Page 581 - The Veterinary Laboratory and Field Manual 3rd Edition

518 Samuel Sharpe

submitted for testing. Warning labels which toxicology
meet requirements in your area should be affixed
to sample containers to notify that sample con- Toxicological testing will be performed on fresh
tains potentially bio-hazardous materials. tissue. Samples taken for this purpose should not
be fixed in formalin. Samples can be taken into
leak proof containers and shipped to the labora-
Cross contamination
tory on ice packs. If a delay in testing is expected,
Infectious agents will be detected by either grow- samples can be frozen at –20ºC. Appropriate
ing the agent in vitro (that is, bacterial or fungal tissues will depend on the toxin of interest and
culture or virus isolation in cell culture) or by on the specific requirements of the toxicology
a molecular test (for example, PCR, ELISA and laboratory. In general, it should be noted that
so on). In either case false positives can occur if investigation of possible intoxication should try
contamination of the sample occurs. to establish ingestion, metabolism, and excre-
To minimize the chance of contamination, tion of the toxin in question.
ensure the following. Note that toxicological assessment requires
a large volume of sample therefore at least 10 g
• Use fresh instruments (that is, blades, for- of tissue or another sample should be retained
ceps, scissors and so on) when collecting if possible.
samples.
• Package each sample in a separate con-
tainer. Do not submit all samples together Ingestion
in the same container as contamination will Careful gross examination of stomach contents
occur. may identify the presence of toxic material (for
• Take samples of other organs prior to opening example, bait containing a poison, metallic object,
the GI tract. or suspect plant material). If not, a sample of
stomach contents should be taken and kept fro-
zen prior to submission for toxicological analysis.
Parasitology
Metabolism
Faecal egg count: Estimation of parasite burden
can be provided by submitting a fresh faecal Many drugs and toxins are metabolized in
sample for a faecal egg count. Fresh faeces (5 g) the liver and a liver sample should always be
should be collected into a clean plastic or glass retained in these cases.
container and refrigerated prior to submission Fat soluble agents will be concentrated in
to the laboratory. Do not freeze: as this may tissues with high lipid content: for this reason,
damage eggs within the sample and produce an adipose tissue and brain should be retained
artefactually low count. (see section on sampling the brain). Testing for
If more detailed investigation of the number organophosphates (OPs) is performed by mea-
and types of parasites present is required, all gut suring the activity of acetylcholinesterase in the
contents should be collected according to loca- brain. OPs inhibit acetylcholinesterases and OP
tion in the GI tract and submitted for total worm intoxication is indicated by reduced acetylcho-
count. linesterase activity.
Aqueous humour in the anterior chamber
of the eye is a dialysate of blood plasma and

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