''Fascioloides magna'', also known as giant liver fluke, large American liver fluke or deer fluke, is
trematode parasite that occurs in wild and domestic
ruminants 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 sucker. The flukes are reddish-brown in colour and are covered by
tegument
Tegument may refer to:
* Integumentary system, a protective organ system forming the outermost layer of an animal's body
* Tegument (helminth) Tegument is a term in helminthology for the outer body covering of members of the phylum Platyhelminthe ...
. 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. ...
n
trematodes, 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.
In 1875, Bassi observed massive deaths of red deer in the Royal Park (now
La Mandria Regional Park
La Mandria Regional Park is a park in the comuni of Venaria Reale and Druento, near Turin, northern Italy. Founded in 1978 by the regional council of Piedmont, it occupies a wide area between the Stura di Lanzo torrent and the north-western part ...
) near
Torino, Italy. The signs were similar to well known
fasciolosis 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 ''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
The Miracidium is the second stage in the life cycle of trematodes. When trematode eggs are laid and come into contact with fresh water, they hatch and release miracidium. In this phase, miracidia are ciliated and free-swimming. This stage is comp ...
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 and oxygen tension, 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. 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 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 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 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
The elk (''Cervus canadensis''), also known as the wapiti, is one of the largest species within the deer family, Cervidae, and one of the largest terrestrial mammals in its native range of North America and Central and East Asia. The common ...
, 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 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 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 near Görlitz
Görlitz (; pl, Zgorzelec, hsb, Zhorjelc, cz, Zhořelec, :de:Ostlausitzer Mundart, East Lusatian dialect: ''Gerlz'', ''Gerltz'', ''Gerltsch'') is a town in the Germany, German state of Saxony. It is located on the Lusatian Neisse River, and ...
(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 dama'') and roe deer (''Capreolus capreolus'') were reported by several authors in former Czechoslovakia. 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 cervids 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 of former Czechoslovakia. 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 and Třeboň county, including Nové Hrady Mountains; (2) the area along the Vltava 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 urban ...
; (3) Písek 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 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 i ...
Mountains has epizootiological importance due to possibility of spread of the parasite into the German territory ( Bavaria).[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 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. T]