'''肝蛭症'''（かんてつしょう、fascioliasis）とは寄生虫病であり、人獣共通感染症の一つ。

== 原因 ==
thumb|''Fasciola hepatica''成虫
Fasciola hepatica''）、巨大肝蛭（''Fasciola gigantica''）の感染を原因とする。日本では日本産肝蛭（''Fasciola'' sp.）が分布する。肝蛭とは厳密には''Fasciola hepatica''を指すが、前期の3つを合わせた用語として用いられる事が多い。中間宿主はヒメモノアラガイあるいはコシガタモノアラガイであり、終宿主は反芻類、ブタ、ヒト。

== 疫学 ==
世界各地に分布する。感染経路としては水辺の野草、水田におけるメタセルカリアの経口感染。

== 症状 ==
*ヒト
**感染初期では発熱、右上腹部痛、圧痛を伴う肝腫大、発咳、好酸球増多、肝機能異常。慢性期では不規則な発熱、貧血、好酸球増多、腹痛、消化不良、下痢、黄疸、体重減少がみられる。
*動物（感受性は羊、牛、豚の順に高い）
**羊では体重減少、腹水貯留、好酸球増多、貧血、肝機能障害がみられる。

== 診断 ==
虫卵の検出（渡辺法、時計皿法、昭和式肝蛭卵簡易検査法、ビーズ法、ホルマリン・エーテル法）、皮内反応、免疫電気泳動法、オクタロニー法。

== 治療 ==
ビチオノール、ブロムフェノフォス、ニトロキシニル、プラジカンテルが有効。

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'''Fasciolosis''' is an important liver fluke) and ''zoonoses. In Europe, the Americas and Oceania only ''F. hepatica'' is a concern, but the distributions of both species overlap in many areas of Africa and Asia.<ref name=Mas-Coma05></ref>

The definitive host range is very broad and includes many herbivorous life cycle includes freshwater snails as an intermediate host of the parasite.<ref name=Torges99>{{cite book |last=Torgerson |first=P |coauthors=Claxton J |chapter=Epidemiology and control.
|editor=Dalton, JP |title=Fasciolosis |publisher=CABI Pub |location=Wallingford, Oxon, UK |year=1999 |pages=113–49 |isbn=0-85199-260-9 }}</ref> Recently, worldwide losses in animal productivity due to fasciolosis were conservatively estimated at over US$3.2 billion per annum.<ref name=spithill99></ref> In addition, fasciolosis is now recognized as an emerging human disease: the right|thumb|300px|''Fasciola hepatica''

==Etiology==
Fasciolosis is caused by two digenetic trematodes ''F. hepatica'' and ''F. gigantica''. Adult flukes of both species are localized in the chimeric flukes (2n/3n) have been described, many of which reproduce parthenogenetically. As a result of this unclear classification, flukes in Japan are normally referred to as ''Fasciola'' spp.<ref>Sakaguchi, Y., 1980. Karyotype and gametogenesis of the common liver fluke, ''Fasciola'' sp., in Japan. Jap. J. Parasitol. 29, 507–513.</ref> Recent reports based on mitochondrial genes analysis has shown that Japanese ''Fasciola'' spp. is more closely related to ''F. gigantica'' than to ''F. hepatica''.<ref></ref> In India, a species called ''F. jacksoni'' was described in elephants.<ref>Singh, K.P., Srivastava, V.K., Prasad, A. and Pandey, A.P., 1994. Pathology due to ''Fasciola jacksoni'' in Indian elephants ''Elephas indicus''. Ind. J. Anim. Scien. 64, 802–804.</ref>

==Geographic Distribution==
Human and animal fasciolosis occurs worldwide.<ref name=Torges99/> While animal fasciolosis is distributed in countries with high cattle and sheep production, human fasciolosis occurs, excepting Western Europe, in developing countries. Fasciolosis occurs only in areas where suitable conditions for intermediate hosts exist. 

