Page 203 - The Veterinary Laboratory and Field Manual 3rd Edition

172 Susan C. Cork and Mani Lejeune

carry low numbers of haemoprotozoa or some parts of the world. It is also possible to
Anaplasma sp. without apparent clinical disease. select animals that are genetically more resis-
tant to the vectors which spread the diseases
and therefore have a reduced challenge. Details
diagnosis, control and prevention about the treatment, prevention and control of
specific haemoparasites are provided later in this
Diagnosis of haemoparasitic disease is usually section and more information is available in the
made on clinical and epidemiological grounds bibliography at the end of the chapter.
with confirmation of the cause obtained through
collection and examination of stained blood
smears. The appearance of the parasites in blood Preparation and examination of blood
smears is usually characteristic allowing ready and tissue smears for the presence of
identification, although in some cases an animal haemoparasites
may be infected with more than one organism at
the same time. In cattle and sheep, smears can The preparation of a good blood film requires the
easily be made from blood collected from the ear use of clean grease free slides (storage of slides in
vein but smears can also be made from whole 70% alcohol will remove grease but allow these
blood collected in EDTA for concurrent hae- to dry before use). The film should be made from
matology tests. However, peripheral (capillary) a single drop of peripheral blood, for example,
blood is more likely to contain haemoparasites from the ear vein. Peripheral (capillary) blood
than blood from the central veins. In many cases is more likely to contain haemoparasites than
the number of haemoparasites in the circulation blood from the major veins but smears can also
may be low so it is a good idea to prepare thick be prepared from an EDTA sample submitted in
smears as well as thin smears of peripheral blood. a vacutainer if a capillary sample is unavailable.
Where possible, ensure that all glass slides are The prepared film should be smooth and even,
labelled using a glass marker because most nor- allowing random distribution of white cells
mal marker pens will be washed off when the throughout the film; the erythrocytes should
smears are fixed. In addition to the examination be distributed in a single layer (see Chapter
of blood smears there are molecular and anti- 5). A spreader can be used for preparation of
gen detection assays and a range of serological smears, this should have smooth even edges
screening tests (predominantly ELISA based) to with the corners cut to give a side 1.5 cm wide
detect the presence of, or exposure to, a range (slightly narrower than the microscope slide).
of haemoparasites. These will not be considered For examination of some haemoparasites it is a
further here but are well described in a number good idea to prepare thin smears as well as thick
of texts listed at the end of this chapter. smears, the latter especially where the number
The prevention and control of haemopara- of parasites is low. The following techniques (see
sitic disease requires an understanding of the Figure 3.36) may be used to make thin and thick
life cycle of the parasite and that of the vector. A smears.
successful control programme will require con-
current ectoparasite control (see Section 3.7). Methods
There has been significant research into the
development of preventative vaccines to reduce PrEParatIon oF a tHIn FILM
the impact of haemoparasitic disease in rumi- Place a small drop of blood 1.5–2 cm from one
nant species and these seem to be effective in end of a clean slide. Hold the spreader at an

Vet Lab.indb 172 26/03/2019 10:25