''Fascioloides magna'', also known as giant liver fluke, large American liver fluke or deer fluke, is

trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive h ...

parasite that occurs in wild and domestic

ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...

s in North America and Europe. Adult flukes occur in the liver of the definitive host and feed on blood. Mature flukes measure in length × in width, and have an oval dorso-ventrally flattened body with oral and

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

sucker Sucker may refer to: General use * Lollipop or sucker, a type of confection * Sucker (slang), a slang term for a very gullible person * Hard candy ** Cough drop ** Mint (candy) Biology * Sucker (botany), a term for a shoot that arises undergro ...

. The flukes are reddish-brown in colour and are covered by tegument. As with other

digenea Digenea (Gr. ''Dis'' – double, ''Genos'' – race) is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms (known as ''flukes'') with a syncytial tegument and, usually, two suckers, one ventral and one oral. ...

s, the life cycle includes intramolluscan phase in snails.Erhardová-Kotrlá, B., 1971. The occurrence of ''Fascioloides magna'' (Bassi, 1875) in Czechoslovakia. Academia, Prague, 155 pp.Pybus, M.J., 2001. Liver flukes. In: Samuel, W.M., Pybus, M.J., Kocan, A.A. (eds.), Parasitic diseases in wild mammals, Iowa State Press, Iowa City, pp 121–149. The parasite is currently distributed in wild ruminants in North America and Europe, including Austria, Canada, the Czech Republic, Croatia, Germany, Hungary, Italy, Poland, Serbia, Slovakia, and the United States.

History

''Fascioloides magna'' is essentially of North American origin but the parasite was introduced into Europe with imported game animals at the second half of the 19th century. In spite of being native to North America the fluke was first described in

Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...

. In 1875, Bassi observed massive deaths of red deer in the Royal Park (now La Mandria Regional Park) near

Torino Turin ( , Piedmontese: ; it, Torino ) is a city and an important business and cultural centre in Northern Italy. It is the capital city of Piedmont and of the Metropolitan City of Turin, and was the first Italian capital from 1861 to 1865. T ...

, Italy. The signs were similar to well known

fasciolosis Fasciolosis 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). ...

in sheep. He named it ''Distomum magnum''. The author believed that the parasite was introduced into the park in wapiti imported from the United States in 1865. Most workers did not accept Bassi’s species because of his poor description. From 1882 to 1892, the fluke was recorded from different areas of the United States and described separately by many authors. Later, Stiles (1894) pointed out that the American findings are identical with species described previously by Bassi. Stiles made a complete morphological description of the adult fluke and named it ''Fasciola magna'' (Bassi 1875) Stiles 1894. In 1917, Ward showed that owing to the lack of the distinct anterior cone and the fact that

vitellaria ''Vitellaria paradoxa'' (formerly ''Butyrospermum parkii''), commonly known as shea tree, shi tree (), or vitellaria, is a tree of the family Sapotaceae. It is the only species in the genus ''Vitellaria'',intestinal branches, he established a new

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

''Fascioloides'' and rename it to ''Fascioloides magna'' (Bassi 1875) Ward 1917. In 1895, Stiles suggested that the life cycle of the fluke is very similar to '' Fasciola hepatica'', i.e. it includes an aquatic snail as an intermediate host. He gave a comparative description of the egg and miracidium of the fluke. However, first reported intermediate hosts of ''F. magna'' were not published until 1930’s. The complete life cycle of ''F. magna'', including a description of all the larval stages, was described by Swales (1935) in Canada.

Life cycle

The life cycle of ''F. magna'' is relatively complex and is similar to the development of the related fluke, ''F. hepatica''. A detailed account of the ''F. magna'' life cycle was given by Swales (1935), Erhardová-Kotrlá (1971), and reviewed by Pybus (2001).Adult flukes occur in pairs or groups within a fibrous capsule in the liver parenchyma of the definitive host. Mature flukes release eggs which are collected in the cavity of the capsule. The capsule contains a great mass of eggs and has duct connections to bile ducts. The eggs are passed together with bile into the bile collecting system, enter the small intestine, and leave the definitive host along with the faeces. The eggs which are passed out in the faeces into the environment are undeveloped and undergo embryonation outside the host. Several physical-chemical factors, especially temperature,

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity dep ...

and

oxygen tension Blood gas tension refers to the partial pressure of gases in blood. There are several significant purposes for measuring gas tension. The most common gas tensions measured are oxygen tension (PxO2), carbon dioxide tension (PxCO2) and carbon monox ...

