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Fascioliasis

Liver fluke disease

Overview

Fascioliasis is a rare infectious disorder caused by caused by the common liver fluke Fasciola hepatica as well as by Fasciola gigantica. These parasites are liver flukes that live in plant-eating animals. Liver flukes can be found on water plants in certain parts of the world. When the parasite invades the liver, bile passages may be blocked. A subdivision of Fascioliasis called Halzoun Syndrome affects the throat (pharynx). This infection can usually be controlled and/or cured with timely treatment.

Symptoms - Fascioliasis

The disease has three phases: acute, latent, and chronic. The acute phase begins approximately four days after infection and can last for two to four months. Symptoms during this phase include fever, abdominal pain with tender liver, gastrointestinal disturbances, and hives (urticaria) accompanied by bouts of bronchial asthma. The latent phase begins when mature flukes reach the bile duct and can last for several months. Individuals in this phase are asymptomatic. The chronic phase can persist for several years. Symptoms include gastrointestinal pain, fatty food intolerance, nausea, jaundice, itching, and abdominal tenderness.

Causes - Fascioliasis

Fascioliasis is caused by infection with the parasitic worms of the genus Fasciola, of which "Fasciola hepatica", found in temperate climates, and "Fasciola gigantica", found in tropical climates, are the most common. Encysted parasitic larvae of these parasites live on water plants, such as watercress, that may be eaten by man or eaten by animals that subsequently are eaten by man. Once ingested, the larvae escape from the cysts in the small intestine and migrate across the intestinal wall into the abdominal cavity. They transform into immature worms and, once they reach the liver, move around for up to six weeks, feeding on liver tissue. Eventually, they take up residence in the bile ducts, where they cause lesions and chronic liver disease. Generally, the parasite can be killed by adequate cooking of foods before they are eaten.

Prevention - Fascioliasis

In some areas special control programs are in place or have been planned. The types of control measures depend on the setting (such as epidemiologic, ecologic, and cultural factors). Strict control of the growth and sale of watercress and other edible water plants is important. Individual people can protect themselves by not eating raw watercress and other water plants, especially from endemic grazing areas. Travelers to areas with poor sanitation should avoid food and water that might be contaminated (tainted). Vegetables grown in fields, that might have been irrigated with polluted water, should be thoroughly cooked, as should viscera from potentially infected animals.

Diagnosis - Fascioliasis

Most immunodiagnostic tests will detect infection and have a sensitivity above 90% during all stages of the diseases. In addition antibody concentration quickly drops post treatment and no antibodies are present one year after treatment, which makes it a very good diagnostic method. In humans, diagnosis of fasciolosis is usually achieved parasitologically by findings the fluke eggs in stool, and immunologically by ELISA and Western blot. Coprological examinations of stool alone are generally not adequate because infected humans have important clinical presentations long before eggs are found in the stools.

Moreover, in many human infections, the fluke eggs are often not found in the faeces, even after multiple faecal examinations. Furthermore, eggs of F. hepatica, F. gigantica and Fasciolopsis buski are morphologically indistinguishable. Therefore, immunonological methods such ELISA and enzyme-linked immunoelectrotransfer blot, also called Western blot, are the most important methods in diagnosis of F. hepatica infection. These immunological tests are based on detection of species-specific antibodies from sera. The antigenic preparations used have been primarily derived from extracts of excretory/secretory products from adult worms, or with partially purified fractions. Recently, purified native and recombinant antigens have been used, e.g. recombinant F. hepatica cathepsin L-like protease.

Methods based on antigen detection (circulating in serum or in faeces) are less frequent. In addition, biochemical and haematological examinations of human sera support the exact diagnosis (eosinophilia, elevation of liver enzymes). Ultrasonography and xray of the abdominal cavity, biopsy of liver, and gallbladder punctuate can also be used (ref: US-guided gallbladder aspiration: a new diagnostic method for biliary fascioliasis. A. Kabaalioglu, A. Apaydin, T. Sindel, E. Lüleci. Eur. Radiol. 9, 880±882 (1999) . False fasciolosis (pseudofasciolosis) refers to the presence of eggs in the stool resulting not from an actual infection but from recent ingestion of infected livers containing eggs. This situation (with its potential for misdiagnosis) can be avoided by having the patient follow a liver-free diet several days before a repeat stool examination.

In animals, intravital diagnosis is based predominantly on faeces examinations and immunological methods. However, clinical signs, biochemical and haematological profile, season, climate conditions, epidemiology situation, and examinations of snails must be considered. Similarly to humans, faeces examinations are not reliable. Moreover, the fluke eggs are detectable in faeces 8–12 weeks post-infection. In spite of that fact, faecal examination is still the only used diagnostic tool in some countries. While coprological diagnosis of fasciolosis is possible from 8- to 12-week post-infection (WPI), F. hepatica specific-antibodies are recognized using ELISA or Western blot after 2-4 week post-infection. Therefore, these methods provide early detection of the infection.

Prognosis - Fascioliasis

Not supplied.

Treatment - Fascioliasis

Several drugs are effective for fascioliasis, both in humans and in domestic animals. The drug of choice in the treatment of fasciolosis is triclabendazole, a member of the benzimidazole family of anthelmintics. The drug works by preventing the polymerization of the molecule tubulin into the cytoskeletal structures, microtubules. Resistance of F. hepatica to triclabendazole has been recorded in Australia in 1995 and Ireland in 1998.

Praziquantel treatment is ineffective. There are case reports of nitazoxanide being successfully used in human fasciolosis treatment in Mexico. There are also reports of bithionol being used successfully.

Nitazoxanide has been found effective in trials, but is currently not recommended. The life cycle includes freshwater snails as an intermediate host of the parasite.

Resources - Fascioliasis

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