Fascioloides Magna

Fasciolid flukes are among the largest and best known flatworms that have considerable historical and veterinary significance. One of the first infectious agents to be discovered and implicated in causing disease was no doubt the liver fluke, Fasciola hepatica, causative agent of liver rot disease in domestic ruminants. Although fasciolids mostly parasitize large herbivorous mammals, three species Fasciola hepatica, F. gigantica, and Fasciolopsis buski regularly infect humans.2 All members of the Fasciolinae family colonize either the bile ducts or liver parenchyma and feed on blood of their definitive hosts.

Fascioloides magna, also known as giant liver fluke, large American liver fluke or deer fluke, is a large parasite of North American domestic and wild ungulates, with its body dimensions of 3-7.3 × 2-3 cm and thickness 0.2-0.45 cm. This parasite belongs to phylum Platyhelminthes (flatworms), class Trematoda. Most flatworms are hermaphroditic, and complete male and female reproductive systems occur in each individual. Giant liver flukes infect a large spectrum free-living animals, such as deer, moose, reindeer, cattle, sheep, and goat. Like some other trematodes, the F. magna has a complex life cycle that includes two hosts, aquatic snails as intermediate hosts and ruminants as definitive hosts. Immature parasites enter the body of the snail via the foot, whereas the next stage of its life cycle is physically attached to vegetation and is ingested by grazing animals.

The infection in definitive hosts entails the migration of immature flukes, during which time they search for other flukes and congregate in thin-walled fibrous pseudocapsules, which typically contains two or more adult flukes. Cysts are filled with dark-green liquid containing degraded bilirubin and fluke. The physiological effects of high egg production may be highly deleterious to the host, because the eggs may block bile ducts or stimulate the production of a pseudocyst, which may rupture the hepatic wall. In deer, infection may proceed nonlethally, but in dead-end hosts (goat, sheep), it may cause death.3 Transmission to domestic ruminants takes place in areas where pastures are shared with wild ungulates. Transfer of the fluke to domestic sheep and cattle herds can lead to large economic costs due to mortality of the animals and destruction of infected livers.


  1. Highland cattle and Radix labiata, the hosts of Fascioloides magna
  2. Evolutionary Origins, Diversification, and Biogeography of Liver Flukes (Digenea, Fasciolidae)
  3. Life history and biology of Fascioloides magna (Trematoda) and its native and exotic hosts

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