Plasmodium Species - Malaria


Indications for Testing

  • Clinical history and symptoms with residency in or travel to endemic area

Laboratory Testing

  • Diagnosis information (CDC)
  • Giemsa-stained blood smear (300 oil-immersion fields examined)
    • Demonstration of intraerythrocytic parasites is diagnostic
    • Specimen should be collected when patient's temperature is rising
    • Single specimen insufficient to rule out malaria
    • Detection threshold – 4-100 parasites/µL
    • Less sensitive in low-level parasitemia, partial immunity, partially treated patients, and in patients with malaria caused by Plasmodium species other than P. falciparum
  • Malaria antibody testing
    • Not useful in acute disease, but IgG response is rapid
    • Provides evidence of past exposure
    • Does not provide definitive identification of Plasmodium spp
  • Rapid antigen testing (eg, ParaHIT, MakroMed, HRP-II ELISA, BinaxNOW Malaria)
    • Most useful in rapid diagnosis or exclusion of P. falciparum
    • CDC recommends follow-up confirmation of rapid testing for U.S. patients
  • PCR
    • Many available platforms
      • Qualitative platforms cannot be used to monitor treatment
  • Other nucleic acid testing
    • High sensitivity and specificity
    • Accuracy of quantification of parasitemia depends on platform
    • Not readily available

Differential Diagnosis

Clinical Background

Malaria is caused by the protozoan parasite Plasmodium and is transmitted by infected mosquitos.


  • Incidence
    • Worldwide distribution in tropical areas – endemic in >95 countries
      • 3.4 billion people (half of world’s population) are at risk each year
      • ~207 million new cases reported every year
      • 627,000 deaths from malaria annually worldwide
  • Transmission
    • Vector – Anopheles mosquito


  • Most malarial infections in humans are caused by the following species of Plasmodium parasites
    • P. vivax – mostly in Asia, Latin America, and some regions of Africa; most prevalent species because of human population densities, especially in Asia
    • P. falciparum – causes most severe form of malaria, including death; found in all tropical and subtropical regions, predominates in Africa
    • P. ovale – mostly in western Pacific islands and Africa, especially West Africa
    • P. malariae – in all tropical and subtropical regions
    • P. knowlesi – Southeast Asia

Risk Factors

  • Children <5 years
  • Pregnancy – women are most vulnerable during first pregnancy
    • Fetus is also at risk
  • Refugees from endemic countries
  • Nonimmune travelers to endemic areas


  • Characteristic malarial symptoms result from parasite-infected red blood cells that may accumulate and sequester in various organs, including heart, brain, lungs, and kidneys

Clinical Presentation

  • May be nonspecific flu-like presentation – malaise, fever, myalgias
    • Typically occurs 7-30 days after mosquito bite
  • Progresses to splenomegaly, anemia, jaundice
  • Severe infection, usually from P. falciparum species, may cause the following
  • Dormant infections can occur with P. vivax and P. ovale
    • Recurrence most common with P. vivax
  • Complications in infected pregnant women
    • Spontaneous abortion
    • Preterm labor
    • Low birth weight
    • Congenital infection – fever, hepatosplenomegaly, jaundice, anemia

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
Parasites Smear (Giemsa Stain), Blood 0049025
Method: Stain

Detect blood parasites, including species of Plasmodium, Babesia, microfilaria and trypanosomes

Travel history required

Use to detect blood spirochetes (eg, relapsing fever Borrelia spp)

Blood collection during fever usually yields highest parasite numbers


Sequential blood samples may be required for diagnosis due to cyclical nature of disease

Malaria, Rapid Screen and Giemsa Stain 2001547
Method: Qualitative Immunochromatography/Stain

Screen for malaria

Travel history required

Rapid screen does not detect parasitemia less than 0.5%

Rapid screen should not be used for therapeutic monitoring

All rapid antigen test results are confirmed by blood smear examination

Malaria Antibody, IgG 0051356
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Retrospectively diagnose malaria in patients from non-endemic areas with relevant exposure and prior symptoms

Do not use to diagnose malaria in symptomatic patients

False-positive results may be seen in up to 18% of patients positive for antinuclear antibodies or rheumatoid factor

Serological results from this assay alone should not determine diagnosis

Malaria Detection and Speciation, Qualitative by Real-Time PCR 2004963
Method: Qualitative Real-Time Polymerase Chain Reaction

Use only to determine malaria species

Do not use to monitor treatment

Detection of asymptomatic parasitemia in individuals from malaria-endemic areas is possible; therefore, use only in conjunction with patient travel history and symptoms consistent with malaria

Latent-phase hypnozoites of P. ovale and P. vivax may not be detected