Plasmodium Species - Malaria

Diagnosis

Indications for Testing

  • Clinical history and symptoms with residency 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
    • Should be collected when patient's temperature is rising
    • Single specimen insufficient to rule out malaria
    • Detection threshold 4-100 parasites/µL
  • 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-2 assays, BinaxNOW® malaria)
    • Most useful in rapid diagnosis or exclusion of P. falciparum
    • CDC recommends follow-up confirmation of rapid testing for U.S. patients
  • Nucleic acid testing
    • Very sensitive and specific
    • Ability to accurately quantify parasitemia depends on platform

Differential Diagnosis

Clinical Background

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

Epidemiology

  • Incidence
    • Worldwide distribution in tropical areas – endemic in >95 countries
      • >500 million cases reported every year
  • Transmission
    • Vector – Anopheles mosquito

Organism

  • Most malarial infections in humans are caused by the following 
    • P. vivax (most common)
    • P. falciparum (most severe)
    • P. ovale
    • P. malariae
    • P. knowlesi

Risk Factors

  • Children <5 years
  • Pregnant women (most vulnerable in first pregnancy)
  • Refugees from endemic countries
  • Nonimmune travelers in 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 pregnant patients
    • Spontaneous abortion
    • Preterm labor
    • Low birth weight
    • Congenital infection – fever, hepatosplenomegaly, jaundice, anemia

Treatment

  • Success of drug treatment depends on several factors, including Plasmodium species, drug-resistance patterns, clinical condition of patient, and drug allergies

Prevention

  • Personal protection measures
    • Use repellents containing DEET or picaridin
    • Avoid outdoor activities during mosquito feeding times (dusk to dawn)
    • Wear appropriate clothing for protection from mosquito bites
  • Prophylaxis for travel to endemic countries is usually successful in the following scenarios
    • Appropriate drugs are selected for area visited
    • Patient compliance

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

Diagnose acute malaria

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

Confirm positive ELISA result for malaria antibodies

Travel history required

Blood collection during fever usually yields highest parasite numbers

Time sensitive

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 a previously non-immune individual

Screen for chronic malaria

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

Serologic 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