, are known to influence embryonation. During the embryonation of the egg, a larva called a miracidium develops from germinal cells. Fully developed miracidium releases the operculum of the egg using several proteases. The embryonation period varies from 27 to 44 days in natural conditions. Ciliated miracidia hatch in water and actively seek suitable intermediate hosts that are freshwater snails from family

Lymnaeidae Lymnaeidae, common name the pond snails, is a taxonomic family of small to large air-breathing freshwater snails, aquatic pulmonate gastropod mollusks, that belong to the clade Hygrophila. Lymnaeidae is the only family within the superf ...

. After attaching to a suitable snail host, the miracidium penetrates into the snail body. After shedding its ciliated cell layer it is called a sporocyst. The sporocysts are found in the foot, the snail body, digestive glands, reproductive organs, and in the pulmonary sac of the snail. The sporocysts contain germinal cells that give rise to 1–6 mother rediae (a trematode larval form with an oral sucker). Developed mother rediae are released from the sporocyst and migrate into digestive glands, renal organ, reproductive organs, and pulmonary sac of the snail body. Each mother redia can asexually produce up to 10 daughter rediae. However, only 3 to 6 daughter rediae complete their development and leave the mother rediae. In turn, each daughter redia may produce 1–6

cercariae Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two suckers: one ventral and the other oral. Trematodes are covered by a tegument, that protects the organism from the environment by providing secr ...

in experimentally infected snails and 16–22 cercariae under natural conditions. Cercariae emerge from the rediae and mature usually in digestive glands of the snail. Mature cercarie spontaneously emerge from the snail host and swim actively in water for up to two hours before encysting on vegetation. After encystment the flukes are called metacercariae. Development within the snail takes 40 to 69 days depending upon the temperature and the species of snail. The definitive host ingests vegetation containing the metacercariae. In the stomach and the intestine, the metacercariae are stimulated to emerge from the cyst ( excystation). Newly excysted juvenile flukes penetrate the wall of the intestine and migrate in the abdominal cavity. Juvenile flukes penetrate the

Glisson's capsule The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it is ...

of the liver and continue migrating in the liver tissue. Rarely juvenile flukes penetrate other organs, such as lungs or kidneys. In these organs, however, flukes do not survive and not attain maturity. In the liver, flukes migrate within the parenchyma to search another fluke. If the fluke meet another one, they stop moving, and the fibrous capsule is formed around them. In the capsule, the parasite completes its development and starts egg-laying. Prepatent period varies 3–7 months and is dependent on host species. Adult ''F. magna'' can survive in the liver of the host up to 7 years.

Distribution

Currently, ''F. magna'' occurs only in North America and Europe where suitable

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

exists and susceptible intermediate hosts are found. However, sporadic works reported unique appearance of the fluke in other continents. ''F. magna'' was found in imported animals in South Africa, Australia and Cuba. In all cases, infected animals (brahman heifer, ox, and elk, respectively) were imported from the United States or Canada.Špakulová, M., Rajský, D., Sokol, J., Vodňanský, M., 2003. Giant liver fluke (''Fascioloides magna''), an important liver parasite of ruminants. Parpress, Bratislava, 61 pp.

North America

During the 20th century, ''F. magna'' was reported in these American states: Arkansas, California, Colorado, Illinois, Iowa, Kansas, Louisiana, Michigan, Minnesota, Montana, New York, Oklahoma, Oregon, South Carolina, Texas, Washington, and Wisconsin. Areas of New England are not areas normally inhabited by ''F. magna'', but the fluke has been reported in this region. In Canada, the fluke was reported in Alberta, British Columbia, Ontario, and Quebec. Currently, ''F. magna'' is enzootic in five major areas: (1) the

Great Lakes The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lakes ...

region; (2) the Gulf coast, lower Mississippi, and southern Atlantic seaboard; (3) northern Pacific coast; (4) the Rocky Mountain trench; and (5) northern Quebec and Labrador. However, within these broad ranges, actual presence of giant liver flukes varies from locally abundant to locally absent.

