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Endoparasites - Fasciola

Fasciola hepatica: Common liver fluke

General Description: Fasciola hepatica adults are greyish brown, leaf-shaped flukes as large as 30 by 13 mm. The anterior end has a cone-shaped projection, behind which the fluke´s broad "shoulders" begin.

Life Cycle: Adult flukes in the liver lay eggs in the bile, which carries them into the intestine. They leave in the host´s faeces. After hatching, the immature fluke must penetrate a snail for the life cycle to continue. Multiplication occurs within particular species of snail. After leaving the snail they encyst on grass where they are eaten by horses. The young parasites penetrate the gut and pass to the liver. The snails live in swampy, wet areas.

Location: Bile ducts.

Geographical Distribution: Fasciola hepatica occurs worldwide in wet areas where Lymnaea snails may exist. It is not a significant problem in New Zealand.

Significance: Animals experience anaemia and decreased growth. Liver damage results in organ condemnation at slaughter.

Effect on Host: Migration of flukes in the liver damages the tissue, resulting in formation of scar tissue, disrupting normal liver function and thus decreasing production of albumin. Tissue destruction and bile duct irritation by the fluke´s spines necessitate considerable cell replacement. The host´s inability to achieve complete cell replacement allows leakage of blood proteins into the bile and intestine. Flukes also ingest red blood cells directly, causing iron-deficiency anaemia if the animal´s iron stores are exhausted by replacing lost cells. The combination of these conditions over a prolonged period causes decreased growth, weight loss, anaemia, and edema.

Diagnostic Information: Fasciola eggs are larger than those of strongyles, and are 140 by 63 to 90 microns. Presence of these eggs in faeces indicates a fluke infection.

Control: Snails must be eliminated from pasture by draining water and applying copper sulfate to the pasture. Infected animals are treated with a flukicide which will reduce pasture contamination.


 
Fasciola– adult   Metacercariae
     
 
Snail   Fluke egg

       

 

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