Fasciola Hepatica

FASCIOLA HEPATICA

Commonly known as sheep liver fluke its adult form is localized in the bile ducts of its host.

Morphology:

Fasciola hepatica can be as large as 3cm long and 1.5 cm wide with an anterior cephalic cone. The parasite also has characteristically branched reproductive organs. Fasciola hepatic also has oral suckers used to effectively anchor the parasite in the bile cut.

Definitive host: sheep, cattle, goats, rabbits (laboratory host)

Intermediate Host: Lymnaeid snail

Humans are mostly seen as accidental hosts to this parasites and the rate of infection of humans is significantly lower.

 

 

Life Cycle

Image Source: http://www.dpd.cdc.gov/dpdx/images/ParasiteImages/A-F/Fascioliasis/Fasciola_LifeCycle.gif

 

Eggs have an incubation period of 14-17 days and hatch in water to release miracidium. The miracidium infects lymnaeid snail during its larval multiplication giving rise to cercariae. This is an important process with one miracidium giving rise to as many as 600 cercaria. The cercaria then develops into a metacercaria which is enveloped in a cyst and attaches to aquatic vegetation. Once it is ingested by a definitive host the metacercardia excyst and into the intestine. The liver fluke burrow into the liver and travel into the bile ducts where the adult fluke develops. The eggs are passed in feces contaminating the water and vegetation.

 

 

 

Symptoms

Most of the symptoms are caused by biliary obstruction. In humans most of the symptoms reported are high fever, diarrhea, chills, bile inflammation, liver enlargement, and Jaundice.

Pharyngeal form of fascioliasis can be seen among people who eat raw animal liver mostly in the Middle East with characteristic symptoms of bleeding and pain of the pharynx.

 

 

Pathogenesis

Mechanical obstruction caused by fluke results in inflammation of the bile duct. The parasite also secretes toxic chemicals that lead to irritation of liver tissue in sheep. Bacteria infection may also follow leading to more inflammation. Snails infected by the parasite also are enlarged supporting further parasitic growth.

 

Diagnosis

Fasciola hepatica eggs can be found in a stool sample or bilary aspirate. Ultrasonography can be used to observe adult worms in the liver. The damage caused by the parasite in the liver can be visualized by using endoscopy. Enzyme linked immunosorbent assay (ELISA) can be a more accurate diagnostic test to test for antigen of Fasciola hepatica.

 

Treatment

Bithionol-

Orally administered with a dose of 30-50mg/kg every other day for total dose of 10 to 15.

Side effects- skin reaction, vomiting, diarrhea, abdominal pain.

 

Praziquantel-

Daily dose of 25mg/kg (3X) for a total dose of 5-7 with minimal success in elimination of the parasite. Effective in lowering minimizing the level of infection.

 

Triclabendazole-

A dose of 10mg/kg body weight per day (2X). Perfect cure rate with a single dose is reported with minimal side effect. However, this drug has not been approved for human use in the United States.