Europe

''Fascioloides magna'' was first reported by Bassi in Torino, Italy. In spite of Bassi's work, no other data concerning the occurrence of ''F. magna'' in Europe were reported until the 1930s. In the

Czech Czech may refer to: * Anything from or related to the Czech Republic, a country in Europe ** Czech language ** Czechs, the people of the area ** Czech culture ** Czech cuisine * One of three mythical brothers, Lech, Czech, and Rus' Places * Czech, ...

territory, Ullrich reported the first appearance of ''F. magna'' in fallow deer as late as 1930.Ullrich, K., 1930. Über das Vorkommen von seltenen oder wenig bekannten Parasiten der Säugetiere und Vögel in Böhmen und Mähren. Prager Archiv Tiermedicine 10, A (1/2), 19–43. At the same time, Salomon (1932) diagnosed the fluke in one hunted

red deer The red deer (''Cervus elaphus'') is one of the largest deer species. A male red deer is called a stag or hart, and a female is called a hind. The red deer inhabits most of Europe, the Caucasus Mountains region, Anatolia, Iran, and parts of ...

near

Görlitz Görlitz (; pl, Zgorzelec, hsb, Zhorjelc, cz, Zhořelec, East Lusatian dialect: ''Gerlz'', ''Gerltz'', ''Gerltsch'') is a town in the German state of Saxony. It is located on the Lusatian Neisse River, and is the largest town in Upper Lus ...

(Saxony) in Germany. Other isolated findings of the fluke were recorded in Italy and Poland. From 1948 to 1961, sporadic occurrence of the parasite in red deer (''Cervus elaphus''),

fallow deer ''Dama'' is a genus of deer in the subfamily Cervinae, commonly referred to as fallow deer. Name The name fallow is derived from the deer's pale brown colour. The Latin word ''dāma'' or ''damma'', used for roe deer, gazelles, and antelopes ...

(''Dama dama'') and

roe deer The roe deer (''Capreolus capreolus''), also known as the roe, western roe deer, or European roe, is a species of deer. The male of the species is sometimes referred to as a roebuck. The roe is a small deer, reddish and grey-brown, and well-adapt ...

(''Capreolus capreolus'') were reported by several authors in former

Czechoslovakia , rue, Чеськословеньско, , yi, טשעכאסלאוואקיי, , common_name = Czechoslovakia , life_span = 1918–19391945–1992 , p1 = Austria-Hungary , image_p1 ...

. However, all reports were published on the basis of incident discoveries in hunted deer and no massive infections were documented. In 1960s, a number of ''F. magna'' outbreaks in

cervid Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindee ...

s were reported in some areas of former Czechoslovakia. The prevalence of infection varied from 70 to 80% in red deer and maximum parasite burden was 144 worms. In addition, sudden deaths were documented in free or game ranging deer. The highest mortality was reported in free ranging roe deer in Písek County in the

South Bohemia The South Bohemian Region ( cs, Jihočeský kraj; , ) is an administrative unit (''kraj'') of the Czech Republic, located mostly in the southern part of its historical land of Bohemia, with a small part in southwestern Moravia. The western part ...

of former

Czechoslovakia , rue, Чеськословеньско, , yi, טשעכאסלאוואקיי, , common_name = Czechoslovakia , life_span = 1918–19391945–1992 , p1 = Austria-Hungary , image_p1 ...

