Novel Test Diagnoses Malaria in Returning Travelers

A novel, single-amplification polymerase chain reaction (PCR) assay has been used to diagnose malaria among travelers returning from endemic areas.

A practical single-round amplification Plasmodium-genus-specific PCR assays has been designed that is based on primers targeting the 18S locus and the mitochondrial genome with sensitivity and specificity equal to nested PCR.

Tropical disease specialists at the Haukeland University Hospital (Bergen, Norway) carried out a retrospective study of whole blood samples from a cohort of 132 fever patients with potential imported primary or recurrent malaria between 2006 and 2011. The samples had been previously analyzed for malaria parasites on Giemsa-stained, thin and thick slides by experienced microscopists. Three PCR assays, two genus-specific and one species-specific, were assessed in the cohort of patient samples. The mitochondrial PCR products were sequenced in both directions.

Among the 135 samples assayed, 28 were defined as malaria positive by at least two of the methods among microscopy and the three different genus-specific PCR assays. The new mitochondrial PCR was 100% sensitive detecting all 28 positives. At the threshold dilution 0.5 parasites/µL, the sensitivity of the mitochondrial PCR was 97%, that of the single-round, 18S PCR was 93%, and the reference nested 18S was PCR 87%. Both single-round amplification assays identified all malaria positives diagnosed by nested PCR that had a sensitivity of 96%.

Sequencing of the genus-specific mitochondrial PCR products revealed different single nucleotide polymorphisms that allowed species identification of the 28 sequences with following distribution; 20 were Plasmodium falciparum, 6 were P. vivax, 1 was P. ovale, and 1 P. malariae. The microscopists had missed two infections detected by all PCR assays.

The authors concluded that the design of PCR programs with suitable parameters and optimization resulted in simpler and faster single-round amplification assays. Both the sensitivity and specificity of the novel mitochondrial PCR was 100% and proved equivalent to the reference nested PCR. Sequencing of genus-specific mitochondrial PCR products could be used for species determination. The study was published on January 22, 2013, in the Malaria Journal.

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Haukeland University Hospital