===Human fasciolosis===
Studies carried out in recent years have shown human fasciolosis to be an important public health problem.<ref name=Chen>Chen, M.G., Mott, K.E., 1990. Progress in assessment of morbidity due to Fasciola hepatica infection: a review of recent literature. Trop. Dis. Bull. 87, R1–R38.</ref> Human fasciolosis has been reported from countries in Europe, America, Asia, Africa and Oceania. The incidence of human cases has been increasing in 51 countries of the five continents.<ref name=Mas-Coma99>{{cite book |last=Mas-Coma |first=S |coauthors=Bargues MD, Esteban JG |chapter=Human fasciolosis.
|editor=Dalton, JP |title=Fasciolosis |publisher=CABI Pub |location=Wallingford, Oxon, UK |year=1999 |pages=411–34 |isbn=0-85199-260-9 }}</ref><ref name=Esteb98>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.</ref> A global analysis shows that the expected correlation between animal and human fasciolosis only appears at a basic level. High prevalences in humans are not necessarily found in areas where fasciolosis is a great veterinary problem. For instance, in South America, hyperendemics and mesoendemics are found in Bolivia and Peru where the veterinary problem is less important, while in countries such as Uruguay, Argentina, and Chile, human fasciolosis is only sporadic or hypoendemic.<ref name=Esteb98/>

====Europe====
In Europe, human fasciolosis occur mainly in Tajik Republic.<ref name=Esteb98/> Several papers referred to human fasciolosis in Turkey.<ref></ref> Recently, serological survey of human fasciolosis was performed in some parts of Turkey. The prevalence of the disease was serologically found to be 3.01% in Antalya Province, and between 0.9 and 6.1% in Isparta Province, Mediterranean region of Turkey.<ref>Demirci, M., 2003. Insanlarda epidemiyoloji. In: Tinar, R., Korkmaz, M. (Eds.), Fasciolosis. Türkiye Parazitoloji Derněgi, META Basim, Izmir, pp. 343–358 (in Turkish).</ref> In other European countries, fasciolosis is sporadic and the occurrence of the disease is usually combined with travelling to endemic areas.

====Americas====
In North America, the disease is very sporadic. In Caribbean Islands, especially in zones of Andean countries are considered to be the area with the highest prevalence of human fasciolosis in the world. Well-known human hyperendemic areas are localized predominately in the high plain called coprological and serological surveys, respectively.<ref name=Mas-Coma99/> In Peru, ''F. hepatica'' in humans occurs throughout the country. The highest prevalences were reported in Arequipa, Mantaro Valley, Cajamarca Valley, and Puno Region.<ref name=Mas-Coma05/> In other South American countries like Argentina, Uruguay, Brazil, Venezuela and Colombia, human fasciolosis appear to be sporadic, despite the high prevalences of fasciolosis in cattle.

====Africa====
In Africa, human cases of fasciolosis, except in northern parts, have not been frequently reported. The highest prevalence was recorded in Egypt where the disease is distributed in communities living in the Nile Delta.<ref name=Mas-Coma05/>

====Asia====
In Asia, the most human cases were reported in Iran, especially in Gīlān Province, on the Caspian Sea. It was mentioned that more than 10,000 human cases were detected in Iran. In eastern Asia, human fasciolosis appears to be sporadic. Few cases were documented in Japan, Koreas, Vietnam, and Thailand.<ref name=Mas-Coma99/>

====Australia and the Oceania====
In Australia, human fasciolosis is very rare (only 12 cases documented). In New Zealand, ''F. hepatica'' has never been detected in humans.<ref name=Mas-Coma99/>

===Animal fasciolosis===
Countries where fasciolosis in livestock was repeatedly reported:
*Europe: UK, Ireland, France, Portugal, Spain, Switzerland, Italy, Netherlands, Turkey, Germany, Poland
*Asia: Russia, Thailand, Iraq, Iran, China, Vietnam, India, Nepal, Japan, Korea, Philippines
*Africa: Kenya, Zimbabwe, Nigeria, Egypt, Gambia, Morocco
*Australia and the Oceania: Australia, New Zealand
*Americas:United States, Mexico, Cuba, Peru, Chile, Uruguay, Argentina, Jamaica, Brazil