. In the same region, moreover, the parasite was found in livers of slaughtered cattle.Záhoř, Z., 1965. Výskyt velké motolice (''Fascioloides magna'' Bassi, 1875) u srnčí zvěře. Veterinářství 15, 322–324. Erhardová-Kotrlá (1971) confirmed red deer, fallow deer and roe deer as main definitive hosts of ''F. magna'' in Europe. In the 1960s, ''F. magna'' was enzootic in former Czechoslovakia in following four major areas: (1)

České Budějovice České Budějovice (; german: Budweis ) is a city in the South Bohemian Region of the Czech Republic. It has about 93,000 inhabitants. It is located in the valley of the Vltava River, at its confluence with the Malše. České Budějovice is t ...

and

Třeboň Třeboň (; german: Wittingau) is a spa town in Jindřichův Hradec District in the South Bohemian Region of the Czech Republic. It has about 8,100 inhabitants. The town centre with the castle complex is well preserved and is protected by law as an ...

county, including Nové Hrady Mountains; (2) the area along the

Vltava Vltava ( , ; german: Moldau ) is the longest river in the Czech Republic, running southeast along the Bohemian Forest and then north across Bohemia, through Český Krumlov, České Budějovice and Prague, and finally merging with the Labe at ...

River on the Vltava-Týn hills near Hluboká and

Bechyně Bechyně (; german: Bechin, Beching or ''Bechingen'') is a town in Tábor District in the South Bohemian Region of the Czech Republic. It has about 4,900 inhabitants. The historic town centre is well preserved and is protected by law as an urba ...

; (3)

Písek Písek (; german: Pisek) is a town in the South Bohemian Region of the Czech Republic. It has about 30,000 inhabitants. The town centre is well preserved and is protected by law as an urban monument zone. Písek is colloquially called "''South ...

and Milevsko county; (4) the

Brdy Brdy is a range of hills in the Czech Republic, forming a long massif stretching for c. 60 km southwest from Prague. The northern section of the Brdy is called "Hřebeny" and features one narrow ridge (highest elevation Písek - 690 m). The m ...

mountains and the Hřebeny mountains. In following years, ''F. magna'' was only reported from these areas. Recently, geographical distribution of ''F. magna'' in cervids was determined in the

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

. The giant liver fluke was confirmed in the same areas as reported in the 1960s. However, seven new endemic areas of ''F. magna'' were discovered suggesting that the parasite is spreading in the Czech Republic. Moreover, the appearance of ''F. magna'' in the

Šumava The Bohemian Forest, known in Czech as Šumava () and in German as Böhmerwald, is a low mountain range in Central Europe. Geographically, the mountains extend from Plzeň Region and South Bohemia in the Czech Republic to Austria and Bavaria ...

Mountains has epizootiological importance due to possibility of spread of the parasite into the German territory (

Bavaria Bavaria ( ; ), officially the Free State of Bavaria (german: Freistaat Bayern, link=no ), is a state in the south-east of Germany. With an area of , Bavaria is the largest German state by land area, comprising roughly a fifth of the total l ...

).Novobilský, A., Horáčková, E., Hirtová, L., Modrý, D., Koudela, B., 2007. The giant liver fluke ''Fascioloides magna'' (Bassi, 1875) in cervids in the Czech Republic and potential of its spreading to Germany. Parasitology Research 100, 549–553. During the last few years, a new European enzootic area has established in the

Danube The Danube ( ; ) is a river that was once a long-standing frontier of the Roman Empire and today connects 10 European countries, running through their territories or being a border. Originating in Germany, the Danube flows southeast for , pa ...

watershed in Central Europe. In 1988, ''F. magna'' was isolated from a 3-year old red deer female found dead near the

Gabčíkovo Gabčíkovo ( hu, Bős, ) is a town and municipality in the Dunajská Streda District, in the Trnava Region of southwestern Slovakia. It has 5,232 inhabitants of whom approximately 80% are Hungarians. After the Communist takeover of Czechoslovak ...

water plant at the Danube River in Slovakia. The parasite has spread through whole Slovakian Danube watershed. Soon after the Slovakian first report, ''F. magna'' was found in red deer in Hungarian parts of Danubian floodplain forests. The prevalence reported by the same authors was up to 90%. ''F. magna'' infection of cervids is a considerable problem in northern part of Hungary (

Szigetköz The Szigetköz (literally "island alley"; german: Kleine Schüttinsel, lit=Little Schütt Island; sk, Malý Žitný ostrov, lit=Little Rye Island) is an island on the Danube in Western Hungary, part of the Little Hungarian Plain. It is the larg ...

