Plasmodium Species - Malaria

Malaria is caused by the protozoan parasite Plasmodium and is transmitted by infected mosquitos. Intraerythrocytic parasites on Giemsa stain is diagnostic. Rapid antigen testing is also frequently used; the CDC recommends following up any positive results with confirmatory testing.

Diagnosis

Indications for Testing

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

Laboratory Testing

  • Plasmodium testing and 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 patients with malaria caused by Plasmodium species other than P. falciparum
  • Rapid antigen testing (eg, ParaHIT, MakroMed, HRP-II ELISA, BinaxNOW Malaria)
    • Most useful in rapid diagnosis or in exclusion of P. falciparum
    • CDC recommends follow-up confirmation of rapid testing for U.S. patients
  • Polymerase chain reaction (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

Background

Epidemiology

  • Incidence –  worldwide distribution in tropical areas; endemic in >95 countries (CDC, 2016)
    • 3.2 billion people (half of world’s population) are at risk each year
    • ~214 million new cases reported every year
    • 438,000 deaths from malaria annually worldwide
    • ~1,500 cases in U.S. annually
  • Transmission – vector (Anopheles mosquito)

Organism

  • 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 – in all tropical and subtropical regions, predominates in Africa; causes most severe form of malaria, including death
    • P. ovale – mostly in western Pacific islands and Africa (especially West Africa)
    • P. malariae – in all tropical and subtropical regions; only plasmodium with quartan cycle
    • 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

Pathophysiology

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
  • Dormant infections can occur with P. vivax and P. ovale – recurrence most common with P. vivax
  • Complications in infected pregnant women
    • Infection in mother can be more severe
    • Spontaneous abortion
    • Preterm labor
    • Low birth weight
    • Congenital infection – fever, hepatosplenomegaly, jaundice, anemia

ARUP Laboratory Tests

Screen for and detect spirochetes and blood parasites, including microfilaria, Babesia, Trypanosoma, and Plasmodium species

Travel history required

Time sensitive

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

Not a first-line test for malaria screening; refer to parasite smear or malaria rapid screen and Giemsa stain for screening and diagnosing acute disease

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

Medical Experts

Contributor

Couturier

Marc Roger Couturier, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories
Contributor

References

Additional Resources
  • Wintrobe's Clinical Hematology

    Greer JP, Arber DA, Glader B, et al. Wintrobe’s Clinical Hematology, 13th ed. Philadelphia: Lippincott Williams and Wilkins, 2013.

    Book
  • CDC - Malaria

    U.S. Department of Health and Human Services, Centers for Disease Control and Prevention. Parasites - malaria. [Last Reviewed: Dec 2019; Accessed: Feb 2020]

    Online
  • 23953767

    White NJ, Pukrittayakamee S, Hien TTinh, et al. Malaria. Lancet. 2014; 383 (9918): 723-35.
    PubMed
  • Resources from the ARUP Institute for Clinical and Experimental Pathology®