On Sepember 8, 2007, Veterinary officials in South Cotabato, Philippines said that laboratory tests on samples from cows, carabaos, and horses in the province's 10 towns and lone city showed the level of infection at 89.5%, a sudden increase of positive cases among large livestock due to the erratic weather condition in the area. They mus be treated forthwih to prevent complications with Surra and Hemorrhagic Septicemia diseases. Surra already affected all barangays of the Surallah town.<ref>[http://www.gmanews.tv/story/59646/SunStar-Rise-in-animal-liver-fluke-cases-alarms-South-Cotabato GMA NEWS.TV, Rise in animal liver fluke cases alarms South Cotabato]</ref>

==Source of infection for humans and transmission==
Human ''F. hepatica'' infection is determined by the presence of the intermediate snail hosts, domestic herbivorous animals, climatic conditions and the dietary habits of man.<ref name=Chen/>  Sheep, goats and cattle are considered the predominant animal reservoirs. While other animals can be infected, they are usually not very important for human disease transmission. On the other hand, some authors have observed that Nasturtium officinale'' (common lamb’s lettuce), and ''Mentha viridis'' (spearmint) were reported as a source of human infections.<ref name=Mas-Coma99/> In the Northern Bolivian Altiplano, some authors suggested that several aquatic plants such as bero-bero (watercress), algas (algae), kjosco and tortora could act as a source of infection for humans.<ref>Bjorland, J., Bryan, R.T., Strauss, W., Hillyer, G.V., McAuley, J.B., 1995. An outbreak of acute fascioliasis among Aymara Indians in the Bolivian Altiplano. Clin. Infect. Dis. 21, 1228–1233.</ref> Because ''F. hepatica'' cercariae also encyst on water surface, humans can be infected by drinking of fresh untreated water containing metacercariae.<ref name=Chen/> In addition, an experimental study suggested that humans consuming raw liver dishes from fresh livers infected with juvenile flukes could become infected.<ref>Taira, N., Yoshifuji, H., Boray, J.C., 1997. Zoonotic potential of infection with ''Fasciola'' spp. by consumption of freshly prepared raw liver containing immature flukes. Int. J. Parasitol. 27, 775–779.</ref>

==Intermediate hosts==
280px|thumb|''Galba truncatula'' - the most common intermediate host of ''F. hepatica'' in Europe and South America
Intermediate hosts of ''F. hepatica'' are freshwater snails from family Lymnaeidae.<ref name=Torges99/><ref>{{cite book |last=Graczyk |first=TK |coauthors=Fried B |chapter=Development of ''Fasciola hepatica'' in the intermediate host.
|editor=Dalton, JP |title=Fasciolosis |publisher=CABI Pub |location=Wallingford, Oxon, UK |year=1999 |pages=31–46 |isbn=0-85199-260-9 }} (</ref> Snails from family Planorbidae act as an intermediate host of ''F. hepatica'' very occasionally.<ref name=Mas-Coma05/>

More reading in ''Fasciola hepatica''

==Pathogenesis==
The development of infection in definitive host is divided into two phases: '''the parenchymal (migratory) phase''' and '''the biliary phase'''.<ref name=Dubinsky>Dubinský, P., 1993. Trematódy a trematodózy. In: Jurášek, V., Dubinský, P. a kolektív, Veterinárna parazitológia. Príroda a.s., Bratislava, 158–187. (in Slovakian)</ref> The parenchymal phase begins when excysted juvenile flukes penetrate the intestinal wall. After the penetration of the intestine, flukes migrate within the abdominal cavity and penetrate the liver or other organs. ''F. hepatica'' has a strong predilection for the tissues of the liver.<ref name=Behm99>Behm, C.A., Sangster, N.C., 1999. Pathology, pathophysiology and clinical aspects. In: Dalton, J.P. (Ed.), Fasciolosis. CAB International Publishing, Wallingford, pp. 185–224.</ref> Occasionally, ectopic locations of flukes such as the lungs, diaphragm, intestinal wall, kidneys, and subcutaneous tissue can occur.<ref name=Boray69></ref><ref name=Chen/> During the migration of flukes, tissues are mechanically destroyed and inflammation appears around migratory tracks of flukes. The second phase (the biliary phase) begins when parasites enter the biliary ducts of the liver. In biliary ducts, flukes mature, feed on blood, and produce eggs. Hypertrophy of biliar ducts associated with obstruction of the lumen occurs as a result of tissue damage.