Plasmodium Species

Indications for Testing

Clinical history and symptoms with residency or travel to endemic area

Laboratory Testing

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

Newborns
Pregnant females
- Sepsis
- Congenital infection with agents such as parvovirus
Adults (nonpregnant)

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
- Cerebral encephalopathy
- Hypoglycemia
- Hypotension
- Liver dysfunction
- Acute renal failure, blackwater fever
- Disseminated intravascular coagulation
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

Tests generally appear in the order most useful for common clinical situations

Test name: Parasites Smear (Giemsa Stain), Blood

ARUP #: 0049025

Methodology: Stain

Use:

Diagnose acute malaria

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

Confirm positive ELISA result for malaria antibodies

Travel history required

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

Test name: Malaria, Rapid Screen (Includes Giemsa stain 0049025)

ARUP #: 2001547

Methodology: Qualitative Immunochromatographic Assay/Stain

Use:

Screen for malaria

Travel history required

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

Test name: Malaria Antibody, IgG

ARUP #: 0051356

Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Use:

Retrospectively diagnose malaria in a previously non-immune individual

Screen for chronic malaria

Limitations:

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

Test name: Malaria Detection and Speciation, Qualitative by Real-Time PCR

ARUP #: 2004963

Methodology: Qualitative Real-Time Polymerase Chain Reaction

Use:

Use only to determine malaria species

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

ARUP Institute for Clinical and Experimental Pathology®

Fisher, Mark A., PhD. Medical Director, Bacteriology and Antimicrobials at ARUP Laboratories; Assistant Professor of Pathology, University of Utah

Comprehensive Review: August 2011
Last Update: August 2011

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