Medical Parasitology
Examination of blood for
parasites
Parasites found in blood
1. Microfilaria.
2. Malaria.
3. Babesia.
4. Lieshmania.
5. Trypanosomes.
6. Toxoplasma.
Preparation of blood films
Thin blood film
1. Place a small drop of blood near one end of a clean slide.
2. Spread by another slide held at an angle, so that the
blood drop will run along the back of the spreader edge.
3. The spreader slide is then pushed forward to the other
end of the slide spreading a thin film of blood.
4. Air dry.
5. Fixation by methyl alcohol.
6. Stain in staining dishes.
7. Wash with distilled water, air dry and examine.
Thick blood film
1. Place 4 drops of blood close together on the centre
of a slide.
2. Pool the drops together with the corner of another
slide making a square of 1x1 cm.
3. Dehaemoglobinize by immersion in distilled water
until Hb dissolves and the film become
transulescent.
4. Air dry.
5. Stain in staining dishes.
6. Wash with distilled water, air dry and examine.
BLOOD FILMS WITH GEIMSA
 Thin
Thick
Blood drop
spread
Air dry
Fix by methyl
alcohol
10-30 sec
•Geimsa stain 45
min
•Wash & dry
Circular motion
Air dry
Dehaemoglobinzed
•Geimsa stain
•Wash & dry
BLOOD FILMS WITH LIESHMAN’s
 Thin
Thick
3 Blood drops
Blood drop
spread
Air dry
Fix and stain
1 min
•Transfere into 1 stain: 3 distilled
water.
•Wash and dry
Circular motion
Air dry
Dehaemoglobinzed
Follow the same
as in thin film
Fixation with methanol.
This step is not needed in
Lieshman’s stain as it
contains methanol.
Staining by immersion in the staining
dishes
Washing of the thin film
Careful washing of the thick film
Normal peripheral blood smear
Thin blood films
 Mainly with
intracorpuscular parasites
as Malaria and Babesia
for morphological
description in relation to
RBCs.
Thick blood films
 Thick films allow to screen
a larger volume of blood
and is better with scanty
infections.
 Mainly with sheathed
microfilaria as the sheath
is the characteristic for type
of parasite may be
disturbed by spreading the
thin films.
Microfilaria
 The larval stage of the filarial worms.
 It is found in blood in cases of W. bancrofti and B. malayi -
the causative organisms of lymphatic filariasis- showing
periodicity.
 Lymphatic filariasis is a disease transmitted by bite of
female mosquitoes of genus Culex, Aedes and Anopheles.
 Thick blood film is preferred for examining a blood film
for microfilaria.
 Concentration techniques can be used prior to
microscopic examination “Knott’s conc technique”.
KNOTT’S CONC. TECHNIQUE
Citrated
blood
1 ml
centrifuge
10 ml
Air dry
2 min
Formalin 2 %
Geimsa
sediment
Microfilaria
Thick blood film showing
microfilaria of W. bancrofti
Thick blood film showing
microfilaria of B. malayi
Malaria
 Four species are considered true parasites of humans, as they utilize humans
almost exclusively as a natural intermediate host: P. falciparum, P. vivax, P.
ovale and P. malariae.
 It is transmitted through bite of female Anopheles mosquitoes.
 Microscopic identification by examining thick and thin blood films is the
method most frequently used to demonstrate an active infection.
 In P. vivax, P. ovale and P. malariae ring, trophoziote, schizont,
gametocyte stages can be seen in a blood film.
 In cases of P. falciparum only ring and gametocyte stages are seen
because of the adhesion phenomena.
P. vivax Ring-forms
Thick blood film
Thin blood film
P. vivax -Schizonts
Thick blood film
Thin blood film
P. vivax -Macrogametocytes
Thick blood film
Thin blood film
P. falciparum -Ring-forms
Thick blood film
Thin blood film
P. falciparum -Gametocytes
Thick blood film
Thin blood film
Babesia
 It is a zoonatic disease transmitted to human by tick bite.
 Microscopic identification by examining thick and thin
blood films is the method most frequently used to
demonstrate an active infection.
B. microti
B. divergens
Trypanosomes
Trypanosoma brucei
 A wet blood preparation should be examined for the motile
trypanosomes, and in addition a smear should be fixed, stained and
examined.
 Thin and thick blood stained smears for visualization of parasites.
 Concentration techniques can be used prior to microscopic
examination “Buffy coat film”.
 African trypanosomiasis “sleeping sickness” is transmitted by the
bite of Tsetse fly.
Trypansoma brucei ssp. in thin blood
film
Trypansoma brucei ssp. in thick blood
film
Trypanosoma cruzi
 A wet blood preparation should be examined for the motile
trypanosomes, and in addition a smear should be fixed, stained and
examined.
 Concentration techniques can be used prior to microscopic
examination “Buffy coat film”.
 Thin and thick blood smears stained with Giemsa, for
visualization of parasites.
 American trypanosomiasis “Chaga’s disease” is transmitted by
the bite of Rudvid bug.
T. cruzi trypomastigotes in a thick
blood smear stained with Giemsa
T. cruzi trypomastigotes in thin blood
smears stained with Giemsa
Note the typical C-shape of the trypomastigote that
characterizes T. cruzi in fixed blood smears
Lieshmania
 Concentration techniques can be
used prior to microscopic
examination “Buffy coat film”.
 Thin and thick blood stained
smears stained for visualization of
parasites.
Leishmania spp.
 Leishmania is transmitted by the amastigotes
bite of Sand fly.
Buffy coat film
plasma
centrifuge
30 min
Citrated blood
WBC (BC)
RBC
Air dry
spread
Fix
Geimsa
Tryp., L. donovani
Toxoplasma
 Thin and thick blood stained smears for visualization of
parasites in cases of acute toxoplasmosis.
Tachyzoite stage in thick blood film