Preparation of Positive Control from Plasmodium falciparum Culture for Using in Malaria Rapid Diagnostic Test

Malaria is still a major public health problem in many countries including Thailand. There are 6 species of human malaria. Signs and symptoms of malaria infected-patients are non-specific but malaria treatment requires specific antimalarial drugs against each malaria species. If malaria disease is treated incorrectly, the malaria infected-patients will develop severe disease which can cause death, especially with Plasmodium falciparum -infected patients. Therefore, the correct diagnosis is very important. The common laboratory analyses of malaria in the hospital are microscopic examination and malaria rapid diagnostic test (MRDT). The microscopic examination is the standard method. However, this technique requires a highly skilled microscopist to identify the species of malaria. Recently, MRDT has been developed. This is a quick and easy method to detect the histidine-rich protein 2 (HRP-2) and plasmodium lactate dehydrogenase (pLDH) that are the proteins produced by malaria parasites. The quality of MRDT is very important to provide the correct malaria identification. Therefore, the objective of this research was to study the positive control preparation for MRDT from P. falciparum culture. The positive controls were prepared from malaria culture with parasite density 200, 2,000 and 20,000 parasites/µL. These control were stored in different temperatures (25, 4 and -20oC) at different storage times (1, 2, 3 and 4 weeks). Then the malaria parasite were diluted with distilled water at ratio 1:2 followed by the examination with MRDT. The result showed that positive control with parasite density 20,000 parasites /µL gave 100% positive results in all temperatures at all storage durations. Control with malaria parasite density 2,000 parasites/µL gave 100% positive results in all temperatures within 4 weeks. However, positive result of this control was reduced to 83% when stored at 25oC for 4 weeks. For control with malaria density 200 parasites/ µ L 100% positive result was abtained only at -20 o C when stored for 1, 2 and 3 weeks. At 4 weeks  storage time the positive result was reduced to 67%. The positive result was reduced with higher storage temperature and longer storage duration. The results provide an optimal parasite density of 20,000 parasites/µL that gives 100% positive result in all storage temperature and all storage duration as positive control preparation for MRDT.