TREMATODA Fasciola hepatica

Introduction Trematodes are flukes: Class Trematoda; Phylum Platyhelminthes. Subclass: Digenea, Order: Protostomata,

Suborder: Strigeata genus Schistosoma

Suborder :Distomata genus Fasciolopsis, Opisthorchis, Clonorchis,

Paragonimus.

Cont… Some specific examples include:

Fasciola hepatica ( liver fluke)Clonorchis sinensis (liver)Fasciolopsis buski (intestinal)Paragonimus westermani (lung)Schistosoma spp. (blood).

Fasciola hepatica "sheep liver fluke," is misleading since this parasite is found in

animals other than sheep (including cattle and humans), resides in the bile ducts inside the liver. adult reside in the intrahepatic bile ducts, produce eggs, and the

eggs are passed in the host's feces. Transmission

through the ingestion of raw, fresh-water vegetation on which the flukes in their metacercariae form are encysted.

The plants become exposed to the metacercariae when the body of water that the vegetation is growing in becomes contaminated by eggs in the fecal matter of an infected host.

Nearly all cases are a result of watercress consumption beside alfalfa and water lettuce.

The Adult one of the largest flukes in the world. 20 -30mm in length and 13 mm in width Leaf shape characteristic with the

anterior end broader than the posterior end and an anterior cone-shaped projection.

Possesses a powerful oral sucker at the anterior cone and a ventral sucker at the base of the cone attach to the lining of the biliary ducts.

monoecious - possesses ovaries and testes which are highly branched and allow for individual flukes to produce eggs independently.

A stained adult Fasciola hepatica; approximate length = 20 mm.  The internal organs are highly branched, thus making it very difficult to differentiate the various internal organs

All of their major systems are branched, including the intestine, testes, and ovary.

The ova

Length 130-145 µmWidth 70-90 µmRegular ellipseThin shellOperculum at one poleGranular yellowish-brown contents filling whole egg

egg capsule with emerging miracidium of Fasciola hepatica.  400x

unembryonated egg capsule of F. hepatica. earlier stage of development.  400x

embryonated egg capsule of Fasciola hepatica.  So-named because the miracidium is fully formed and ready to emerge.  The operculum can be seen to the left.  400x

Redia and cercaria of Fasciola hepatica

Miracidium of Fasciola hepatica. This ciliated, non-feeding larval stage, has about 24 hours to find its specific snail host, such as Fossaria modicella or Stagnicola bulimoides.  400x

The Life Cycle

Cont.. Eggs passed in the feces develop into miracidia in ~2-4

wk, depending on temperature, and hatch in water. Miracidia infect lymnaeid snails, in which development

and multiplication occur through the stages of sporocysts rediae (sometimes daughter rediae) cercariae.

After ~2 mo (or longer if temperatures are low), cercariae emerge from snails and encyst on aquatic vegetation.

Encysted cercariae (metacercariae) may remain viable for many months unless they become desiccated.

Cont.. After ingestion by the host, usually with herbage, young flukes

are released in the duodenum, penetrate the intestinal wall, and enter the peritoneal cavity.

The young flukes penetrate the liver capsule and wander in the parenchyma for several weeks, growing and destroying tissue.

They enter the bile ducts, mature, and begin to produce eggs. The prepatent period is usually 2-3 mo, depending on the fluke burden.

Adult flukes may live in the bile ducts of sheep for years; most are shed from cattle within 5-6 mo. Prenatal infections have been reported in cattle.

Pathogenecity & Symptoms ~50% asymptomatic disease may appear anywhere from a few days to several

years after infection Eosinophilia is present with all infections at all stages and

can be used as a diagnostic factor in ectopic and early stage infections when eggs are not be present in the stool.

When symptoms do appear, they occur in the following patterns:

Acute Phase: Rarely seen in humans and occurs only when a large

number of metacercariae are ingested at once. Fever, tender hepatomegaly, and abdominal pain are

the most frequent symptoms of this stage of infection

vomiting, diarrhea, urticaria (hives), anemia, may be present.

Caused by the migration of the F. hepatica larvae throughout the liver parenchyma.

The larvae penetrate the liver capsule and begin to produce symptoms 4-7 days after ingestion.

Migration and acute phase continues for 6-8 weeks until the larvae mature and settle in the bile ducts.

Cont.. Chronic Phase:

more common in human include biliary cholic, abdominal pain, tender

hepatomegaly, and jaundice. In children, severe anemia - common result of infection biliary obstruction and inflammation caused by the

presence of the large adult worms and their metabolic waste in the bile ducts.

Inflammation of the bile ducts leads to fibrosis and a condition called "pipestem liver", (white appearance of the biliary ducts after fibrosis).

The final outcome portal cirrhosis and even death.

Cont.. Halzoun : worm settles in the pharynx. Occurs when an individual consumes infected raw

liver The young adult worms then attach themselves to the pharyngeal mucosa causes considerable pain, edema, and bleeding that can interfere with respiration.

The adults can live in the biliary ducts, causing symptoms for up to 10 years.

Ectopic Infection: Ectopic infections through normal transmission are infrequent but can occur in the peritoneal cavity, intestinal wall, lungs, subcutaneous tissue, and very rarely in other locations.

Laboratory diagnosis The definitive and most widely used form of diagnosis is the directly

observed presence of Fasciola hepatica eggs either in a stool sample, duodenal aspirate or biliary aspirate.

However, the flukes do not begin to produce eggs until roughly 4 months after infection.

Until this time and in the case of ectopic infections where eggs are not present in the stool, serological tests can be used, the FAST-ELISA being the most popular.

It has a sensitivity of 95% and can detect specific F. hepatic antibodies as early as 2 weeks after infection .

Ultrasound can be used to visualize the adult flukes in the bile ducts CT scan may reveal the burrow tracts made by the worms and

dilation of the bile ducts.

Treatment Fascioliasis has a 80-100% success rate -

Bithionol & Triclabendazole, an antihelmintic agent.

Along with pharmaceutical therapy, surgery may be necessary in very extreme cases to clear the biliary tract.

Prevention The presence of a substantial reservoir - keep domestic

animal herds separate from the growing sites of aquatic. This limits the risk of contaminating the vegetation and thus decreases both human infection and the animal reservoir

The presence of the intermediate host, the Lymanaea snails - application of molluscicides to decrease the population of Lymnaea snails.

The opportunity for water source contamination by human and non-human hosts

Dietary practices that include the consumption of raw, untreated aquatic vegetation.

Next : Fasciolopsis buski