Once malaria is suspected on clinical grounds, it is mandatory to obtain the laboratory confirmation of the presence of malaria parasites in the patient’s specimen, whenever possible.
Blood is taken by pricking a finger or ear lobule before starting treatment with antimalarials. Blood for smear should be collected late in the febrile paroxysm (a few hours after the height of paroxysm) to coincide with presence of highest number of malarial parasites in the peripheral blood.
The diagnosis of malaria may in fact be pursued by the direct demonstration of the parasite whole cell or of parasite’s nucleic acid or products in the blood (direct diagnosis) or by the demonstration of the patient’s immune response to the infection (indirect diagnosis or immunodiagnosis).
The direct demonstration of the whole parasitic cell may be accomplished by several methods, from the old and simple (but still gold standard!) direct microscopic observation of stained blood specimens to the more recent and sophisticated concentration and staining techniques (buffy coat preparation, Quantitative Buffy Coat (QBC), acridine orange method).
Finally, the detection of the presence of the genome of the parasite is now possible by the use of the polymerase chain reaction (PCR) technique. The evidence of specific antibodies is of little, if any, diagnostic value in endemic areas but may provide important information in epidemiological studies and in some selected settings such as blood donor screening.
Rapid and accurate diagnosis of malaria is integral to the appropriate treatment of affected individuals and in preventing the further spread of infection in the community.
a. Microscopy and staining methods
Microscopic examination remains the “gold standard” for laboratory confirmation of malaria. Microscopy is an established, relatively simple technique that is familiar to most laboratorians. Any laboratory that can perform routine hematology tests is equipped to perform a thick and thin blood smear. Within a few hours of collecting the blood, the microscopy test can provide valuable information.
Blood specimen collected from the patient is spread as a thick or thin blood smear, stained with a Romanovsky stain (most often Giemsa), and examined with 100x oil immersion objective. Visual criteria are used to detect malaria parasites and to differentiate (when possible) the various species.
Once the diagnosis is established, usually by detecting parasites in the thick smear, the thin smear can be examined to determine the malaria species and the parasitemia, or the percentage of the patients’ red cells that are infected with malarial parasites.
Finished reading? Now, it is a quiz time: Test your understanding of Malaria life cycle, pathogenesis and diagnosis