) and the southern Danubian territory in the

Gemenc Gemenc is a unique forest that is found between Szekszárd and Baja, in Hungary. This is the only remaining tidal area of the Danube in Hungary. The wood's fauna include stags, boars, storks, grey herons, gyrfalcons, white-tailed eagles, and kit ...

area. Since the autumn of 2000, ''F. magna'' has been found in Austrian territory, east of

Vienna en, Viennese , iso_code = AT-9 , registration_plate = W , postal_code_type = Postal code , postal_code = , timezone = CET , utc_offset = +1 , timezone_DST ...

. In years 2000–2001, the prevalence of the giant liver fluke in red deer in Austrian parts of Danube (east of Vienna) was 66.7%.Ursprung, J., Joachim, A., Prosl, H., 2006. Epidemiology and control of the giant liver fluke, ''Fascioloides magna'', in a population of wild ungulates in the Danubian wetlands east of Vienna. Berliner und Müncher Tiermedicine Woch 119, 316–323. Appearance of American liver fluke was reported in Croatia in January 2000. The prevalence of fascioloidosis among red deer in Hungary was 21,1–60,7 % between 1998–2005. During the necropsy of 459 deer livers (using Egri's method) the number of flukes per host ranged from 1 to 138 in the same period.Giczi E, Egri B, 2006. Quantitative parasitologische Untersuchungsergebnisse zum Vorkommen von Fascioloides magna (Bassi, 1875) bei Rothirschen im Nordwesten von Ungarn (1998–2005). Tierarztl. Umschau 61, 660–666. Regarding the origin of ''F. magna'' enzootic area in the Danube River watershed, it is essential to point out that cervids were not introduced into these localities, neither recently nor in the past. Origin of the ''F. magna'' population in Danubian floodplain forests in Central Europe remains therefore unclear.

Definitive hosts

Natural infections of ''F. magna'' occur primarily in cervids and bovids. Although many species are susceptible to infection, only a few cervid species contribute significantly to maintaining populations of the fluke. In North America, the common definitive hosts of the giant liver fluke are wapiti (''Cervus elaphus canadensis''),

white-tailed deer The white-tailed deer (''Odocoileus virginianus''), also known as the whitetail or Virginia deer, is a medium-sized deer native to North America, Central America, and South America as far south as Peru and Bolivia. It has also been introduced t ...

(''Odocoileus virginianus'') and

caribou Reindeer (in North American English, known as caribou if wild and ''reindeer'' if domesticated) are deer in the genus ''Rangifer''. For the last few decades, reindeer were assigned to one species, ''Rangifer tarandus'', with about 10 subspe ...

(''Rangifer tarandus''). In Europe, ''F. magna'' occurs commonly in red deer (''Cervus elaphus''), fallow deer (''Dama dama'') and roe deer (''Capreolus capreolus''). Domestic ruminants are also susceptible to natural infection with ''F. magna''. However, the infection is not patent, and domestic ruminants do not contribute to the propagation of the parasite in the environment. In North America, the giant liver fluke is commonly found in cattle, sheep and goats in areas where ''F. magna'' is enzootic in deer. In contrast, ''F. magna'' occurs rarely in domestic ruminants in Europe. The list of all natural definitive hosts of ''F. magna'' is presented in Table. Humans are not known to be a definitive host. The only indigenous primary definitive host of ''F. magna'' is white-tailed deer. This species has been parasitized by the fluke for the longest time in historical context. Wapiti and caribou are of Eurasian origin and entered North America during the

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

epoch, and overlapped with white-tailed deer in some parts of North America. They might have encountered ''F. magna'' in these shared biotopes.

