DIRECT MICROSCOPIC BLOOD
SAMPLE EXAMINATION
The direct microscopic blood sample examination of a patient suffering from “fièvres palustres” allowed the physician Alfonse Laveran in Bone, Algeria, in 1878 to observe the presence of melaniferous white cells and of spherical bodies (red blood cells) of variable volume, containing brown-yellow colored granules (malarial pigment), and later exflagellation in vitro. Besides other considerations, these facts convinced him that parasitic elements were responsible for the malarial fever “fièvres palustres”. Despite this, direct microscopic examination of blood samples is almost always useless because it is generally impossible to recognize malaria parasites by observation of the younger forms; the only easily distinguishable plasmodium stages are those in which the malarial pigment is present (old trophozoites, schizonts, gametocites or forms of these in exflagellation). These older forms exhibit peculiar characteristics of movement, pigment or shape of the infected cell, which can make a tentative diagnosis possible, as for example the typical lively amoeboid motion of P. vivax and its tendency to enlarge and decolorize the host cell, or the “croissant” shape gametocytes of P. falciparum. Sensitivity and specificity of direct microscopic blood examination are therefore very low: on one hand, all the young trophozoites are not detectable by this method, and on the other hand the most mature forms can be masked by the aggregation or the piling of red blood cells that occur spontaneously and very frequently by the time of microscopic examination.