Plasmodium malariae
Causative agent of quartan fever (fever on the first day, remission of fever
on the second and third, return of fever on the fourth). It is an infection
that follows a benign course except in a few cases. Compared with the other
species, it generally produces very low parasitemia. The infection persists
in humans for a very long time, up to 50 years or more [26], even in the
absence of reinfection. The long duration of the infection may be explained
by the slow rate of erythrocytic schizogony, 72 hours, and by the fact that
the parasite cannot be completely eliminated using the standard doses of
anti-malaria drugs with blood schizonticidal action. Moreover, from a
phylogenetic point of view, it is the species that has been infecting man
for the longest time and has thus adjusted to the human immune system,
which is unable to completely eliminate the parasite. Relapses, which occur
in the absence of reinfection, are actually recrudescences due to subpatent
parasitemia (Plate 10).
Parasitized red blood cells
As a rule, they are old red cells; this explains the low parasitemia [46].
Size: normal or slightly reduced.
Shape: round, unchanged.
Granulations: Ziemann’s stippling, which is not visible with normal stains
and hence of no diagnostic value.
Polyparasitism: highly uncommon.