Page 204 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 173

Figure 3.36 Preparation of a blood
film (see also Figures 5.2a and b,
5.6 and 5.7.

angle of 30° in front of the drop of blood and it at an angle in distilled water (2 min). Fix the
bring back to touch the blood allowing it to slide in methanol. In the laboratory, the slides
spread along the edge. Make the film by pushing can be stained with Giemsa or Leishman stain.
the spreader forward in a direct and even move- There are a number of smear preparation
ment. The film should be about 3–4 cm long. (apart from the two mentioned above) and stain-
Air dry rapidly by waving the film in the air (this ing methods recommended but the following
avoids crenation of the erythrocytes). Label the have also been found satisfactory in our experi-
film, either by writing with a pencil in the film ence.
itself or, if in the laboratory, etch the slide using
a diamond tipped pen. Fix the film in methanol Smear preparation
for 2 min as soon as the blood film is completely
dry (the film will not fix to the slide if it’s wet dIrEct ExaMInatIon oF a FrESH WHoLE
at the time methanol is added). If fixing is bLood
delayed the film can deteriorate rapidly therefore For some blood parasites, especially that live
it is advisable to carry a small bottle of methanol outside of blood cells, such as Trypanosoma sp.
for this purpose when out doing fieldwork. and microfilaria of helminths, it is a good idea
to initially examine fresh whole blood. This can
PrEParatIon oF a tHIck FILM be done by placing a drop of blood on a slide
Place a drop of blood at one end of the slide. and examining under a microscope with or
Touch the drop of blood with a spreader and without a cover slip on top of blood. The organ-
make a thin film starting at 3 cm from the end isms can be appreciated based on their motion,
of the slide (Figure 3.36). Spread the remain- if they are still viable and motile. A parasite-
ing blood in the shape of a cube (3 × 20 mm). free blood film appears standstill. However,
If the film is too thick it will peel off the slide. the corkscrew motion of trypanosomes cause
Air dry completely and draw a line between the tumbling movement of adjacent red blood cells.
two films. Haemoglobin can be removed from Similarly, snakelike motion of some microfilariae
the thick film by inverting the slide and placing is reflected by a wavy movement of red blood

Vet Lab.indb 173 26/03/2019 10:25