Malaria Rapid Test Evaluated in Low Transmission Area

Light microscopy detecting human malarial parasites in Giemsa-stained thick and thin blood films still remains the gold standard for malaria diagnosis. In many peripheral health centers of endemic countries, microscopy is not available due to limited resources or lack of expertise.

Malaria rapid diagnostic tests (RDTs), based on immunochromatographic parasite antigen detection, are of great value in endemic regions. However, it remains unclear whether RDTs are useful in field conditions in low transmission areas since their reliability is limited by the lack of detection of low-density parasitemia.

Scientists at Cheikh Anta Diop University (Dakar, Senegal) enrolled 215 patients suspected of malaria in two peri-urban area of Dakar. Blood samples were collected for RDT and microscopy, and a filter paper collected for polymerase chain reaction (PCR). Inclusion criterion for this study was individuals with fever and suspicion of malaria and without clinical sign of severe malaria.

The team made both thick and thin films were made in the same slide which were stained and examined. Finger prick blood sample were tested for malaria parasites using CareStart Malaria HRP2/pLDH Combo Test in the field. CareStart RDT is an immunochromatographic test coated with monoclonal antibodies in two separate bands, one recognizing the specific histidine-rich protein-2 (HRP-2) associated with the presence of Plasmodium falciparum and the other detecting presence of pan malaria-specific antigen (pLDH) of all malarial parasites species. The real-time PCR assay, known as photo-induced electron transfer (PET)-PCR, was also performed.

The investigators reported that when considering PCR as the gold standard, CareStart RDT showed high sensitivity (97.3%) and specificity (94.1%) with a positive predictive value (PPV) and negative predictive value (NPV) of 97.3% and 94.1%, respectively. Microscopy had a sensitivity of 93.2% and specificity of 100%, and PPV and NPV of 100% and 87.2%, respectively. CareStart RDT showed less false negative but more false positive results compared to microscopy.

The authors concluded that although RDT usefulness in low transmission areas or in the detection of low parasite density infections is being questioned, CareStart RDT showed good sensitivity comparable to that performed by expert microscopist. However, in the wake of reported HRP2 deletion in other countries, microscopy should always accompany the use of RDT. Combination of RDT and microscopy together with the evaluation of malaria RDTs over time should be a powerful tool for diagnosing malaria in endemic countries. The study was published on August 10, 2017, in the Malaria Journal.

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Cheikh Anta Diop University