Part B: Classification of Parasitic Organisms - helminths
Examine the parasites contained in the glass vials. Based on your observations identify them from the following descriptions.
Vial 1
Vial 2
Vial 3
Vial 4
Vial 5
Helminths (Phylum nemathelminths and Phylum platyhelminths)
Parasitic worms. Does not include earthworms and leeches.
Class Trematoda
Flattened worms. Not segmented (one piece).
| Fasciola hepatica (liver fluke) |
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May be up to 30 by 13 mm. Leaf shaped. Broader anteriorly than posteriorly, with a cone shaped projection that is followed by a pair of broad “shoulders”. It is greyish brown in colour. Found in the bile ducts of ruminants. Causes irritation of the bile duct and damage to the liver in the developmental stages. The liver damage can lead to the fatal Clostridial disease, Black Disease.
Class Cestoda
Elongated flattened. Segmented sections are continuously produced and separate from the rest of the worm.
| Monensia expansa (sheep tapeworm) |
|
May reach the length of 600cm and a width of 1.6 cm. The segments are much broader than long.
Found in the small intestine of sheep, usually only 6 months or less. Small light infections are considered of little importance.
Class Nematoda
Roundworms (cylindrical). Both ends are somewhat pointed. The cuticle (skin) is smooth and looks slightly shiny when wet. Not segmented. They have an anterior mouth that may be large or small that allows them to feed. The anterior end has an opening for waste and the expulsion of eggs. The tail is typically sharper than the head, except that the males have broad flipper-like extensions called bursae.
| Chabertia ovina (large-mouthed bowel worm) |
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The females are 17 to 20 mm long. The anterior end is curved slightly and has a large bowl-shaped mouth opening.
Occurs in the colon of sheep, goats and cattle. By attaching with the large mouth they then digest the lining of the colon. This causes inflammation of the large intestines and sheep may become anaemic and die but it is unlikely to occur unless in large numbers.
| Haemonchus contortus (barbers pole worm) |
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Males are 10 – 20 mm and females are 18 – 30 mm long. In the fresh specimen the females their red intestinal tract coils around the white reproductive tract as it descends through the body. In preserved specimens the intestine appears as to spiral down through the lighter outer parts of the body. It has a relatively small mouth region. The males have flipper like projections on their tails for holding on to the females.
This is the most pathogenic worm of sheep. Occurs in the abomasum of the sheep, but also goats and cattle. In weaners there can be large numbers. The worms suck large volumes of blood making the sheep weak and anaemic. It can kill large numbers if the weaners are under nutritional stress.
| Tricuris ovis (whip worm) |
|
The anterior three-quarters is slender than the thicker posterior section. The whole worm may be 35 – 80 mm long. It is found in the caecum of goats, sheep and cattle. It rarely causes sufficient irritation or damage to cause serious harm but it may cause scouring that may lead to soiled breech areas and then fly-strike.
