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Fasciolosis
Fasciolosis (also known as fascioliasis, fasciolasis, distomatosis and liver rot) is a parasitic worm infection caused by the common liver fluke ''Fasciola hepatica'' as well as by ''Fasciola gigantica''. The disease is a plant-borne trematode zoonosis, and is classified as a Neglected Tropical Disease (NTD).〔 It affects humans, but its main host is ruminants such as cattle and sheep.〔 The disease progresses through four distinct phases; an initial incubation phase of between a few days up to three months with little or no symptoms; an invasive or acute phase which may manifest with: fever, malaise, abdominal pain, gastrointestinal symptoms, urticaria, anemia, jaundice, and respiratory symptoms. The disease later progresses to a latent phase with less symptoms and ultimately into a chronic or obstructive phase months to years later.〔Esteban, J.G., Bargues, M.D., Mas-Coma, S., 1998. "Geographical distribution, diagnosis and treatment of human fascioliasis: a review". Res. Rev. Parasitol. 58, 13–42.〕 In the chronic state the disease causes inflammation of the bile ducts, gall bladder and may cause gall stones as well as fibrosis.〔 While chronic inflammation is connected to increased cancer rates it is unclear whether fasciolosis is associated with increased cancer risk.
Up to half of those infected display no symptoms,〔 and diagnosis is difficult because eggs are often missed in fecal examination. The methods of detection are through fecal examination, parasite-specific antibody detection, radiological diagnosis as well as laparotomy. In case of a suspected outbreak it may be useful to keep track of dietary history, which is also useful for exclusion of differential diagnoses.〔 Fecal examination is generally not helpful because eggs can seldom be detected in the chronic phase of the infection and detection of eggs. Eggs appear in the feces first between 9–11 weeks post-infection. The cause of this is unknown, and the it is also difficult to distinguish between the different species of fasciola as well distinguishing them from Echinostomes and Fasciolopsis.〔 Most immunodiagnostic tests detect infection with very high sensitivity and as concentration drops after treatment it is a very good diagnostic method.〔 Clinically it is not possible to differentiate from other liver and bile diseases. Radiological methods can detect lesions in both acute and chronic infection, while laparotomy will detect lesions and also occasionally eggs and live worms.〔
Because of the size of the parasite (adult ''F. hepatica'': 20–30 × 13 mm, adult ''F. gigantica:'' 25–75×12 mm) fasciolosis is a big concern.〔 The amount of symptoms depend on how many worms and what stage the infection is in. The death rate is significant in both sheep and cattle, but generally low among humans. Treatment with triclabendazole is highly effective against the adult worms as well as various developing stages.〔〔 Praziquantel is not effective, and older drugs such as bithionol are moderately effective but also cause more side effects. Secondary bacterial infection causing cholangitis is also a concern and can be treated with antibiotics, and toxaemia may be treated with prednisolone.〔
Humans are infected by eating watergrown plants, primarily wild grown watercress in Europe and morning glory in Asia. Infection may also occur by drinking contaminated water with floating young fasciola or when using utensils washed with contaminated water.〔 Cultivated plants do not spread the disease in the same capacity. Human infection is rare even if the infection rate is high among animals. Especially high rates of human infection have been found in Bolivia, Peru and Egypt, and this may be due to consumption of certain foods.〔 No vaccine is available to protect people against ''Fasciola'' infection. Preventative measures are primarily treating and immunization the livestock – which are required for the live cycle of the worms. Veterinary vaccines are in development and their use is being considered by a number of countries on account of the risk to human health and economic losses resulting from livestock infection.〔 Other methods include using molluscicides to decrease the amount of snails that act as vectors, but it is not practical.〔 Educational methods to decrease consumption of wild watercress and other waterplants has been shown to work in areas with a high disease burden.〔 In some areas of the world where fascioliasis is found (endemic), special control programs are in place or are 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.〔 Fascioliasis occurs in Europe, Africa, the Americas as well as Oceania.〔 Recently, worldwide losses in animal productivity due to fasciolosis were conservatively estimated at over US$3.2 billion per annum. Fasciolosis is now recognized as an emerging human disease: the World Health Organization (WHO) has estimated that 2.4 million people are infected with ''Fasciola'', and a further 180 million are at risk of infection.〔Anonymus 1995. Control of Foodborne Trematode Infections. WHO Technical Series No. 849. WHO, Geneva, 157 pp.〕
==Signs and symptoms==
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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