Page 223 - The Veterinary Laboratory and Field Manual 3rd Edition

192 Susan C. Cork and Mani Lejeune

Skin scrapings and tissue digestion

Examination procedure
dIrEct MEtHod
Place the sample (skin/hair) on a slide and mix
with a little oil or water. Examine the slide with
the microscope using low power (4×). For large
parasites (ticks, some lice) examination may be
done using a dissecting microscope.

aLkaLI dIGEStIon MEtHod
Digestion methods are used to allow a more
‘clear’ view of parasites taken from skin scrap- Figure 3.46 Dorsal view of two species of adult
ings. Place a portion of the sample in a test tube louse (insects – three pairs of legs). (A) Linognathus
and add 5 ml of 10% KOH (or NaOH). Heat the sp. (sucking louse), (B) Damalinia sp. (biting louse).
sample gently to boiling point (about 5 min) Most species of lice are fairly host specific.
until a homogenous solution remains in the
tube. Do not allow the solution to boil as it will may cause some irritation but this is usually
splash and KOH is corrosive. Allow the sample less severe than that seen in mite infestation.
to cool and then centrifuge for 5 min at low Sucking lice largely infest mammals whereas bit-
speed. The sediment at the bottom of the tube ing lice can be found on mammals and birds.
can then be examined under the microscope Heavy infestations of sucking lice can cause
for mites and fungi. For examination of fungal severe anaemia. Both sucking and biting lice
hyphae, fix the sample in 70% alcohol and stain can cause irritation and self-trauma, which may
with lactophenol cotton blue stain (LPCB) (see lead to secondary bacterial infection and dam-
also Chapter 4, section 4.6). age to the skin/hide. The control and prevention
of louse infections requires an understanding
of the louse life cycle and attention to animal
3.10 Lice and other insects husbandry and environmental conditions.
Lice are known to transmit some bacterial
Lice and rickettsial diseases such as typhus (for
example, Rickettsia typhi). Diagnosis of louse
There are two main suborders of lice, the ano-
plura (sucking lice) and the mallophaga (biting infestation is confirmed by collecting samples of
lice). In general, lice are fairly host specific with hair, this may be done by removing loose hair by
each species of animal having its own range of the roots or by cutting with a scalpel blade at the
lice. In cattle, the most common species include base of the shaft. In this way, adult lice and eggs
the biting louse, Damalinia sp., and the sucking may be collected. Such samples can be placed in
lice, Linognathus sp. and Haematopinus sp. (Figure a labelled and sealed plastic bag and submitted
3.46). Disease caused by lice is known as pedic- for examination under the dissecting microscope
ulosis. Heavy infestations are more common (Figure 3.46).
in housed, over-crowded and debilitated indi-
viduals. Infestations are fairly easy to treat but
re-infection is often a problem unless animals
are moved to a ‘clean’ environment. Pediculosis

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