Quantitative real-time polymerase chain reaction PCR (qPCR) on blood samples is more sensitive than thick film microscopy for malaria diagnosis.

The molecular method can be used to determine the parasitemia of African children infected with Plasmodium falciparum in both plasma and whole blood samples and has been compared with microscopic techniques.

Scientists at the University of Oxford (Headington, UK) working with an international team conducted a double-blind randomized placebo-controlled trial in Southern Mozambique from September 2005 to March 2009. Study participants were followed up until age 24 months. Blood slides were read to quantify parasitemia. Plasma samples were stored at -80 °C for three to four years before extraction of DNA. Dried bloodspots collected onto filter paper were stored for the same period at 4 °C with silica gel.

A total of 548 samples were analyzed by qPCR on DNA extracted from whole blood on filter paper (qPCR-blood) and plasma (qPCR-plasma). Of these, 143 (26%) were found to be P. falciparum positive by qPCR-blood, while the qPCR-plasma method detected 37 (7%) as positive. Agreement between both techniques was 78.1%. Parasite infection detected by microscopy showed greater agreement with detection by qPCR-plasma (96.85%) than did qPCR-blood (69.7%). However, qPCR-blood detected parasitemia in approximately 3.5 fold more samples than qPCR-plasma or thick film microscopy.

The authors concluded that qPCR using parasite DNA from whole blood is more sensitive to detect submicroscopic levels of parasitemia than using parasite DNA from plasma. However, the data demonstrated that the performance of qPCR on plasma samples is similar to the performance of microscopy, suggesting that qPCR on plasma can be used as a substitute to microscopy when performing retrospective studies with limited material and when blood smears are unavailable. This approach, together with developments in the use of loop-mediated isothermal amplification may assist in making molecular detection of malaria infection in the field more common. The study was published on June 15, 2012, in the Malaria Journal.

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