Page 69 - The Veterinary Laboratory and Field Manual 3rd Edition

38 Susan C. Cork, Roy Halliwell and Willy Schauwers

collection of material for laboratory to be sampled, contamination can be mini-
examination mized by swabbing the outside of the bone
with disinfectant, splitting the bone open
The quality of diagnostic service offered by the and then aseptic extraction of the marrow by
laboratory is determined, to a large extent, by using a sterile swab.
the quality and suitability of the specimens or 2 Never freeze samples for bacteriology.
samples that are submitted and the information 3 Samples for bacteriology should preferably
on the case(s) that is provided. The laboratory be: delivered to the laboratory in a cool box/
cannot be expected to assist with making an chiller within 8 h in summer and within 12 h
accurate diagnosis without relevant information in winter (although this will depend on the
and properly selected and submitted samples. It local climatic conditions).
is the responsibility of the veterinarian, if pres- 4 Try to keep the various tissues separated from
ent, to select specimens but in his/her absence, one another. If tissue samples are grouped
especially in rural areas, it is often the livestock together, bacteria from one sample can con-
or animal health extension worker who has to be taminate another. This is especially true if
aware of the criteria used to select good samples. intestinal samples or faeces are included.
5 Samples should be kept moist. If the sample
dries out, any pathogens present might die,
Sampling and laboratory diagnosis
therefore culture will not be possible.
To test or not to test? This is the first question 6 For histopathology, 10% buffered formalin
to ask. Is a laboratory test desirable, necessary preservative should be added to the tissue
or possible? A number of factors, including fea- (add as a 10 : 1 proportion of formalin to tis-
sibility and cost need to be considered. However, sue volume).
once the decision is made to collect samples it is
important to ensure that they reach the labora- B: Key concepts for handling and preserving
tory in a timely manner and in good condition. other samples
Some general guidelines on how to collect, pre-
serve and submit samples are provided below. 1 For swabs, immerse the swab in transport
media and keep at 4°C until it can be sent to
GEnEraL ruLES on HoW to bESt PrESErvE the laboratory. Different transport media are
SaMPLES For SubMISSIon to tHE required for specific pathogens.
Laboratory 2 For blood samples, keep the EDTA tube at
A: Some key concepts to keep in mind for tissue 4°C and mix the tube gently after sampling.
samples include: If the EDTA blood cannot be examined the
same day, a thin blood smear should be
1 Keep the tissues cool (for example, in a cool prepared and fixed directly after taking the
box at 4°C). Bacterial contaminants will be blood. This can then be stained for examina-
present in ANY sample unless they have tion at the laboratory.
been collected aseptically. Unfortunately, the 3 For serum samples, let the blood sit in a
contaminants often replicate faster than the holding rack until it has coagulated. This
disease-causing bacteria of interest. Keeping is best done by collecting the sample in a
the samples chilled will slow down bacterial plain vacutainer (that is, red topped without
growth and enhance the chances of culturing anticoagulant) and leaving for 12–24 h (in
the pathogen. If marrow from a long bone is summertime the samples can often be left on

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