Fascioloides magna

Geographic Range

Fascioloides magna resides in the liver of their definitive host Odocoileus virginianus, which is the white-tailed deer. These deer are commonly found in North America, particularly southeastern United States, therefore, so are these liver flukes. There have been other reports where they have found this parasite fairly prominent in deer in the Pacific northwest, New York, the Great Lakes states such as the Upper Peninsula of Michigan, and southern Canada. Fascioloides magna is also indigenous in livestock and other deer from the Cervidae family living in Europe. Therefore, they primarily occupy only these two continents, but Fascioloides magna has been seen sporadically in various parts of the world, which is due to the introduction of foreign species and the shipment of infected livestock. (Foreyt, 1990; Michigan Department of Natural Resources, 2010; Mulvey, et al., 1991)


Fascioloides magna is primarily found only in the liver of their definitive hosts Odocoileus virginianus, the white-tailed deer. Even though white-tailed deer can be distributed in various regions, they are more likely to be found in deer inhabiting lowland swamps and other wetland habitats where they have access to their intermediate hosts, freshwater snails. These snails include Lymnaea humilis, L. palustris, and L. stagnalis. Fascioloides magna can occupy other hosts other than the white-tailed deer. They reside primarily in the livers of sheep and cattle. However, these flukes can migrate to other organs such as the lungs or kidneys. (Campbell and Todd, 1954; Foreyt and Todd, 1976; Foreyt and Todd, 1978)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams
  • temporary pools

Physical Description

The name Fascioloides magna meaning "large band" provides a general description of this trematode. They are long, flat, and oval in shape. They have been described as resembling bloodflukes or leeches. Fascioloides magna are purple-gray in color and are normally found encapsulated in a dark-muddy fibrous tissue. Additionally, these flukes are found in a wide range of sizes. They are normally between 15-30mm wide, 30-100mm long, and 2-5mm thick. (Michigan Department of Natural Resources, 2010)

  • Range length
    15 to 30 mm
    0.59 to 1.18 in


After development for some time in the definitive host, adult flukes can deposit 20,000 to 30,000 eggs per day within the cavity or the ducts of the host liver. These eggs have a thick wall with an operculum, which is essentially a door where the organism hatches from at a later stage. From the liver, the eggs move down the intestine and exit the host via feces. Once exiting from the host, the egg is still only a single cell. These eggs develop and hatch within moist feces, shallow water, or any wet environment. After seven to nine days, one can see Fascioloides magna's development via different light shadings on the egg. This stage in development is called the morula stage. On the eleventh day, the anterior end of the egg is void of the embryo and the yolk globules. This absence is known as the mucoid plug. Later, on the fifteenth day, cilia are seen on the organism as flickering motions. By the seventeenth day, the miracidium is fully developed. After twenty-five days, the eggs hatch at night into free-swimming miracidium. From here, the miracidium needs to seek out their intermediate host, a snail. After penetrating a snail, the parasite loses its cilia and develops into a sporocyst form, which produces redia and daughter redia. Within the redia, another stage, the cercariae develops. After approximately four days, the cercariae emerge from the redia and continue its way out of the snail into the external environment. To proceed to the next stage, the cercariae encyst on vegetation, becoming metacercariae, where the definitive host grazes. After migrating to the gut, the larvae burrow out of the intestine to the liver and the larvae develops into an adult after approximately three months. The cycle begins again. (Campbell, 1961; Michigan Department of Natural Resources, 2010; Mulvey, et al., 1991)


Fascioloides magna is a monoecious trematode, which means that it possesses both female and male reproductive systems. Thus, Fascioloides magna does not have any particular mating system since it is self-fertilizing. (Prugnolle, et al., 2005)

As a parasite, Fascioloides magna undergoes a complex life cycle involving an alternation between asexual and sexual reproduction. A single adult can produce up to 20,000-30,000 eggs per day in the definitive host. After being deposited in the external environment, the eggs hatch into miracidium. Then, these miracidium seek their second host, penetrate its skin, and begin asexual reproduction by producing rediae and daughter rediae. These rediae produced are genetically identical to each other. Afterwards, the redia emerge from the intermediate host as cercariae and they encyst on vegetation, becoming metacercariae. Once eaten by a definitive host, sexual reproduction occurs. After full development, Fascioloides magna produces male and female gametes, which fuse together to form a zygote and becomes encapsulated, forming an egg. (Michigan Department of Natural Resources, 2010; Prugnolle, et al., 2005)

  • Breeding season
    In good conditions, it takes Fascioloides magna approximately 5 months to complete its life cycle.
  • Range number of offspring
    20,000 to 30,000
  • Average number of offspring

Fascioloides magna is a hermaphroditic parasite and it does not demonstrate any parental investment in its offspring.

