Adult Parasite:

The adult worm may reach 30 X 13 mm. It is leaf shape with a cone-shaped projection at the anterior end. Living specimens are a grayish-brown in color.

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Hosts: Infects swine, sheep, goats, cattle and other ruminants, horses, humans and other mammals that eat the vegetation on which the metacercaria encysts.

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Life Cycle: The eggs leave the host in the feces and if the egg gets into fresh water the embryo will develop into a miracidium. It takes 2 to 4 weeks for the miracidium to develop after which the operculum of the egg is pushed off and the miracidium uses its cilia to swim out of the egg. The miracidium finds a snail (Lymnaea truncatula) and bores into it. (If the miracidium fails to find a snail within 24 hours, it runs out of energy and dies.) In the snail, the trematode takes up residence in the digestive gland and develops into a sporocyst. Germinal cells within the sporocyst develop into rediae, which when fully developed burst out of the sporocyst. Each redia has a mouth and digestive system and will feed on the snail's tissue. Within the redia germinal cells will develop into a second generation of rediae (daughter rediae). The germinal cells within the daughter redia will develop into cercariae. The time from sporocyst to cercaria is about 1 to 2 months depending on the temperature. The cercaria will burrow out of the snail, swim around until it finds a plant and then will climb a short distance out of the water and encyst on the plant as a metacercaria. When the plant and metacercaria is eaten by a mammal, the larval trematode will emerge from the metacercarial cyst and burrow through the intestinal wall and migrate to the liver which it will also burrow into. After a few weeks of migrating through the liver parenchyma (growing all the time) the young fluke will penetrate into a bile duct where it will mature to the adult stage. Adult liver flukes will feed on the epithelium of the bile duct. Eggs are laid in the bile duct and carried out into the intestine by the bile. The complete life cycle may be completed in 3 to 5 months, the pre-patent period is 10 to 12 weeks.

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Site in host where adult parasite is found:

Bile ducts and occasionally the gall bladder.

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Diagnostic Stage:

Egg:

Measures 130 - 150 by 63 - 90 µm

They have an operculum at one end.

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Common Diagnostic Test

Fecal flotation May distort the egg.
Sedimentation Recovers eggs undistorted.

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Clinical Signs:

Acute disease in sheep (due to a large initial infection) appears while the young fluke are migrating through the liver. The bleeding into the damaged liver may result in weakness, pale mucus membranes, and enlarged livers. Chronic disease results in anemia and hypoalbuminaemia as blood is lost into the bile ducts. The sheep show a loss of condition and sometimes edema.

In cattle the chronic form of the disease is more common and there is the added feature of calcification of the bile ducts over time.
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Treatment:

Albendazole Sheep: 7.5 milligrams per kilogram of body weight (3.4 milligrams per pound). Administer as a single oral dose using dosing gun or dosing syringe.
Cattle: 4.54 milligrams per pound of body weight (10 milligrams per kilogram). Administer as a single oral dose using dosing gun or dosing syringe.

Withdrawal times: Cattle: 27 days before slaughter, Sheep: 7 days before slaughter.

Clorsulon Cattle: 7 milligrams per kilogram or 3.2 milligrams per pound of body weight.

Withdrawal time: 8 days before slaughter.

More information on the use of these products can be found by searching the "FDA Approved Animal Drug Products Online Database System" : http://www.accessdata.fda.gov/scripts/AnimalDrugsAtFDA/

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Comments or Questions please contact: Dr. Nolan at: