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Fascioliasis

WHO/P. Virot

Fascioliasis is caused by trematodes belonging to the genus Fasciola (F. hepatica and F. gigantica).

In the past, infection was limited to specific and typical geographical areas, but is now widespread throughout the world. Human cases are increasingly reported from Europe, the Americas and Oceania (where only F. hepatica is transmitted), and from Africa and Asia (where the two species overlap). If it was previously believed that humans became infected only occasionally from livestock, evidence now suggests that there are endemic foci in which human-to-human transmission may occur. As a consequence, human fascioliasis should be considered a disease of major global public health importance.

Fascioliasis is a zoonosis, i.e. a disease of animals that can be transmitted to humans. Susceptible animal reservoir hosts for Fasciola species include:

• the main domestic animals: cattle, sheep, pigs, buffaloes and donkeys;
• other domestic animals: horses, goats, dromedaries, camels and llamas;
• sylvatic animals (hares, rabbits and rodents).

The mode of transmission is the faecal–oral route. Parasite eggs are passed in the faeces of infected animals or humans and contaminate water where they develop within snails. The snails release mature larvae that attach to vegetation and encyst as metacercariae.

Humans typically become infected by ingesting encysted metacercariae attached to aquatic or semi-aquatic plants. Evidence also indicates that infection may occur by drinking water contaminated with floating metacercariae and by ingesting metacercariae attached to the surface of food or kitchen utensils washed with water contaminated with floated metacercariae.

Fascioliasis is a serious medical condition due to the size of the parasite which reflects its origin as a livestock worm (adult F. hepatica measure 20–30 mm x 13 mm wide, while adult F. gigantica measure 25–75 mm x 12 mm wide). After an incubation phase lasting days to a couple of months, human fascioliasis can be distinguished by an acute and a chronic phase. The acute phase is characterized by the migration of immature worms through the liver; symptoms are related to haemorrhage and inflammation and are usually severe, including fever, abdominal pain, respiratory disturbances and skin rashes. The chronic phase starts when the worms reach the bile ducts; symptoms are nonspecific and usually mild. Progressive inflammation, however, leads to fibrosis and thickening of the walls of the ducts and gallbladder that eventually may result in progressive blockage due to parasites, parasite fragments or debris. In this case, biliary colic pain is a characteristic symptom. Chronic infections may result in biliary cirrhosis with scarring and fibrosis of the liver and growth deficiencies.

Triclabendazole 10 mg/kg body weight single dose is the regimen of choice against fascioliasis. The drug is active against both immature and adult parasites, with high cure rates. Adverse reactions following treatment are usually temporary and mild.

New opportunities for control

WHO and Novartis Pharma AG have negotiated an agreement whereby Novartis will donate triclabendazole for the treatment of infected individuals in endemic countries. The drug will be available free of charge to such countries upon application from ministries of health.

Ministries of health in affected developing countries are invited to take advantage of this landmark donation programme.
No continent is free from fascioliasis, and it is likely that where animal cases are reported, human cases also exist.
Only with a reasonable triclabendazole stockpile, will ministries of health be in a position to (1) supply their hospitals with enough drugs to allow their health staff to treat self-reported cases and (2) plan and implement large-scale drug distributions if fascioliasis is found to be an important public health problem.

For further information:

• WHO Informal Meeting on use of triclabendazole in fascioliasis control
  WHO headquarters, Geneva, 17–18 October 2006
• Food-borne trematode infections in Asia
  Report of a joint WHO/FAO workshop, Ha Noi, Viet Nam, 26-28 November 2002
  World Health Organization, WPRO
• Control of foodborne trematode infections - Report of a WHO study group. Part 1.
  and Part 2.
  WHO Report Technical Series, ISBN: 92 4 120849 X
• "Action Against Worms" – Issue 10
  This issue of "Action Against Worms" is about fascioliasis, one of the most neglected tropical diseases, which however represents a significant public health problem in many parts of the world.

or contact the programme on Fascioliasis at: fasciola@who.int