  • Parental Investment
  • no parental involvement


The lifespan for Fascioloides magna solely depends on the lifespan of its host, whether it is the white-tailed deer, sheep, or cattle.


The behavior patterns of the miracidium stage involve a wide range of mobility and may be random. They move in the horizontal plane with very quick motions; however, there is not much movement in the vertical plane. Whenever they do move, they are rotating about their axis either clockwise or counterclockwise. In general, the miracidium can swim actively for eight to twelve hours and in the presence of a snail, will move toward the snail. However, the miricidium is highly affected by temperature. In low temperatures, the miracidium decreases its swimming speed. This enables the miracidium to increase its longevity by conserving their energy resources. Even though the miracidium are increasing their rate of survival with energy conservation, they decrease their ability to seek their intermediate host thereby preventing them from reaching the next stage of their life cycle.

There are no known observations on the behavior of Fascioloides magna in its redia stage.

Once the cercariae emerge from their intermediate host, they possess tails that propel them to seek out vegetation. Upon finding vegetation, the cercariae encyst (now called metacercariae) to protect themselves from any harsh conditions the external environment may bring.

Once ingested by the definitive host, Fascioloides magna burrows out of the intestine and migrates to the liver in order to undergo sexual reproduction. From here, Fascioloides magna is able to migrate throughout the parenchyma of the liver and infect other organs as long as the host immune system does not encapsulate them, limiting their migration. (Campbell and Todd, 1954; Campbell, 1961)

Communication and Perception

There are no known communication or perception features for Fascioloides magna.

Food Habits

Since Fascioloides magna parasitizes primarily the liver of their hosts, they feed solely on the host blood through the use of their mouths. In the sporocyst stage, they do not have a digestive system; therefore, they feed by absorption through their tegument. (Foreyt and Parish, 1990)

  • Animal Foods
  • blood
  • body fluids


There are no known predators of Fascioloides magna.

  • Known Predators
    • There are no known predators.

Ecosystem Roles

Fascioloides magna acts as a parasite as its role in the ecosystem. In their intermediate hosts, they have no impact on the organism. However, they do play a big role in their defintive host such as the white-tailed deer and sheep. In infected female deer, Fascioloides magna causes them to be heavier overall, in poorer condition, and breed earlier. Furthermore, heavily infected deer have a greater tendency to die during severe winters and starvations versus non-infected ones. The pathogenicity of the white-tailed deer is very mild compared to that of sheep. Fascioloides magna has a very large influences on sheep populations if they get infected with this liver fluke. Fascioloides magna does great damage to the liver tissues and the surrounding area, which leads to a quick death if infected with only a few flukes. (Michigan Department of Natural Resources, 2010; Mulvey, et al., 1994)

Economic Importance for Humans: Positive

There are no known resources that demonstrate positive economic importance by Fascioloides magna.

Economic Importance for Humans: Negative

Fascioloides magna does not affect humans directly because their main host involves animals from the Cervidae family or ruminants. However, Fascioloides magna has very adverse effects on livestock economics. If the parasite is ingested by sheep, they can do much damage to the animal. Unlike deer and cattle, the immune response of sheep do not encapsulate the parasite, allowing the migration of the parasite through the liver tissue. This can cause severe hemmorhaging and the onset of peritonitis. Fascioloides magna causes such severe damage to the sheep that it only takes two or three of these flukes to kill the animal. This strong pathogenicity in sheep can enduce a great amount of stress for the sheep farmer and cause a large amount of economic loss.

Even though cattle are able to encapsulate and reduce the migration of the parasite, the fact that liver flukes still reside in the tissue after slaughtering greatly degrades the value of the meat and renders it unmarketable. Therefore, Fascioloides magna has a strong economic influence on the livestock industry if they ever infect a herd of sheep or cattle. (Michigan Department of Natural Resources, 2010)

Conservation Status


Stephanie Nguyen (author), University of Michigan-Ann Arbor, Heidi Liere (editor), University of Michigan-Ann Arbor, John Marino (editor), University of Michigan-Ann Arbor, Barry OConnor (editor), University of Michigan-Ann Arbor, Renee Mulcrone (editor), Special Projects.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map


living in landscapes dominated by human agriculture.


reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat

causes or carries domestic animal disease

either directly causes, or indirectly transmits, a disease to a domestic animal


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


marshes are wetland areas often dominated by grasses and reeds.