(1) Definitive hosts

Definitive hosts are primarily New World and some Old World cervids. In definitive hosts, flukes are encapsulated in thin-walled fibrous capsules communicating to the bile system. The eggs are passed through the bile system, enter the small intestine, and leave the host with faeces. Therefore, the infection is patent. The capsules are a result of the defence response of the host to the parasite and are pathognomonic for ''F. magna'' infection. They contain two to five flukes, greyish-black fluid with eggs and cell detritus. ''F. magna'' infections in definitive hosts are usually subclinical. However, massive deaths caused by the fluke in red-, fallow- and roe deer were reported. Lethargy, depression, weight loss and decreased quality of antlers can occur sporadically. In addition, nervous symptoms were observed very rarely. In the first case, urging motion followed by apathy was reported in one experimentally infected fallow deer.Erhardová-Kotrlá, B., Blažek, K., 1970. Artificial infestation caused by the fluke ''Fascioloides magna''. Acta Veterinaria Brno 39, 287–295. Authors suggested that these symptoms were associated with hepatocerebral syndrome. Other author has observed partial paralysis in naturally infected wapiti caused by migrating juvenile flukes in the spinal cord. Biochemical and haematological profiles are little investigated in definitive hosts. A decrease of

haemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

, elevation of γ-globulins, and increase of

eosinophil Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells (WBCs) and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. A ...

s in serum was observed in experimentally infected white-tailed deer.

(2) Dead-end hosts

Dead-end hosts are represented by large bovids, suids, llamas, horses and some Old World cervids. Infections in dead-end hosts are characterized by excessive fibrosis, thick-walled encapsulation of flukes within hepatic parenchyma, and black pigmentation of various tissues. Both afferent and efferent bile ducts are totally occluded and are marked by tracts of fibrous tissue. The eggs can not be passed into the bile system, and, therefore, the infection is not patent. In addition, flukes rarely mature in dead-end hosts probably due to strong immune response. Nevertheless, appearance of ''F. magna'' eggs in the faeces of a single experimentally infected calf has been documented. Rarely have the pathophysiology or clinical symptoms in dead-end hosts have been studied. In cattle, significant elevations of eosinophil counts in periphery blood but only slight increases of AST and GGT have been observed.Conboy, G.A., Stromberg, B.E., 1991. Hematology and clinical pathology of experimental ''Fascioloides magna'' infection in cattle and guinea pigs. Veterinary Parasitology 40, 241–255. While American authors have not observed any clinical symptoms in cattle, anorexia and weight loss were recorded in naturally infected bulls in the former Czechoslovakia.

(3) Aberrant hosts

Aberrant hosts of ''F. magna'' are sheep and goats. However, the course of infection is similar in guinea pigs, rabbits, bighorn sheep (''Ovis canadensis'') and chamois (''Rupicapra rupicapra'') that were infected experimentally. Infections in aberrant hosts are characterized by excessive wandering of juvenile flukes and death of the host. Aberrant hosts die usually within 6 months post-infection and the death is associated with acute peritonitis or extensive

haemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, v ...

caused by migrating flukes.Stromberg, B.E., Conboy, G.A., Hayden, D.W., Schlotthauer, J.C., 1985. Pathophysiologic effects of experimentally induced ''Fascioloides magna'' infection in sheep.

American Journal of Veterinary Research American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

46, 1637–1641. In aberrant hosts, flukes do not mature and migrate until the host dies. Occasionally, a few flukes mature and eggs can be found in the faeces.Novobilský, A., Kašný, M., Mikeš, L., Kovařčík, K., Koudela, B., 2007. Humoral immune responses during experimental infection with ''Fascioloides magna'' and ''Fasciola hepatica'' in goats and comparison of their excretory/secretory products. Parasitology Research 101, 357–364. Hepatic lesions in aberrant hosts generally include firm

adhesion Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another). The forces that cause adhesion and cohesion can ...

s of the liver to the

diaphragm Diaphragm may refer to: Anatomy * Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen * Pelvic diaphragm or pelvic floor, a pelvic structure * Urogenital diaphragm or triangular ligament, a pelvic structure Other * Diap ...

