Causative Agent of Fascioliasis

• The causative agent of Fascioliasis is a trematodes Fasciola hepatica also termed as the common liver fluke or the sheep liver fluke and Fasciola gigantica are large liver flukes.
• These are mainly found in domestic and wild ruminants and are causal agents of fascioliasis in humans.

Morphology of Fasciola

• F. hepatica up to 30 mm in wide and 15 mm long while F. gigantica is up to 75 mm by 15 mm.
• An adult Worm is about 30mm in length and 13 mm in width.
• It is considered as the largest fluke in the world.
• The adult worm is leaf shaped with the anterior end being broader than the posterior end and contains an anterior cone-shaped projection. 
• The anterior cone contains a powerful oral sucker at the terminal end and a ventral sucker at the base of the cone. This helps in attachment with the lining of the biliary ducts.
• They contain highly branched ovaries and testes, these help in the formation of eggs.
• The eggs are operculated and average 140 μm in length and 75 μm in width.

Scientific Classification

Epidemiology of Fasciola

• There are almost 70 countries affected by Fasciola and all of them are in continents except Antarctica.
• It is also found in a different parts of Latin America, the Caribbean, Europe, the Middle East, Africa, Asia, and Oceania.
• About 180 million people at risk and an estimated 2.4 million people now infected worldwide by this parasite.
• Most human cases are found in the Andean highlands of Bolivia and Peru.
• These parasites are mainly found in those locations where sheep and cattle are present in huge numbers and in their dietary habits include the consumption of raw aquatic vegetables. Such locations are  Portugal, the Nile delta, northern Iran, parts of China, and the Andean highlands of Ecuador, Bolivia, and Peru.

Transmission of Fascioliasis

• There is no specific vector for the transmission of Fascioliasis. This infection is only transmitted when anyone consumes contaminated raw, fresh-water vegetation.
• Most of the cases occur due to watercress consumption, although alfalfa and water lettuce play a large role is some areas. 
• The plant can be infected if the body water on which the vegetation is growing is get contaminated by eggs in the fecal matter of an infected host. 
• In Middle East, a form of infection called halzoun is contracted by eating the raw liver of an infected animal

Host/Reservoir of Fascioliasis

• Humans are the accidental hosts of the Fasciola hepatica parasite.
• The domestic and wild ruminants are the primary definitive hosts of Fasciola.
• It also found in several mammalian herbivores.

Fascioliasis life cycle/ Pathogenesis of fascioliasis

1. First of all the immature eggs are released in the biliary ducts and passed in the stool.
2. In freshwater, it becomes embryonated which takes over ~2 weeks.
3. Now, these embryonated eggs release miracidia within the water.
4. These released miracidia invade within a suitable snail intermediate host.
5. After the invasion, the parasites undergo different developmental stages such as; sporocysts, rediae, cercariae.
6. The snail discharged the cercariae and encyst as metacercariae on aquatic vegetation or other substrates.
7. When a human or other mammals ingest this metacercariae-contaminated vegetation they got infected(e.g., watercress).
8. After ingestion, the metacercariae excyst in the duodenum and enter through the intestinal wall into the peritoneal cavity. 
9. The young flukes then through the liver parenchyma into biliary ducts, where they develop into adult flukes and produce eggs.
10. In humans, maturation from metacercariae into adult flukes normally takes about 3–4 months. The development of F. gigantica may take somewhat longer than F. hepatica.

Fascioliasis symptoms

In most cases this infection is asymptomatic, but the symptoms can appear from a few days to several years after infection. Some common symptoms are Fever [usually the first symptom of the disease; 40–42 °C (104–108 °F)]; Abdominal pain; Gastrointestinal disturbances: loss of appetite, flatulence, nausea, diarrhea; Urticaria; Respiratory symptoms (very rare): cough, dyspnoea, chest pain, hemoptysis; Hepatomegaly and splenomegaly; Ascites; Anaemia; Jaundice.

The symptoms of Fascioliasis appears in the following phases;

Acute Phase

• This phase is rare in human, only occurs of the infected human ingest large number of metacercariae at once.
• The following symptoms are developed in this phase; vomiting, diarrhea, urticaria (hives), anemia, Fever, tender hepatomegaly, and abdominal pain.
• These symptoms are developed due to the migration of the F. hepatica larvae throughout the liver parenchyma.
• The worms puncture into the liver capsule and initiate the development of the following symptoms within 4-7 days after ingestion. This phase is continued for 6-8 weeks until the larvae grow and settle in the bile ducts.

Chronic Phase ­

• The following symptoms are developed in this phase; biliary cholic, abdominal pain, tender hepatomegaly, jaundice, and in children, severe anemia. All of these symptoms are common in humans.
• These manifestations indicate the biliary difficulty and swelling due to the presence of a large number of adult worms and their metabolic waste in the bile ducts.
• Swelling of the bile ducts can result in fibrosis and an infirmity termed “pipestem liver”; a white appearance of the biliary ducts after fibrosis. 
• The final consequence of severe infections is portal cirrhosis and even death.

Halzoun 

• In this phase, the worm settles in the pharynx. This phase mainly occurs when someone consumes an infected raw liver.
• The fresh adult worms get attach to the pharyngeal mucosa, then it results in considerable pain, edema, and bleeding that can conflict with respiration.

Ectopic Infection

• ­Ectopic infections by conventional transmission are rare but can transpire in the peritoneal cavity, intestinal wall, lungs, subcutaneous tissue, and very rarely in other places.

Diagnosis of Fascioliasis

• The diagnosis is done by searching for Fasciola eggs in stool (fecal) specimens, duodenal aspirate or biliary aspirate.
• The flukes initiate the formation of eggs after roughly 4 months of infection. We can not examine stools until this time passed because in the case of ectopic infections where eggs are not present in the stool. So, we can perform serological tests to detect them such as FAST-ELISA.
• Ultrasound can be used to visualize adult flukes in the bile ducts. 
• CT scan can reveal burrow tracts made by the worms.

Fascioliasis treatment

• For Treatment of Fascioliasis, many countries use a 5-10 day course of oral bithionol at 30mg/kg body weight.
• The antihelmintic agent, Triclabendazole can be preferred. It is a member of the benzimidazole family of anthelmintics. The resistance is rising to this drug
• The Artemether has been shown to be effective in a rat model of fascioliasis.
• Simultaneously with pharmaceutical therapy, surgery may be essential in very extreme cases to clear the biliary tract.

Fascioliasis Prevention and Control

Currently, there is no vaccine developed against Fascioliasis infection.