In areas of Ghana where malaria is endemic, the predominant Plasmodium
species is P. falciparum
, thus making it an important cause of severe malaria. Early treatment is a key measure in the management of severe malaria, but to ensure correct treatment, early and definitive diagnosis must be available (3
). Giemsa-stained thick blood film microscopy has historically been the mainstay of laboratory diagnosis and continues to be the gold standard despite its disadvantages (10
). As a result of these limitations, alternative techniques for the diagnosis of malaria that are easy and quick to perform as well as cheaper need to be evaluated.
The study results show comparable performance characteristics between the PM and GS. The PM detected 4 more positive malaria cases than GS. The PM uses a sensitive fluorescent dye, 4′,6-diamidino-2-phenylindole (DAPI), which strongly binds to intracellular double-stranded DNA (dsDNA) of the malaria parasite if it is present in the erythrocytes. False-positive PM results might be explained by the presence of fragmented nuclei from damaged reticulocytes or white blood cells. Also, the presence of bacterial or other microbial DNA as well as other nonspecific fluorescent artifacts might be misinterpreted as plasmodial dsDNA. Most of the possible nonplasmodial fluorescence signals may be identifiable. We observed that plasmodial DNA staining by DAPI produced brighter fluorescence than nonplasmodial DNA staining, and for confirmation of parasite localization within the erythrocyte, the PM microscope can be easily switched from fluorescence to bright field and back. The PM also generated two false-negative results. These could have been the result of the low level of parasitemia in blood films, as shown by the late RT PCR CT
values (28.1 and 27.6, respectively). Milne et al. (16
) reported that most routine diagnostic laboratories generally achieve a lower level of sensitivity of detection (average, 0.01% RBCs infected; 500 parasites/μl) in the examination of blood films than that found by Gilles (10
) under optimal conditions, for which the sensitivity of thick-film microscopy is 10 to 30 parasites/μl of blood (10
); thus, lower parasite concentrations may not be detected by even the best expert microscopist. Semi-immune parasite carriers with low levels of parasitemia may also have had false-negative results. GS has been shown to be the less-sensitive test used as a reference method (6
); nevertheless, it is cheap and can be used for both qualitative and quantitative purposes and is the only cheap method that can be used for species identification (6
). RT PCR has been reported to have 100% sensitivity and specificity (4
) and an analytical sensitivity of 0.01 to 0.02 parasites/μl (14
). RT PCR appears to be a useful method for detecting Plasmodium
parasites in active malaria surveillance (6
), even though DNA may persist for up to 8 days posttreatment (12
). However, it is impossible to use it in rural areas of malaria endemicity due to its cost, sophistication, and labor intensiveness.
The PM has diagnostic abilities comparable to those of the GS but has various advantages. (i) Only a small amount of blood is needed, making it ideal for child patients. (ii) It is less labor intensive and faster to use and therefore has a better turnaround time than the GS and requires very little training and expertise. Furthermore, there is no need for reagent preparation, as reagents are already dried on the slides, which may also prolong the shelf life of the test reagents. (iii) The PM test is battery operated, making it ideal for field work and areas where there is no electricity. (iv) The PM is cheaper to use (Table ). However, the test is not suited for species differentiation. In the study area, about 99% of malaria infections are due to P. falciparum
(unpublished data of the Biostatistics Dept, Agogo Presbyterian Hospital). P. falciparum
also predominates in most areas of West Africa where malaria is endemic (8
); thus, distinction between species is of less concern in the study area. P. malariae
and P. ovale
were each detected in only one sample by GS and RT PCR. These two samples were also positive by the PM, which shows that the PM is able to detect about 1% of non-P. falciparum
malaria in the study area and areas where other species of malaria coexist at high frequencies. It may not be possible to store blood slides for an expanded period. However, sealing the ends of the coverslip with wax can enable the slides to be stored for a considerable period of time.
The PM represents an alternative method for GS in less-developed areas where malaria is endemic. More-sensitive tests such as RT PCR should be used at reference laboratories and institutions to further enhance diagnosis and reduce inappropriate treatment and eventual drug resistance.