Examination of blood for parasites Medical Parasitology
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Parasites found in blood 1. Microfilaria. 2. Malaria. 3.
Babesia. 4. Lieshmania. 5. Trypanosomes. 6. Toxoplasma.
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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.
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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.
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BLOOD FILMS WITH GEIMSA Thin Thick Blood drop spread Air dry
Fix by methyl alcohol 10-30 sec Geimsa stain Wash & dry Air dry
Circular motion Dehaemoglobinzed Geimsa stain 45 min Wash &
dry
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BLOOD FILMS WITH LIESHMANs Thin Thick Blood drop spread Air dry
Fix and stain 1 min Transfere into 1 stain: 3 distilled water. Wash
and dry Air dry Follow the same as in thin film Circular motion
Dehaemoglobinzed 3 Blood drops
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Fixation with methanol. This step is not needed in Lieshmans
stain as it contains methanol. Staining by immersion in the
staining dishes Washing of the thin filmCareful washing of the
thick film
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Normal peripheral blood smear Normal peripheral blood
smear
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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. Mainly with intracorpuscular
parasites as Malaria and Babesia for morphological description in
relation to RBCs. Thin blood filmsThick blood films
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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 Knotts conc technique.
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KNOTTS CONC. TECHNIQUE 10 ml 1 ml Air dry Geimsa Citrated blood
Citrated blood Formalin 2 % sediment 2 min centrifuge
Microfilaria
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Thick blood film showing microfilaria of W. bancrofti Thick
blood film showing microfilaria of B. malayi
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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.
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P. vivax Ring-forms Thin blood filmThick blood film
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P. vivax -Schizonts Thin blood film Thick blood film
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P. vivax -Macrogametocytes Thin blood film Thick blood
film
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P. falciparum -Ring-forms Thick blood film Thin blood film
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P. falciparum -Gametocytes Thin blood film Thick blood
film
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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. divergensB. microti
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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.
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Trypansoma brucei ssp. in thick blood film Trypansoma brucei
ssp. in thin blood film
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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 Chagas disease is transmitted by the bite
of Rudvid bug.
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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
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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
is transmitted by the bite of Sand fly. Leishmania spp.
amastigotes
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Buffy coat film centrifuge RBC WBC (BC) plasma Citrated blood
30 min Air dry Fix spread Geimsa Tryp., L. donovani
Slide 27
Toxoplasma Thin and thick blood stained smears for
visualization of parasites in cases of acute toxoplasmosis.
Tachyzoite stage in thick blood film
