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. As with other digenean trematodes, the life cycle includes intramolluscan phase in snails. 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) near Turin, 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 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.
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. At the same time, Salomon (1932) diagnosed the fluke in one hunted red deer near Görlitz (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.
right|320px|thumb|Distribution of F. magna in Europe
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 Gratzen Mountains; (2) the area along the Vltava River on the Vltava-Týn hills near Hluboká nad Vltavou and Bechyně; (3) Písek and Milevsko county; (4) the Brdy mountains and the Hřebeny mountains. 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 water plant at the Danube River in Slovakia. The parasite has spread through whole Slovak Danube watershed. 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 and 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. 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. In Europe, F. magna occurs commonly in red deer (Cervus elaphus), fallow deer (Dama dama) and roe deer (Capreolus capreolus). In North America, the giant liver fluke is commonly found in cattle, sheep and goats in areas where F. magna is enzootic in deer.
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 epoch, and overlapped with white-tailed deer in some parts of North America. They might have encountered F. magna in these shared biotopes.
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Black-tailed deer
! style="text-align: left;white-space:nowrap;font-weight:normal"|Odocoileus hemionus columbianus
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Caribou
! style="text-align: left;white-space:nowrap;font-weight:normal"|Rangifer tarandus
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Collared peccary
! style="text-align: left;white-space:nowrap;font-weight:normal"|Dicotyles tajacu
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Goat
! style="text-align: left;white-space:nowrap;font-weight:normal"|Capra hircus
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Horse
! style="text-align: left;white-space:nowrap;font-weight:normal"|Equus caballus
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Llama
! style="text-align: left;white-space:nowrap;font-weight:normal"|Lama glama
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Moose
! style="text-align: left;white-space:nowrap;font-weight:normal"|Alces alces
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Mule deer
! style="text-align: left;white-space:nowrap;font-weight:normal"|Odocoileus hemionus hemionus
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Sheep
! style="text-align: left;white-space:nowrap;font-weight:normal"|Ovis aries
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Yak
! style="text-align: left;white-space:nowrap;font-weight:normal"|Bos grunniensis
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Red deer
! style="text-align: left;white-space:nowrap;font-weight:normal"|Cervus elaphus
! style="text-align:central;white-space:nowrap;font-weight:normal"| Lethargy, depression, weight loss and decreased quality of antlers can occur sporadically. 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, elevation of γ-globulins, and increase of eosinophils 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. While American authors have not observed any clinical symptoms in cattle,
(3) Aberrant hosts
thumb|250px|Necropsy of goat infected with F. magna: fibrin between liver and diaphragmAberrant hosts of F. magna are sheep and goats. However, the course of infection is similar in guinea pigs, and chamois (Rupicapra rupicapra) In aberrant hosts, flukes do not mature and migrate until the host dies. Hepatic lesions in aberrant hosts generally include firm adhesions of the liver to the diaphragm, black pigmentation, hematomas, necroses, and haemorrhagic tracts in which juvenile flukes are located.
Intermediate hosts
250px|thumb|Intermediate hosts of F. magna in Europe: freshwater snails, G. truncatula (above) and R. peregra (below).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 Lymnaeidae. 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. 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 is an intermediate host of the giant liver fluke in Europe. Recent studies indicate that another lymnaeid snail, Radix peregra, 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 environment 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.
{| class="wikitable"
! style="width:20%" |Snail species
! style="width:9%" |Naturally infected
! style="width:9%" |Experimentally infected
! style="width:15%" |Country
! style="width:5%" |Reference
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! style="text-align:left;white-space:nowrap;font-weight:bold"|NORTH AMERICA
! style="text-align:central;white-space:nowrap;font-weight:normal"|
! style="text-align:central;white-space:nowrap;font-weight:normal"|
! style="text-align:central;white-space:nowrap;font-weight:normal"|
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Fossaria (Galba) bulimoides techella
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|United States
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Fossaria (Galba) modicella
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|United States, Canada
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Pseudosuccinea columella
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|United States
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Stagnicola palustris
! style="text-align:central;white-space:nowrap;font-weight:normal"|no
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|United States
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Stagnicola (Lymnaea) caperata
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|United States
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Lymnaea ferruginea
! style="text-align:central;white-space:nowrap;font-weight:normal"|no
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|United States
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Austropeplea (Lymnaea) tomentosa
! style="text-align:central;white-space:nowrap;font-weight:normal"|no
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|Australia*
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:bold"|EUROPE
! style="text-align:central;white-space:nowrap;font-weight:normal"|
! style="text-align:central;white-space:nowrap;font-weight:normal"|
! style="text-align:central;white-space:nowrap;font-weight:normal"|
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Galba truncatula
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|Czech Republic
! style="text-align:central;white-space:nowrap;font-weight:normal"|
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! style="text-align:left;white-space:nowrap;font-weight:normal"|Radix peregra
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|yes
! style="text-align:central;white-space:nowrap;font-weight:normal"|Czech Republic
! style="text-align:central;white-space:nowrap;font-weight:normal"| Pigment within tissues is a result of migrating of juvenile flukes and it accumulates within hepatic cells without resorption.
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
thumb|250px|Formula of triclabendazole 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. Fascioloidosis of cervids was successfully controlled with triclabendazole in the United States, and triclabendazole with levamizole in Hungary, Austria, In contrast, rafoxanide is commonly used in treatment in Czech Republic
As human food
In North America, especially in Wisconsin, flukes found inside deer livers are sometimes consumed by humans, sautéed in butter. They are served as "liver butterflies", "little livers" or "little flapjacks".
See also
- Fascioliasis
- Fasciola hepatica
<gallery>
Fmagnus.jpg|Relative size of F. magnus to human hand.
</gallery>
References
External links
- Control of fascioloidosis in Croatia (PDF format)
- F. magna and wapiti
- Liver flukes
- Final diagnosis: Fascioloides magna in spinal cord (PDF format)
- Viral, parasitic and prion diseases of farmed deer and bison (PDF format)