1. Malaria Blood Smear Remains the gold standard for diagnosis
Giemsa stain
distinguishes between species and life cycle stages
parasitemia is quantifiable
Threshold of detection
thin film: 100 parasites/l
thick film: parasites/l
Requirements: equipment, training, reagents, supervision
Simple, inexpensive yet labor-intensive
Accuracy depends on laboratorian skill

2. Interpreting Thick and Thin Films
THICK FILM
lysed RBCs
larger volume
0.25 μl blood/100 fields
blood elements more concentrated
good screening test
positive or negative
parasite density
more difficult to diagnose species
THIN FILM
fixed RBCs, single layer
smaller volume
0.005 μl blood/100 fields
good species differentiation
requires more time to read
low density infections can be missed

3. Malaria Blood Smear
Prepare smears as soon as possible after collecting venous blood to avoid
Changes in parasite morphology
Staining characteristics
Take care to avoid fixing the thick smear
Risk of fixing thick when thin is fixed with methanol if both smears on same slide
Let alcohol on finger dry to avoid fixing thick
Be careful if drying with heat

4. Collection of Blood Smears1.
The second or third finger is usually selected and cleaned. 4.
Slide must always be grasped by its edges. 5.
Touch the drop of blood to the slide from below. 2.
Puncture at the side of the ball of the finger. 3.
Gently squeeze toward the puncture site.

5. Preparing thick and thin films4.
Carry the drop of blood to the first slide and hold at 45degree angle. 1.
Touch one drop of blood to a clean slide. 2.
Spread the first drop to make a 1 cm circle. 5.
Pull the drop of blood across the first slide in one motion. 3.
Touch a fresh drop of blood to the edge of another slide. 6.
Wait for both to dry before fixing and staining.

6. Recognizing Malaria Parasites
Blue cytoplasm
Inside a red blood cell
One or more red chromatin dots

7. Recognizing Erythrocytic Stages: Schematic Morphology
RING
TROPHOZOITE
SCHIZONT
GAMETOCYTE
Blue
Cytoplasm
Red
Chromatin
Brown
Pigment

8. Malaria Parasite Erythrocytic Stages
Ring form
Trophozoite
Schizont
Gametocytes

9. Plasmodium falciparum
Infected erythrocytes: normal size M I
Gametocytes: mature (M)and
immature (I) forms (I is rarely
seen in peripheral blood)
Rings: double chromatin dots; appliqué forms;
multiple infections in same red cell
Schizonts: 8-24 merozoites
(rarely seen in peripheral blood)
Trophozoites: compact
(rarely seen in
peripheral blood)

10. Plasmodium vivax
Infected erythrocytes: enlarged up to 2X; deformed; (Schüffner’s dots)
Rings
Trophozoites: ameboid; deforms the erythrocyte
Schizonts: merozoites
Gametocytes: round-oval

11. “malariae - like parasite in vivax - like erythrocyte”
Plasmodium ovale
Infected erythrocytes: moderately enlarged (11/4 X); fimbriated; oval; (Schüffner’s dots)
“malariae - like parasite in vivax - like erythrocyte”
Trophozoites: compact
Rings
Gametocytes: round-oval
Schizonts: 6-14 merozoites;
dark pigment; (“rosettes”)

12. Plasmodium malariae
Infected erythrocytes: size normal to decreased (3/4X)
Trophozoite:
typical
band form
Trophozoite:
compact
Schizont:
6-12 merozoites;
coarse, dark pigment
Gametocyte:
round; coarse,
dark pigment

13. Species Differentiation on Thin Films

14. Species Differentiation on Thin Films

15. Species Differentiation on Thick Films