DIFFERENTIAL DIAGNOSIS OF MALARIAL PARASITES 
59 
II. DIFFERENTIAL DIAGNOSIS 
Schizogonous Cycle 
General Appearance of Thin and 
Thick Blood Films 
The blood picture presented by the thin 
film fixed with methyl alcohol and stained 
by one of the stains mentioned is too famil¬ 
iar. to warrant discussion. The descriptions 
of the morphology of malarial parasites are 
based on their appearance in films of this 
type. They lie within or on the erythro¬ 
cytes, show red to purplish-red chromatin, 
blue cytoplasm, and pigment granules vary¬ 
ing from a yellow tinge to almost black. 
Differentiation by stages and species in the 
thin film is given in the accompanying 
Table II. Further detail may be found in 
James, Nicol and Shute (1933); Nocht and 
Mayer (1937); Stitt, Clough and Clough 
(1938) ; Thompson and Woodcock (1922), 
and Wenyon (1926b). A working knowl¬ 
edge of the morphology of the malarial 
parasites in the thin film is absolutely 
necessary before attempting their diagnosis 
in the thick film. 
TABLE II 
Summary of Parasite Differentiation 
(Stained thin films) 
P. 
vivax 
P. 
falci¬ 
parum 
P. 
ma¬ 
lariae 
P. 
ovale 
Infected cell . 
(a) 
(b) 
(c) 
(d) 
Small tropho¬ 
zoite (early 
rings) . 
(a) 
(b) 
(c) 
(d) 
Growing 
trophozoite . 
(a) 
(b) 
(c) 
(d) 
Large 
trophozoite . 
(a) 
(b) 
(c) 
(d) 
Presegmenting 
schizont . 
(a) 
. ( b ) 
(c) 
(d) 
Segmenting 
schizont . 
(a) 
(b) 
(c) 
(d) 
Macro- 
gametocyte . 
(a) 
(b) 
(c) 
(d) 
Micro- 
gametoeyte . 
(a) 
(b) 
(c) 
(d) 
Length of asex¬ 
ual cycle . 
48 hrs 
48 hrs 
72 hrs 
48 hrs 
Stages in 
peripheral 
blood . 
All 
(b) 
All 
All 
Remarks . 
(a) 
(b) 
(c) 
(d) 
Note. The above table is a guide to differenti¬ 
ating the species of Plasmodia. The first column 
lists the chief stages of the parasites as found in 
thin smears. It is from differences in the charac¬ 
teristics of these stages that the species may be 
determined. In the text below the stages appear at 
the beginning of paragraphs in the same order as 
in the table above. In each paragraph the four 
species are given in the same order and following 
the same letters as in the table. To read down 
through a paragraph below is equivalent to reading 
across the corresponding line in the table above. 
Infected cell, (a) Larger than normal, pale, 
often bizarre in shape. Schiiffner ’s dots very often 
present. Multiple infection of erythrocyte not un¬ 
common. (b) Normal in size. Multiple infection 
of erythrocytes more frequent than in the other 
species.- Maurer’s dots sometimes seen (in over¬ 
stained smears or when pH of H 2 0 is on alkaline 
side). (c) About normal or slightly smaller. 
Sometimes darker in early stages. Ziemann’s dots 
rarely seen. Multiple infection of erythrocyte rare, 
(d) Somewhat larger than normal, often with 
fringed or irregular edge and oval in shape. 
Schiiffner’s dots appear even with younger stages, 
stain more readily and more deeply than in vivax. 
Small trophozoite (early rings). (a) Signet ring 
form with heavy chromatin dot and large cyto¬ 
plasmic circle, possibly with fine pseudopodia, (b) 
Small threadlike cytoplasmic circle, and one or two 
small chromatin dots. (Double chromatin dots 
more frequent than in other species.) Marginal 
and bridge forms are frequent. May disappear in 
this stage from peripheral circulation and return 
to internal organs for development, (c) Signet 
ring form with heavy chromatin dot and cyto¬ 
plasmic circle which is often smaller, thicker, and 
heavier than that of vivax. (d) Small, darker in 
color and more solid, as a rule, than those of falci¬ 
parum. Schiiffner’s dots regularly present in 
almost 100% of infected cells. 
Growing trophozoite, (a) Same as above with 
gradual increase in amount of cytoplasm and chro¬ 
matin. Often with more distinct pseudopodial 
processes. Small yellowish-brown pigment granules 
in cytoplasm, number increasing with age of para¬ 
site. (b) This stage remains in the ring form but 
chromatin and cytoplasm increase to the extent that 
in size the parasite resembles closely the small 
trophozoite of vivax. A few pigment granules give 
a yellowish tinge to the cytoplasm. This is usually 
the oldest asexual stage seen in peripheral circula¬ 
tion. (c) Chromatin rounded or elongated, cyto¬ 
plasm in a compact form with little or no vacuole 
or in a narrow band form across the cell. Dark 
brown pigment granules—may have peripheral ar¬ 
rangement. (d) Resembles closely same stage of 
P. malariae, but is considerably larger. Pigment is 
lighter in color and less conspicuous. 
Large trophozoite, (a) One abundant mass of 
chromatin, loose, irregular or close compact cyto¬ 
plasm, with increasing amounts of fine brown pig¬ 
ment. Parasite practically fills enlarged cell by end 
