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Fasciola hepatica (view source)

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| Also known as:
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| '''Liver Fluke
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''Fasciola Hepatica'' is an hepatic parasite found in mainly in ruminants, namely cows, sheep and goats, but also known to affect horses and pigs.  It is found Worldwide, and within the UK, with its prevalence ever increasing.  It is responsible for a 10-15% production loss in each infected animal, as it affects meat, milk and wool production, so is of huge economic consequence.
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{{Taxobox
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|name              =''Fasciola hepatica
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|kingdom            =Animalia
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|phylum            =Platyhelminthes
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|class              =[[:Category:Trematodes|Trematoda]]
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|sub-class          =Digenea
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|order              =Echinostomida
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|super-family      =
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|family            =Fasciolidae
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|sub-family        =
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|genus              =Fasciola
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|species            =''Fasciola hepatica
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}}
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Also known as: '''''Liver Fluke
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''Fasiola Hepatica'' has a definitive ruminant mammalian host and an intermediate molluscian host. Within Europe the intermediate host is almost exclusively the snail 'Lymnaea truncatulata'. The snail habitat is crucial to the survival of the parasite, so wet conditions are favourable to the development and spread of Fasciola hepatica
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==Introduction==
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[[Image:Fasciola hepatica.jpg|400px|thumb|right|'''Fasciola hepatica (Copyright Adam Cuerden, Wikimedia Commons) ''']]
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''Fasciola Hepatica'' is an hepatic parasite of the class [[:Category:Trematodes|Trematoda]], found mainly in ruminants, namely cows, sheep and goats, but also known to affect horses, pigs, deer and man.  It is found Worldwide, and within the UK, with its prevalence ever increasing.  It is responsible for a 10-15% production loss in each infected animal, as it affects meat, milk and wool production, so is of huge economic consequence.
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{| {{prettytable}} 
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''Fasciola Hepatica'' has a definitive ruminant mammalian host and an intermediate molluscan host (indirect life cycle). Within Europe the intermediate host is almost exclusively the amphibious snail ''Galba truncatula'' (previously called ''Lymnaea truncatulata''). The snail habitat is crucial to the survival of the parasite, so wet conditions are favourable to the development and spread of ''Fasciola hepatica''.
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|+ '''Scientific Classification'''
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[[Image:Fasciola hepatica.jpg|400px|thumb|right|''Fasciola hepatica'' <br> Adam Cuerden 2007, Wikimedia Commons]]
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| Kingdom
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| Animalia
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|-
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| Phylum
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| Platyhelminthes
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|-
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| Class
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| Trematoda
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|-
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| Subclass
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| Digenea
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|-
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| Order
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| Echinostomida
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|-
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| Family
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| Fasciolidae
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|-
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| Genus
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| Fasciola
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|-
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| Species
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| '''F. Hepatica'''
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|}
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===Pathogenesis===
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==Life Cycle==
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The severity of the infection is mainly dependent on the number of metacercariae ingested. The Pathogenesis is often described as two-fold. The first stage occuring when the parasite migrates through the liver parenchyma, causing liver damage and haemorrhage.  The second phase occurs when the parasite is in the bile ducts, and damage is a result of the haematophagic activity of the adult flukes.
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Adult flukes in the bile ducts shed '''eggs''' directly into the bile, which then subsequently enter the intestine. Eggs are then passed out in the faeces of the mammalian host, where they develop and hatch releasing motile ciliated '''miracidia'''.  These require 9-10 days at optimal temperatures, of around 22-26 degrees. The miracidium have a short life and must locate a suitable snail, the intermediate host, within approximately 3 hours if they are to be effective and continue the life cycle.
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===Acute Fascioliasis===
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If successful, the miracidium will then develop into '''sporocysts''', then enter the '''redial stages''' to the final stages within the intermediate host, which is development into '''cercaria'''.  These cercaria are then released from the snail, and attach to surfaces such as the tips of grass.  Here they encyst and form '''metacercaria'''. This represents the infective stage of the lifecycle. 
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The acute disease is a less common type of Fasciola hepatica, and generally occurs 2-6 weeks after large ingestion of metacercariae.  The young liver flukes migrate through the liver parenchyma causing severe haemorrhaging, due to the damage to the [[Liver - Anatomy & Physiology|liver]] vasculature.  
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Development from miracidium into metacercariae takes around 6-7 weeks under favourable conditions, however, this period can be much longer in unfavourable conditions.
