Fasciola hepatica is a Trematode that causes Fascioliasis or sheep liver fluke disease.
Diagnosis / Pathology
Fasciola hepatica infections produce symptoms depending on the worm load as well as the location of the worms and migration of metacercarial larva. Symptoms related to the liver (hepatomegaly and jaundice) are most common due to damage of the metacercarial larva migrating through the liver parenchyma. The migratory phase may produce symptoms such as epigastric and right upper quadrant pain, fever, and intestinal complaints. Loss of appetite, diarrhea, nausea, flatulence and sometimes even a nonproductive cough can also present. Anemia can be present and as with most helminth infections an eosinophilia accompanied by a leukocytosis is not uncommon.
The worms can produce a large amount of damage to the bile ducts due to chronic mechanical irritation and the production of damaging metabolic byproducts. The result can be hyperplasia of the biliary epithelium and fibrosis of the ducts with portal or total biliary obstruction.
The worms can also be found, though not as common, in other areas of the body such as (but not limited to) the skin, heart, lungs, intestinal wall, and brain. Infections in these sites will produce symptoms related to those sites.
Location in the Host
Fasciola hepatica is located in the bile ducts of the liver. However the intestinal wall, brain, heart, lungs, skin, etc.. are also locations where the worms have been found.
Fasciola hepatica has a worldwide distribution but is most common in areas where there is sheep-raising and cattle-raising as these two serve as reservoir hosts.
Fasciola hepatica is acquired by the ingestion of metacercariae on uncooked water plants that have been colonized by free-swimming cercariae (released by the intermediate host snail) that encyst on aquatic vegetation. They mature to metacercariae to be ingested by the definitive host. Man is considered an accidental host. The immature flukes encyst in the duodenum – penetrate the intestinal wall – and migrate through the liver parenchyma to the billary ducts. Here the adults produced eggs that are released in the stool and once in the water embryonate and hatch to release the miracidial form which infects the intermediate snail host.
Morphology & Diagnosis
Fasciola hepatica eggs are large at 130-150u long by 63-90u wide and are found in the feces during an ova & parasite examination. They have an ellipsoid shape to them and have a small and indistinct operculum. Gentle tapping of a Lugol’s iodine prep of concentrated feces can cause the operculum to “pop” open. The eggs are unembryonated in the passed feces.
Adults are rarely seen but for findings during surgery or their presence detected by biopsy.