Redwanullah Memlawal2012-MPhil-1504

Department of Parasitology

Scientific ClassificationKingdom: Animalia

Phylum: PlatyhelminthesClass: Trematoda

Subclass: DigeneaOrder: Echinostomida

Family: FasciolideaGenus: FasciolaSpecies: hepatica

Fascioliasis:

Important parasitic disease. Caused by

• Two species:

• Fasciola hepatica• Fasciola gigantica

Fascioliasis:

Morphology: (Angus, 1978)Specie Size Shape

F.hepatica 5cm length/1.5cm wide

Leaf shape with prominent shoulders

F.gigantica 7.5cm length/1.2cm wide

Leaf shape with scarcely perceptible shoulders

Fasciola hepatica Fasciola hepatica, also known as the common liver

fluke or sheep liver fluke. Is a parasitic flatworm of the class Trematoda,

phylum Platyhelminthes that infects liver of various mammals, including humans.

The disease caused by the fluke is called fascioliasis (also known as fasciolosis).

F. hepatica is world-wide distributed and causes great economic losses in sheep and cattle.

Life cycle outside the animal Eggs hatch in spring (>10 °C) to release miracidia

which must penetrate a mud snail (Lymnaea [syn. Galba] truncatula) within 3 hours

Develop inside snail Cercariae emerge from snail Encyst on grass (metacercariae) Infection of a snail with one miracidium can

produce over 600 metacercariae

Life cycle inside the animal

Once ingested metacercariae excyst in SI and immature fluke migrate through the gut wall to penetrate the liver

Tunnel through liver for 6-8 weeks before entering bile ducts where they reach maturity

Time from infection of cattle/sheep to adult egg-laying fluke is 10-12 weeks

Little or no development of immunity

An overview of Life Cycle

Egg capsule with emerging miracidium of Fasciola hepatica. 400x

Clinical signs Two important clinical phases

are: Acute and chronic Clinical signs are: Fever Right-upper-quadrant pain Nausea Anorexia Jaundice Biliary obstruction Anemia

Condemned LiverAnnual condemnation of livers of 3-4% of cattle at $3-5 each due to parasites.

•Adult-Biliary hyperplasia, dilatation, fibrosis, calcification•Migration-Diffuse fibrosis, shrunken ventral lobe

Cattle: Partial immunity builds, self-cure at 5-8 months after major infection, most gone within 1 year.

Sheep and goats: Little immunity, flukes live up to 10 years

Rabbit, swine, other ‘incidental’ hosts are potential reservoirs

Zoonotic human infection via watercress, vegetables is a major problem in the altiplano of the Andes, Egypt, Iran, sporadic elsewhere

Habitats are shallow depressions (eg. imperfections in ‘ditch and crown’ drainage systems seen here) that stay wet half the year and freshen with each rain. Lymnaeid snail hosts are found on mud at the edge of habitats. Rain stimulates shedding of cercariae by snails, a dispersal adaptation that helps spread infection to a larger area of the pasture. Most infections are focal, in and around snail habitats.

Snail Habitat

Fluke with Spines of flukes in bile ducts erode proliferated epithelium and consume blood and exudate. Proline, a by-product of the incomplete metabolism of Fasciola, rises to 1000 times normal. Proline excess has been shown to lead to bile duct fibrosis and depression anemia experimentally. Fasciola consumes only 0.2 ml blood/fluke/day, not enough for the anemia, hypoproteinemia seen with heavy fluke infections.

Pathogenesis

Heavily Parasitized Heifer

Sub acute clinical infections are seldom seen in cattle, associated with burdens of >200 flukes. Chronic sub-clinical disease is typical. Most fluke effects occur 6-20 weeks after heavy exposure (after entry to bile ducts), then lessen. An 8-28% reduction in rate of gain has been reported in feeder calves infected with 40-140 flukes. Minor effects with <10 flukes.

Bacillary hemoglobinuria is predisposed by fluke migration anaerobic tracts.

In some geographic areas of the west, vaccination of cattle must be given each 6 months where soils favor persistence of Clostridium hemolyticum. Cl. Novyi causes ‘Black disease’, with multifocal lesions.

Anaerobic bacteria proliferate in necrotic tracts and produce potent exotoxins and acute death.

Liver infarct, Bacillary Hemoglobinuria

Diagnosis

Fasciola is diagnosed by fecal sedimentation examination

Eggs are large, operculated and golden in color

Treatment_____________________________________________________

Bile duct Bile duct Parenchyma Drug Adults Immature Migratory

Hexachloroethane* 90% ? -

Albendazole 10mg/kg 75-90% 33% -

Clorsulon 7mg/kg >99% 96% -

in Ivomec+ 2mg/kg >90% >70% -

Triclabendazole >99% >99% >90% (10mg/kg, available worldwide)

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*Removed from market as a carcinogen in 1985

Rationale of treatment recommendations

• Treat in each region two months after transmission season ends to allow flukes to become adult and susceptible to available drugs, but while still in maximum pathogenic phase

•The end of season can be determined by producers when habitats dry up for >2 weeks in summer-fall or when sustained periods of winter cold <10 C begin.

Herd egg count monitoring

Interpretation % Prevalence Mean EP2G

Low burden < 25 % < 1 (No economic losses)

Moderate Burden 25-75% 1-3(Economic Loss Possible)

Heavy Burden 75-90% 3-10(Economic loss probable)

Economical >90% >10 ________________________________________________