Updated: 12/19/2019

Malaria

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Snapshot

  • A 36-year-old man presents to the clinic with a 2-week history of cyclic high-grade fevers, myalgia, chills, and night sweats. When asked about recent travel, he notes that he had been visiting his family in Ghana in the month prior to the onset of his symptoms. He is started on a treatment regimen of quinidine in combination with doxycycline.

 

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 2 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 species 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 erythrocyte cytoplasm 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 
      • used in areas with high rates of chloroquine resistance
    • 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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Questions (2)
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(M2.ID.15.42) A 25-year-old medical student is doing an international health elective in the Amazon River basin studying tropical disease epidemiology. As part of his pre-trip preparation, he wants to be protected from malaria and is researching options for prophylaxis. Which of the following agents should be avoided for malarial prophylaxis in this patient?

QID: 104927
1

Chloroquine

32%

(8/25)

2

Mefloquine

8%

(2/25)

3

Atovaquone-proguanil

8%

(2/25)

4

Doxycycline

28%

(7/25)

5

Quinine

20%

(5/25)

M 7 E

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