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This occurs in late autumn and winter, mainly between the months of August to October. Outbreaks of acute fascioliasis usually present as sudden deaths.  On examination infected animals are weak, with pale mucous membranes.  They may also have enlarged livers, and the liver surface may be cover with a fibrinous peritonitis, particularly evident on the ventral lobe. Tracts become filled with blood and degenerate hepatocytes later infiltrated with [[Eosinophils|eosinophils]], [[Lymphocytes|lymphocytes]] and replaced by fibrosis.
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Upon ingestion by the final or definitive host from the grass, metacercariae excyst to present as immature  flukes in the  small intestine. These then migrate  across the  peritoneal cavity over a period of roughly one week, and invade the liver. Larvae continue to migrate within the hepatic parenchyma, becoming more destructive as they grow to a length of up to one centimetre. The young liver flukes migrate through the liver for around 6-8 weeks before entering the bile ducts where they mature to adults and begin to produce eggs. They may also migrate into the gall bladder, where they reach full sexual maturity.
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The prepatent period of ''Fasciola hepatica'' is 10-12 weeks. In untreated sheep it may survive and continue to infect for many years. In cattle it is usually less than 1 year.
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==Identification==
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The egg is relatively large; around 140μm x 70μm.  It is oval shaped, with a thin outer shell, and is browny-yellow.
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The fully mature adult fluke is a dark brown colour, and around 3cm in length.
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==Snail biology==
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[[Image:Lymnaea truncatula.jpg|thumb|right|150px|''Lymnaea truncatula'' - Francisco Welter Schultes, Wikimedia Commons]]
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=== ''Lymnaea truncatula'' ===
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''Lympnea truncatula'' is around 5-10mm long. It has a distinctive brown-black shell, with 5-6 spirals present on the outer surface.  The first spiral is approximately half the total length of the snail.
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It feeds on green slime, and when this is present in abundance, they may multiply rapidly.
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Most die in the British winter, due to the harsh, cold conditions, but they may survive in milder winters.  Survivors will lay eggs in spring, which will hatch in June.
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[[Image:Fasciola hepatica - bile duct.jpg|300px|thumb|right|'''Fasciola hepatica (Copyright Flukeman, Wikimedia Commons) ''']]
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===Habitats===
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''Lymnaea'' are found predominantly in muddy areas, but do not survive well in highly acidic soils.  Habitats may be permanent; seen in dry summers or temporary; found in wet summers.
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===Subactute Fascioliasis===
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===Epidemiology===
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This is caused by ingestion of metacercariae over a longer period of time.  Some may have migrated to the bile ducts, causing [[cholangitis]], whilst other metacercariae are migrating through the liver causing lesions similar to those present in acute fascioliasis. The infected host may present with severe haemorrhagic anaemia, with [[hypoalbuminaemia]], rapid loss of body condition, reduced appetite, pale mucous membranes, and submandibular oedema may also be present. On post-mortem, an enlarged liver is common and haemorrhagic tracts are usually visible on the liver surface. If left untreated, it is often fatal.  This form of fascioliasis occurs around 6-10 weeks after ingestion of the metacercariae by the host, and like acute fascioliasis occurs in late autumn and winter.
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Wet summers increase both the number of snail habitats and the hatching of fluke eggs, leading to many infected snails. These in turn shed many cercariae, which form a high density of metacercariae on herbage to increase the risk of fasciolosis. Conversely, in dry summers, fewer fluke eggs hatch and snails are restricted to their permanent habitats. Fewer snails become infected and cercariae and metacercariae numbers are low and confined to the areas where snails can survive. The risk of fasciolosis is therefore reduced.
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===Chronic Fascioliasis===
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In temperate areas, there are two superimposed epidemiological cycles, known as the summer and winter infections of the snail. On mainland Britain, the summer cycle predominates as a high proportion of snails perish during the winter, but very occasionally, weather sequences allow the winter cycle to affect the pattern of disease. On the west coast of Ireland, the winter cycle of events determines the timing of clinical outbreaks.
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This is usually seen in late winter, early spring and is currently the most common fascoloiasis seen. It occurs around 4-5 months after ingestion of the metacercariae.  Hypochromic and macrocytic anaemia and hypoalbuminaemia are common, as the adult flukes are capable of sucking up to 0.5ml of blood each day. In heavy infections, this can prove to be a severe loss.  
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Infected animals may present with progressive loss of body condtion, reduced appeptite, which along with hypoalbuminaemia can result in an gaunt animal. Other common signs include pale mucous membranes, and submandibular oedema, more commonly known as 'bottle jaw.'  On biopsy the liver will have an irregular shape, distorted shape with areas of fibrous tissue replacing the cells damaged by the migrating flukes. The bile ducts appear dilated, and dark, and it is often possible to express numerous numbers of adult flukes from within the ducts. Pathology is similar in both sheep and cattle, expect in cattle you may see calcification of the bile ducts, and enlargement of the gall bladder. The calcified bile ducts are often seen protruding from the liver surface, which is known as 'pipe stem liver.'
