Page 155 - The Veterinary Laboratory and Field Manual 3rd Edition

124 Susan C. Cork and Mani Lejeune

Place the plastic Petri dish on top and avoid lidded jars, plenty of water, a clean knife and
trapping air bubbles between. some string will be required.
7 In one go, carefully invert the beaker and add
12 ml of lukewarm water to the Petri dish and 1 Open the abdomen as for a routine post-mor-
leave the setting under light for 4 h allow- tem (see Chapter 8). Tie off the rectum and
ing larvae (L3) to swim from the edge of the oesophagus, in two places, at each end using
beaker into the clean water in Petri dish. string and cut between the tied portions to
8 Collect the content from petri dish and exam- release the entire gastrointestinal tract. Tie
ine under microscope for L3. Identified L3 off and remove the colon, caecum, abomasum
can be saved further for molecular testing. and small intestine (ileum, jejunum). These
components should be placed in separate
dissecting trays (see Figures 3.8–3.10 for the
other helminthological techniques anatomical structures of the ruminant gut).
2 For each portion of the intestinal tract open
Post-mortem (necropsy) up the tract wall to examine the mucosal

Standard helminthological techniques allow an surface and look for the presence of parasitic
estimate of parasite burdens in livestock but worms and/or lesions suggestive of parasite
cannot accurately represent the parasite burden activity, that is, evidence of haemorrhage,
in each and every animal sampled. Some para- thickening or sloughing. Record any unusual
sites may produce few eggs or produce them findings. If coccidiosis or other protozoal
only intermittently, as a result not all infections infections are suspected take mucosal scrap-
will be identified during routine faecal screen- ings from the intestinal wall for examination
ing. In addition, the animal may develop clinical under the microscope.
signs of disease during larval migration before 3 Wash the contents of each portion of the intes-
adult worms reach maturity and produce eggs tinal tract into a 10 l bucket flushing the gut
(that is, patency). In some of these situations lining with clean water (about 5 l). Mix the
the extent of parasite infestation may only be contents of the bucket and remove 100 ml
appreciated at necropsy. The total worm count is from each sample, this should be placed in a
a laborious procedure but can provide valuable lidded jar. Take a small amount of the contents
information, especially in field trials, to assess from each jar and examine under a dissecting
the efficacy (effectiveness) of new anti-parasitic microscope (10× magnification) in a ruled
drugs (anthelmintics) or in cases where anthel- Petri dish (Figure 3.11). If a microscope is not
mintic resistance is suspected. available stain the larvae and adult worms with
iodine solution (2–3 min) and decolourize with
sodium sulphate (30%). The adult worms can
Total worm count
be seen by the naked eye and can be counted.
nEcroPSy (PoSt-MortEM) WorM
countInG tEcHnIquES Calculation: Number of worms counted
This procedure is performed at post-mortem in (note also the number of each species
cases where an estimate of the total parasite load identified) × 100 = total number of
of an animal is required. The following proce- worms present.
dure is recommended for sheep and cattle but
can also be modified for pigs, horses and other 4 Sieving could be done to remove particulates
livestock. Several clean 10 l buckets and 200 ml that hinder examination. This is achieved

Vet Lab.indb 124 26/03/2019 10:25