Fasciola Hepatica

Synonyms: Liver fluke, liver rot.

Fasciola hepatica is a parasite that infests humans and many species of animals. It is in the phylum Platyhelminthes (flatworms), class Trematodea (flukes), sub class Digenea. Fasciola hepatica is the usual cause of fascioliasis.

This is one of the largest flukes, measuring up to 3.5cm by 1.5cm. The parasite lives in the liver and bile duct. Its hosts include herbivorous mammals and it is found in 46 species of domestic and wild animals as well as man.

Its intermediate host is the Lymnaea snail which lives in marshy areas and standing water. In the adult stage, they have a large leaf-shaped body.

It causes "liver rot" in sheep and cattle.

Fasciola gigantica may also cause similar human disease, and several other species cause disease in animals. F. halli and F. californica infest sheep and cattle in the USA and may be synonymous with F. jacksoni that infests elephants in Africa & India, F. nyanzae whose host is the hippopotamus, and F. magna that infests mostly deer, but also cattle and sheep.

• It is found in all continents except Antarctica.
• It is one of the most economically important parasitic diseases of livestock, causing disease in sheep and other domestic animals in Latin America, Africa, Europe, and China.
• Of the 750 million people who live in endemic areas, over 40 million are thought to be infected.¹ It is commonest in Bolivia, Ecuador, Egypt and Peru, but is also found in European countries including France, United Kingdom, Spain and Portugal. The incidence has apparently increased over the last 20 years.
• It affects ruminants much more than man.
• Infestation is by eating watercress and other contaminated aquatic plants.

• Animals eat plants such as watercress that are contaminated by the metacercariae form of the parasite.
• The larvae encyst in the duodenum and penetrate the intestinal wall, peritoneal cavity and liver capsule to reach the bile duct where they mature into adult worms. This takes 6 to 8 weeks.
• The adult lays eggs which are excreted in the faeces.
• The next stage occurs in freshwater where after about a month, a miracidium hatches from the egg and invades the intermediate, snail host. In the snail, the larva multiplies asexually through a single generation of sporocysts and 2 generations of rediae, to develop into cercariae, the process taking 5 to 7 weeks.
• The cercariae leave the snail when conditions are optimal. This means moist conditions with a temperature of at least 10°C, and encyst on aquatic plants to form metacercariae. They can survive in high humidity and cool conditions for up to a year.
• When animals or humans eat these plants, they become infected and the life cycle is repeated.
• Infection by consumption of raw liver from infected sheep, goats, and cows has been reported.

Although seen typically as a disease of developing countries, it does present in Europe and the developed world.²

Acute Fascioliasis

• In its severe form it occurs in sheep but rarely in man and requires large numbers of parasites, usually over 10,000, to be ingested. Large numbers of migrating larvae invade the liver and cause a traumatic hepatitis that is frequently fatal. Sometimes the liver capsule may rupture into the peritoneal cavity causing death from peritonitis.
• More usually the invasive phase lasts many weeks, with the commonest symptoms being intermittent fever, hepatomegaly, and abdominal pain,³ although up to 50% of infections may be subclinical.
• Abdominal pain is usually in the epigastrium or right hypochonrium.
• Other symptoms include malaise and wasting. Urticaria and eosinophilia are usual.

Chronic Fascioliasis

• After reaching the liver, there is then a latent phase lasting months or even years, when infection is asymptomatic,
• However with maturation there may be an obstructive phase causing hepatitis, cholangitis, or pancreatitis. Fasciola spp are not adapted to using man as a definitive host and so the flukes may cause ectopic infections, especially in the lungs and subcutaneous tissues where they may form cysts.
• Halzoun is one such type of infection following consumption of raw liver. There is severe pharyngitis, dysphagia, sensation of a foreign body in the throat and possibly airways obstruction.

The potential list is vast, but amongst it are:

• Various forms of hepatitis
• Amoebiasis
• Leishmaniasis
• Schistosomiasis

• FBC will show eosinophilia and probably anaemia. Eosinphilia occurs in 95% in the acute phase but may be variable in the chronic disease.
• About half have an elevated ESR.
• LFTs may show evidence of hepatocellular damage from parasites, or evidence of obstruction.
• Stool microscopy may show the pathogen or the eggs.
• Various immunoassays are available and ELISA tests are very sensitive and specific.⁴ They may turn positive before microscopy of the stool but they may give false positives based on past rather than current infection.
• X-ray of the liver may show tract-like small abscesses and sub-capsular lesions.
• Even with pulmonary symptoms, chest x-ray is rarely rewarding.
• Ultrasound of the gall bladder and biliary tract may show adult worms as focal areas of increased echogenicity.⁵
• Cholangiography may reveal multiple cystic dilatations of the ducts. Large cystic dilatation, small cystic ectasia, and mulberry-like dilatation are considered diagnostic of fascioliasis.

Non-Drug

Bed rest and a protein-rich diet are recommended. Iron and vitamins may be required.

Drugs

If dealing with such a case, seek expert advice. Bithionol is the drug of choice⁶ but is not in the BNF and may need to be presrcibed on a named patient basis.

• Bithionol, 30 to 50 mg/kg orally on alternate days for 10 to 15 doses. Bithionol is the drug of choice or praziquantel when bithionol is not available or fails. Treatment reverses damage to the structure of the liver.⁷
• Triclabendazole is increasingly being used, and metronidazole has had some success where this fails.
• Myrrh (mirazid) has also been used.

Surgical

• Parasite removal at endoscopic retrograde cholangiopancreatography is effective in the biliary stage.
• Ascending cholangitis may require surgery.

• It is often associated with anaemia, especially in children.
• Biliary fibrosis.
• Cholangiocarcinoma can occur rarely.

The disease rarely kills in humans. Treatment produces good results.

• Water-grown vegetables should be washed with 6% vinegar or potassium permanganate for 5-10 minutes which kills the encysted metacercariae. This approach is more successful than attempts to halt the consumption of raw vegetables.
• Cook water-grown vegetables thoroughly before eating.
• Avoid sewage contamination of growing areas.
• Molluscicides is the most frequent public health intervention, as it prevents the transmission of many other trematodes, including Schistosoma spp.
• Treatment of animals to reduce the reservoir and reduce stock losses has been used. Until the introduction of single-dose triclabendazole, bithionol was the only available treatment, much limited by expense and treatment duration.
• For the future, vaccination would⁸ seem to be a feasible option.

Evidence of infection in humans has been found in wetland prehistoric sites in Europe as far back as 3500BC, and is likely to be as old as the practice of herding.

Sheep fluke was the first fluke or trematode to be identified, credit going to the frenchman, Jehan de Brie, in his 1379 publication, Le Bon Berger (The Good Shepherd).

Linnaeus gave it the latin name, Fasciola hepatica, in 1758.

Work into the natural history was stimulated by an outbreak of liver rot in Britain, which killed over 3 million sheep in 1879-80. Within a year, A P W Thomas (Balliol College Oxford), and Rudolf Leuckart in Germany (zoologist and teacher, and the founding father of the science of parasitology), independently elucidated the complex life cycle.