Fascioloides magna, also known as Large American liver fluke or Giant liver fluke, is a parasitic flatworm in the class Trematoda, Phylum Platyhelminthes, which grows to a maximum length of 100 millimeters, and is thick and oval in shape. It is distinguished from other members of the genus Fasciola by the lack of an anterior projecting cone. It occurs in domestic and wild ruminants, deer being the normal hosts.

Life cycle

---

The life cycle is not completed in cattle. In this host, pathogenicity is low, and losses are confined primarily to the fluke's destruction of the animal's liver. In sheep and goats, a few parasites can cause death due to extensive fluke migration in the liver parenchyma. In deer, there is little tissue reaction, and the parasites are enclosed in thin, fibrous cysts that communicate with bile ducts. In cattle, F. magna cause severe tissue reaction, resulting in thick-walled encapsulations that do not communicate with bile ducts. In sheep, encapsulations do not develop, and the parasites migrate in the liver and other organs, causing tremendous damage. Histologically, infected livers of cattle, sheep, and deer show black, tortuous tracts formed by migrations of young flukes.

Diagnosis and treatment

---

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.

Oxyclozanide has been reported to be effective against F. magna in white-tailed deer, and rafoxanide has been used successfully against natural infections in cattle. Albendazole (7.5 mg/kg), clorsulon (15 mg/kg), and closantel (15 mg/kg) have shown efficacy against this fluke in sheep. Currently no products are approved for use against this fluke in the USA. Deer are required for completion of the life cycle; if they can be excluded from the areas grazed by cattle and sheep, then infection can be controlled. Control of the intermediate host (lymnaeid snails) may be possible once it has been identified in a region and the nature of its habitat examined.

See also

---

• Fascioliasis

External link

---

• Viral, parasitic and prion diseases of farmed deer and bison (PDF format)

Flatworms | Parasitology