Some characteristic features of the malarial parasites of humans (Romanowsky-stained preparations and others)

1. Some characteristic features of the malarial parasites of humans (Romanowsky-stained preparations and others)
Plasmodium vivax Plasmodium malariae Plasmodium falciparum Plasmodium ovale
Parasitized red cells Enlarged; other references
indicate that they prefer
reticulocytes (immature
erythrocytes; Fine stippling
(Schüffner's dots).
Not enlarged. No stippling
(except with special stains).
Ziemann’s dots (granules/
pigments present). Invades all
RBCs regardless of age.
Primarily invades older/
senescent RBCs.
Not enlarged. Coarse stippling
(Maurer’s clefts). Invades all
RBCs regardless of age. Some
references indicate that they
prefer non-enlarged RBCs
Enlarged; other references
state that they prefer
reticulocytes (immature
erythrocytes; Schüffner's dots
conspicuous. Cells fimbriated
or crenated
Ring stage trophozoites Large rings (1/3-1/2 red cell
diameter). Usually one
chromatin granule; ring
delicate
Large rings (1/3 red cell
diameter). Usually one
chromatin granule; ring thick
Small rings (1/5 red cell
diameter). Often two granules,
multiple infections common;
ring delicate, may adhere to
red cells
Large rings (1/3 red cell
diameter). Usually one
chromatin granule; ring thick
Pigment in developing
trophozoites
Fine; light brown; scattered Coarse; dark brown; scattered
clumps; abundant
Coarse; black; few clumps Coarse; dark yellow-brown;
scattered
Older trophozoites Very pleomorphic Occasional band forms Compact and rounded Compact and rounded
Mature schizonts More than 12 merozoites (14-
24)
Fewer than 12 large
merozoites (6-12). Often in
rosette.
Usually more than 12
merozoites (8-32). Very rare
in peripheral blood
Fewer than 12 large
merozoites (6-12). Often in
rosette.
Gametocytes Round or oval. Round or oval. Crescentic/ banana-shaped Round or oval.
Distribution in peripheral
blood
All forms All forms Only rings and crescents
(Gametocytes)
All forms
Incubation period (days) 8-22 (14) 15-30 8-25 (12 on average) 9-17 (15)
Duration of untreated
infection (years)
1.5-4 1-30 0.5-2 Probably 1.5-4
Developmental period in
mosquito vector
10-16 days at 20-25 degrees
centigrade
25-35 days at 20-24 degrees
centigrade
10-23 days at 20-27 degrees
centigrade
14-16 days at 25-27 degrees
centigrade