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==== Summer infection of the snail ====
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The fluke eggs passed in spring will hatch in June. This coincides with the hatching of the snail. The miracidia will then infect the newly hatched snails, mature and then multiply within the snail hepatopancreas during the summer months.
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===Diagnosis===
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The cercariae are shed from late August onwards. The metacercariae develop and are ingested by a host; the sheep for example.  The immature flukes then migrate through the liver, causing acute disease between the months of September and November, or chronic disease from January onwards.
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This is performed primarily on the clinical findings, seasonal occurance, as well as a previous history of fasciolosis on the farm.  These along with post-mortem form the basis for diagnosis of Fasciola hepatica. In practice, diagnosis of ovine fasciolosis is often more straightforward than bovine fasciolosis.
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Examination of faeces for liver fluke eggs is also useful, and may be complemented by laboratory tests.  Firstly the measurement of Glutamate dehydrogenase (GLDH) is used.  This is an enzyme released by damaged hepatic cells, and levels become elevated within the first few weeks of infection. Another test commonly used is measuring the glutamyl transpeptidase (GGT), and this indicates damage to the epithelial cells of the bile ducts, and is seen later in the cycle, and maintained for a longer duration.
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====Winter infection of the snail====
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In this case the fluke eggs are passed in the late summmer, which then infect the snails.  Environmental conditions play a vital role in the success of the fluke development.  Temperatures below 10 degrees will see the development being haltered, and the flukes will remain trapped in the hibernating snails throughout the winter.  Development will then resume when temperatures rise above 10 degrees. The cercariae are then shed from July, and disease may be seen from August onwards.
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An [[ELISA]] can also be used in the detection process. It identifies antibodies against flukes in the serum and milk samples, and is deemd to be extremely reliable in this case.
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==Pathogenesis==
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===Treatment===
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The severity of the infection, [[Fasciolosis]], is mainly dependent on the number of metacercariae ingested.  The pathogenesis is often described as two-fold. The first stage occurring when the parasite migrates through the liver parenchyma, causing liver damage and haemorrhage.  The second phase occurs when the parasite is in the bile ducts, and damage is a result of the haematophagic activity of the adult flukes.
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If the fuke is present treat with triclabendazole, which is effective against all stages of Fasciola hepatica.  Treatment should be applied in September/October and again in January, if faecal egg count is still postitive. One may also treat against adult only stages in May/June, preventing any future pasture contamination. However, do not use the same treatment in September/October as used in May/June, as resistance to drugs is becoming a real problem within the UK due to overuse. If it has been a particularly wet season, it may be necessary to treat again, as Fasciola hepatica becomes more prevalent under such conditions.
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{{Learning
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|literature search = [http://www.cabdirect.org/search.html?rowId=1&options1=AND&q1=%22Fasciola+hepatica%22&occuring1=title&rowId=2&options2=AND&q2=&occuring2=freetext&rowId=3&options3=AND&q3=&occuring3=freetext&publishedstart=2000&publishedend=yyyy&calendarInput=yyyy-mm-dd&la=any&it=any&show=all&x=46&y=7 ''Fasciola hepatica'' publications since 2000]
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|flashcards = [[Trematodes_Flashcards|Trematodes Flashcards]]
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}}
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Isolation and treatment of all new animals entering from another farm has also be shown to be effective.  Other control measures include fencing off wet areas, and increasing soil drainage.
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==References==
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Taylor, M.A, Coop, R.L., Wall,R.L. (2007) '''Veterinary Parasitology''' ''Blackwell Publishing''
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G.L. Pritchard et al., Emergence of fasciolosis in cattle in East Anglia, ''The Veterinary Record'', November 5, 2005.
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{{review}}
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==Webinars==
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<rss max="10" highlight="none">https://www.thewebinarvet.com/parasitology/webinars/feed</rss>
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[[Category:Trematodes]]
 
[[Category:Liver Trematodes]]
 
[[Category:Liver Trematodes]]
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[[Category:Cattle Parasites]][[Category:Sheep Parasites]][[Category:Horse Parasites]][[Category:Pig Parasites]][[Category:Goat Parasites]]
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[[Category:To_Do_-_Max]]
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[[Category:Expert_Review - Parasites]]
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[[Category:To_Do_-_Review]]
 
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