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).
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 test is equipped to perform a thick and thin blood smear. Within 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.