiosis
    • differentiating factor
      • predominantly in northeastern United States
  • Trypanosomiasis
    • differentiating factors
      • lymphadenopathy, somnolence, coma
  • Borrelia recurrentis
    • differentiating factor
      • history of tick exposure
Treatment
  • Medical
    • chloroquine
      • used in areas with low drug resistance
    • mefloquine  
      • used in areas with high rates of chloroquine resistance
    • atovaquone/proguanil or artemether-lumefantrine
      • used in areas with high rates of chloroquine resistance
        • first-line treatment for P. falciparum resistant to chloroquine
    • primaquine
      • used to kill latent hypnozoites in Plasmodium vivax and Plasmodium ovale infection
    • intravenous quinidine or artesunate
      • used in life-threatening situations
Complications
  • Cerebral malaria
    • complication of Plasmodium falciparum infection
    • parasitized erythrocytes occlude capillaries in the brain
  • Renal failure
    • complication of Plasmodium falciparum infection
    • parasitized erythrocytes occlude capillaries in the kidney
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