Page 157 - The Veterinary Laboratory and Field Manual 3rd Edition

126 Susan C. Cork and Mani Lejeune

Figure 3.11 Relative size of adult worms which may be seen during a total worm count at post mortem
examination. (A) Calibrated petri dish, (B) view under dissecting microscope.

by running the aliquots through a sieve 5 Encysted larvae (L4) on the mucosa of
of 400 µm mesh. The sieve size is selected abomasum can be recovered by either digest-
based on the helminths that is expected in ing the whole or a portion of the organ.
the sample. For example, a 37.5 µm mesh is 6 For complete morphological examination
preferred for abomasal specimen (for L4 of helminth specimens should be appropri-
Haemonchus and Ostertagia); whereas, a larger ately preserved. Live nematodes collected
sieve is required for large intestinal specimen at necropsy should be dropped into warm
(for adult Trichuris). Descriptions and mea- 70% ethanol so they stretch and present a
surements of the more common intestinal wrinkle free cuticle to aid morphological
helminths are given in Table 3.1. identification. Similarly, live cestodes/trema-

Table 3.1 Approximate size and location of common helminth parasites.

Location Size Gross characteristics
Abomasum
Haemonchus sp. 2 cm long Females are red when fresh (Barber’s pole appearance)
Ostertagia sp. 1 cm long, slender Brown when fresh
Trichostrongylus axei < 0.5 cm long Grey when fresh, not readily seen on the abomasal wall
Small intestine
Bunostomum sp. 2 cm long Stout white worms with a bent head
Nematodirus sp. 2 cm long Slender worms, often twisted in clumps
Trichostrongylus sp. 0.5 cm long Grey slender worms
Strongyloides sp. 0.5 cm long Grey slender worms
Cooperia sp. 0.5 cm long Grey and comma shaped
Large intestine
Chabertia sp. 1.5–2.0 cm long Large bell-shaped mouth
Oesophagostomum sp. < 2 cm long Head bent, tapered buccal capsule
Trichuris sp. < 8 cm long Whip like, long filamentous anterior part longer than
posterior part

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