Plasmodium Species - Malaria

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

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

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

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 – found 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 the following
  • 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
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.

Parasites Smear (Giemsa Stain), Blood 0049025
Method: Stain

Limitations 

Blood collection during fever usually yields highest parasite numbers

Time-sensitive

Follow-up 

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

Limitations 

Rapid screen does not detect parasitemia less than 0.5%

Rapid screen should not be used for therapeutic monitoring

Follow-up 

All rapid antigen test results are confirmed by blood smear examination

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

Limitations 

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

Limitations 

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

General References

Baird J. Malaria zoonoses. Travel Med Infect Dis. 2009; 7(5): 269-77. PubMed

Campuzano-Zuluaga G, Hänscheid T, Grobusch MP. Automated haematology analysis to diagnose malaria. Malar J. 2010; 9: 346. PubMed

Collins WE, Jeffery GM. Plasmodium malariae: parasite and disease. Clin Microbiol Rev. 2007; 20(4): 579-92. PubMed

Garcia LS. Malaria. Clin Lab Med. 2010; 30(1): 93-129. PubMed

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

Malaria. Centers for Disease Control and Prevention. [Accessed: May 2016]

Malaria. World Health Organization. Geneva, Switzerland [Accessed: Nov 2015]

Murray CK, Gasser RA, Magill AJ, Miller S. Update on rapid diagnostic testing for malaria. Clin Microbiol Rev. 2008; 21(1): 97-110. PubMed

Rogerson SJ. Malaria in pregnancy and the newborn. Adv Exp Med Biol. 2010; 659: 139-52. PubMed

Rosenblatt JE. Laboratory diagnosis of infections due to blood and tissue parasites. Clin Infect Dis. 2009; 49(7): 1103-8. PubMed

Vasoo S, Pritt BS. Molecular diagnostics and parasitic disease. Clin Lab Med. 2013; 33(3): 461-503. PubMed

White NJ, Pukrittayakamee S, Hien TT, Faiz A, Mokuolu OA, Dondorp AM. Malaria. Lancet. 2014; 383(9918): 723-35. PubMed

Wilson ML. Laboratory diagnosis of malaria: conventional and rapid diagnostic methods. Arch Pathol Lab Med. 2013; 137(6): 805-11. PubMed

References from the ARUP Institute for Clinical and Experimental Pathology®

Petti CA, Polage CR, Quinn TC, Ronald AR, Sande MA. Laboratory medicine in Africa: a barrier to effective health care. Clin Infect Dis. 2006; 42(3): 377-82. PubMed

She RC, Rawlins ML, Mohl R, Perkins SL, Hill HR, Litwin CM. Comparison of immunofluorescence antibody testing and two enzyme immunoassays in the serologic diagnosis of malaria. J Travel Med. 2007; 14(2): 105-11. PubMed

Medical Reviewers

Last Update: August 2016