, black pigmentation,

hematoma A hematoma, also spelled haematoma, or blood suffusion is a localized bleeding outside of blood vessels, due to either disease or trauma including injury or surgery and may involve blood continuing to seep from broken capillaries. A hematoma is ...

s, necroses, and haemorrhagic tracts in which juvenile flukes are located. While a lack of fibrous capsules within hepatic parenchyma has been reported by several authors, flukes in fibrous capsules have also been documented in sheep. However, the wall of the capsule is different from those found in cervids and large bovids. The dominant feature is a diffuse fibrosis throughout the liver and haemorrhagic migratory tracts containing erythrocytes, black pigment, and cell detritus. The liver lesions are infiltrated by eosinophils, plasma cells, and pigment-laden macrophages. Sheep and goats die acutely without any previous clinical signs. Only elevation of eosinophils and slight increase of γ-globulins were observed in experimentally infected sheep. Recently, several changes in biochemical and haematological profile have been documented in experimentally infected goats. The significant increase of GLDH (

glutamate dehydrogenase Glutamate dehydrogenase (GLDH, GDH) is an enzyme observed in both prokaryotes and eukaryotic mitochondria. The aforementioned reaction also yields ammonia, which in eukaryotes is canonically processed as a substrate in the urea cycle. Typical ...

) was recorded from 14 weeks after infection in goats experimentally infected with ''F. magna''.

Intermediate hosts

Since the presence of an intermediate host is essential to the completion of the life cycle, snails occupy the important role in the epidemiology of ''F. magna''. The intermediate hosts of the giant liver fluke belong to the family

. In North America, a total of 10 lymnaeid snails were reported as intermediate hosts of ''F. magna''. 6 of 10 North American snail species were found naturally infected and the other four were infected only under experimental conditions. In addition, the Australian species ''Austropeplea'' (''Lymnaea'') ''tomentosa'' was exposed to the North American isolate of ''F. magna'' and the parasite was able to complete its development. The most common North American natural snail hosts of the fluke are ''Fossaria'' (''Galba'') ''modicella'', ''Stagnicola'' (''Lymnaea'') ''caperata'' and ''Fossaria'' (''Galba'') ''bulimoides techella''. In Europe, an intermediate host had not been known until 1960’s. At the beginning, Ślusarski assumed that '' Lymnaea stagnalis'' could act as an intermediate host of ''F. magna'' in Europe. His assumption, however, has been neither confirmed by positive findings in the field nor by experimental infection. In 1961, Dr. Erhardová described the life cycle of ''F. magna'' based on observations of experimentally and naturally infected snails. She confirmed that ''

Galba truncatula ''Galba truncatula'' is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Lymnaeidae, the pond snails.Neubauer, Thomas A. (2014). Galba (Galba) truncatula (Müller, 1774). Accessed through: World R ...

'' is an intermediate host of the giant liver fluke in Europe. In later works, the author studied another lymnaeid species in the former Czechoslovakia. However, ''G. truncatula'' was repeatedly confirmed as the only snail host of ''F. magna''. In 1979, Chroustová reported successful experimental infection of ''Stagnicola'' (''Lymnaea'') ''palustris'' with ''F. magna''. She considered that this species might serve as an intermediate host of the fluke in the environment. Nevertheless, no naturally infected snails were found.Chroustová, E., 1979. Experimental infection of ''Lymnaea palustris'' snails with ''Fascioloides magna''. Veterinary Parasitology 5, 57–64. Recent studies indicate that another lymnaeid snail, ''

Radix peregra ''Peregriana peregra'' is a species of air-breathing freshwater snail, an aquatic pulmonate gastropod in the family Lymnaeidae, the pond snails. Distribution and habitat This small pond snail is found in Europe, Newfoundland and northern Asia. ...

'', may be also involved in the transmission of ''F. magna'' in Europe. This opinion is supported by successful experimental infection of ''R. peregra'' in the lab as well as by findings of naturally infected ''R. peregra'' in the environmentFaltýnková, A., Horáčková, E., Hirtová, L., Novobilský, A., Modrý, D., Scholz, T., 2006. Is ''Radix peregra'' a new intermediate host of ''Fascioloides magna'' (Trematoda) in Europe? Field and experimental evidence. Acta Parasitologica 51, 87–90. These findings suggested that the intermediate host spectrum of ''F. magna'' should be, similarly to North America, diverse in Europe. The list of intermediate hosts of ''F. magna'' is presented in following table. (*) Snails originated from Australia infected with United States isolate of ''F. magna''
(**) Snails originated from France infected with Czech isolate of ''F. magna''

