[1][2] 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.

[3] 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.

[6] 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.

[1][2][4]Adult flukes occur in pairs or groups within a fibrous capsule in the liver parenchyma of the definitive host.

Ciliated miracidia hatch in water and actively seek suitable intermediate hosts that are freshwater snails from family Lymnaeidae.

The sporocysts contain germinal cells that give rise to 1–6 mother rediae (a trematode larval form with an oral sucker).

Mature cercarie spontaneously emerge from the snail host and swim actively in water for up to two hours before encysting on vegetation.

Currently, F. magna occurs only in North America and Europe where suitable habitat exists and susceptible intermediate hosts are found.

[8] 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.

[1] The highest mortality was reported in free ranging roe deer in Písek County in the South Bohemia of former Czechoslovakia.

Moreover, the appearance of F. magna in the Šumava Mountains has epizootiological importance due to possibility of spread of the parasite into the German territory (Bavaria).

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.

F. magna infection of cervids is a considerable problem in northern part of Hungary (Szigetköz) and the southern Danubian territory in the Gemenc area.

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%.

[15][16] 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.

[2] In North America, the common definitive hosts of the giant liver fluke are wapiti (Cervus elaphus canadensis), white-tailed deer (Odocoileus virginianus) and caribou (Rangifer tarandus).

[18] In North America, the giant liver fluke is commonly found in cattle, sheep and goats in areas where F. magna is enzootic in deer.

Other author has observed partial paralysis in naturally infected wapiti caused by migrating juvenile flukes in the spinal cord.

A decrease of haemoglobin, elevation of γ-globulins, and increase of eosinophils in serum was observed in experimentally infected white-tailed deer.

Infections in dead-end hosts are characterized by excessive fibrosis, thick-walled encapsulation of flukes within hepatic parenchyma, and black pigmentation of various tissues.

In cattle, significant elevations of eosinophil counts in periphery blood but only slight increases of AST and GGT have been observed.

[36] While American authors have not observed any clinical symptoms in cattle,[17][36] anorexia and weight loss were recorded in naturally infected bulls in the former Czechoslovakia.

[2] Aberrant hosts die usually within 6 months post-infection and the death is associated with acute peritonitis or extensive haemorrhage caused by migrating flukes.

[42][43] 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.

The dominant feature is a diffuse fibrosis throughout the liver and haemorrhagic migratory tracts containing erythrocytes, black pigment, and cell detritus.

[44] 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.

[1] 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.

When domestic ruminants and deer share the same grazing areas, the presence of disease due to F. magna should be kept in mind.

[8] Several drugs, namely oxyclozanide, rafoxanide, albendazole, diamphenetide, closantel, clorsulon, and triclabendazole, have been used in control of F. magna infection in cervids.

[64] In North America, especially in Wisconsin,[65] flukes found inside deer livers are sometimes consumed by humans, sautéed in butter.