Clinical signs, pathology and pathophysiology

According to several American authors, three types of definitive host exist: * (1) definitive hosts * (2) dead-end hosts * (3) aberrant hosts Pathology of ''F. magna'' infection varies according to host type but some features are shared by all three types. Primary lesions usually occur in the liver and are associated with mechanical damage due to migrating juvenile flukes or fibrous encapsulation of sedentary adult flukes. The most common feature of ''F. magna'' infection is black pigmentation in abdominal or thoracic organs, especially in the liver. The hematin pigment is produced by flukes as a byproduct of feeding on blood. Pigment within tissues is a result of migrating of juvenile flukes and it accumulates within hepatic cells without resorption. ''F. magna'' has also been associated with Red Water disease in bovine. ''F. magna'' causes liver damage, which allows the bacteria ''Clostridium haemolyticum'' to cause secondary infection in hepatic tissue. The infection will decrease the livers function, and the host's urine will become red, hence the name "Red Water" disease.

Diagnosis

While the eggs of ''F. magna'' resemble those of '' F. hepatica'', this similarity is of limited use; eggs usually are not passed in cattle and sheep. Recovery of the parasites at necropsy, as well as proper identification of ''F. hepatica'' or ''F. gigantica'' is necessary for definite diagnosis. When domestic ruminants and deer share the same grazing areas, the presence of disease due to ''F. magna'' should be kept in mind. Mixed infections with ''F. hepatica'' occur in cattle.

Control of ''F. magna'' and prevention

For control of fascioloidosis in wild ruminants, successful application of anthelminthics in feed is necessary. The drug has to have flavour and smell that do not prevent animals from eating medicated feed. In addition, there should adequate therapeutic scope, i.e. span between therapeutic and minimal toxic dose. Therefore, only some of anthelminthics that are efficient in domestic ruminants have been tested in wild ruminants infected with ''F. magna''. Several drugs, namely oxyclozanide,

rafoxanide Rafoxanide is a salicylanilide used as an anthelmintic. It is most commonly used in ruminant animals to treat adult liver flukes of the species ''Fasciola hepatica'' and ''Fasciola gigantica ''Fasciola gigantica'' is a parasitic flatworm of th ...

albendazole Albendazole (also known as albendazolum) is a broad-spectrum anthelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, ho ...

, diamphenetide, closantel, clorsulon, and

triclabendazole Triclabendazole, sold under the brand name Egaten among others, is a medication used to treat fascioliasis and paragonimiasis. It is very effective for both conditions. Treatment in hospital may be required. It is taken by mouth with typically ...

, have been used in control of ''F. magna'' infection in cervids. However, the results have differed between different authors. In the same way as for ''F. hepatica'', triclabendazole seems to be the most effective against ''F. magna''. Fascioloidosis of cervids was successfully controlled with triclabendazole in the United States, and triclabendazole with levamizole in Hungary, Canada, Austria, and Croatia. In contrast, rafoxanide is commonly used in treatment in Czech Republic Slovakia and Hungary. Nevertheless, recent studies suggested that use of rafoxanide in control of ''F. magna'' infection should be considered. Unfortunately, rafoxanide in a commercial drug called Rafendazol Premix is the only registered drug for wild ruminants. Triclabendazole and others are produced as drugs for domestic animals and it can be used in free-living animals only with special permit. In some cases, it may be difficult to determine if ''F. magna'' or a different fluke such as '' Fasciola hepatica'' or '' Fasciola gigantica'' is causing pathology since all these flukes will have the same clinical signs. In the case that the identity of the trematode cannot be determined, the drug

can be used since this will deal with all three parasites.

As human food

In North America, especially in

Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...

, flukes found inside deer livers are sometimes consumed by humans, sautéed in butter. They are served as "liver butterflies", "little livers" or "little flapjacks".

References

External links

*
Control of fascioloidosis in Croatia (PDF format)Final diagnosis: ''Fascioloides magna'' in spinal cord (PDF format)Viral, parasitic and prion diseases of farmed deer and bison (PDF format)
{{Taxonbar, from=Q3376138 Fasciolidae Ruminant diseases Veterinary helminthology Animals described in 1875