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).


an animal that mainly eats blood


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


living in residential areas on the outskirts of large cities or towns.


a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.

year-round breeding

breeding takes place throughout the year


Campbell, W., A. Todd. 1954. Natural infections of Fascioloides magna in Wisconsin sheep. The Journal of Parasitology, 40 (1): 100.

Campbell, W. 1961. Notes on the egg and miracidium of Fascioloides magna, (Trematoda). Transactions of the American Microscopical Society, 80 (3): 308-319. Accessed April 02, 2011 at http://www.jstor.org/stable/3223642.

Conboy, G., T. O'Brien, D. Stevens. 1988. A natural infection of Fascioloides magna in a Llama (Lama glama). The Journal of Parasitology, 74 (2): 345-346. Accessed April 06, 2011 at http://www.jstor.org/pss/3282468.

Foreyt, W. 1990. Domestic sheep as a rare definitive host of the large American liver fluke Fascioloides magna. The Journal of Parasitology, 76 (5): 736-739.

Foreyt, W., S. Parish. 1990. Experimental infection of liver flukes (Fascioloides magna) in a llama (Lama glama). Journal of Zoo and Wildlife Medicine, 21(4): 468-470.

Foreyt, W. 1992. Experimental Fascioloides magna infections of mule deer. Journal of Wildlife Disease, 28 (2): 183-187. Accessed April 06, 2011 at http://www.jwildlifedis.org/cgi/reprint/28/2/183.pdf.

Foreyt, W., W. Samuel, A. Todd. 1977. Fascioloides magna in white-tailed deer (Odocoileus virginianus): Observations on the pairing tendency. The Journal of Parasitology, 63 (6): 1050-1052. Accessed April 06, 2011 at http://www.jstor.org/stable/info/3279843?seq=1.

Foreyt, W., A. Todd. 1976. Development of the large American liver fluke, Fascioloides magna, in white-tailed deer, cattle, and sheep. The Journal of Parasitology, 62 (1): 26-32. Accessed April 06, 2011 at http://www.jstor.org/stable/info/3279036?seq=1.

Foreyt, W., A. Todd. 1978. Experimental infection of lymnaeid snails in Wisconsin with miracidia of Fascioloides magna and Fasciola hepatica. The Journal of Parasitology, 64 (6): 1132-1134. Accessed April 06, 2011 at http://www.jstor.org/pss/3279747.

Foreyt, W., A. Todd. 1972. The occurrence of Fascioloides magna and Fasciola hepatica together in the livers of naturally infected cattle in South Texas, and the incidence of the flukes in cattle, white-tailed deer, and feral hogs. The Journal of Parasitology, 58 (5): 1010-1011. Accessed April 06, 2011 at http://www.jstor.org/stable/info/3286607?seq=1.

Friedl, F. 1961. Studies on larval Fascioloides magna. I. Observations on the survival of rediae in vitro. The Journal of Parasitology, 47 (1): 71-75. Accessed April 06, 2011 at http://www.jstor.org/stable/3274982.

Friedl, F. 1962. Studies on larval Fascioloides magna. II. In vitro survival of axenic rediae in amino acids and sugars. The Journal of Parasitology, 47 (2): 244-247. Accessed April 06, 2011 at http://www.jstor.org/pss/3275299.

Glazener, W., F. Knowlton. 1967. Some endoparasites found in welder refuge deer. The Journal of Wildlife Management, 31 (3): 595-597. Accessed April 06, 2011 at http://www.jstor.org/pss/3798147.

Michigan Department of Natural Resources, 2010. "Deer Liver Fluke" (On-line). Michigan Department of Natural Resources: Wildlife Disease. Accessed April 02, 2011 at http://www.michigan.gov/dnr/1,1607,7-153-10370_12150_12220-26639--,00.html.

Mulvey, M., J. Aho, C. Lydeard, P. Leberg, M. Smith. 1991. Comparative population genetic structure of a parasite (Fascioloides magna) and its definitive host. Evolution, 45 (7): 1628-1640. Accessed April 02, 2011 at http://www.jstor.org/stable/2409784?cookieSet=1.

Mulvey, M., J. Aho, O. Rhodes, Jr.. 1994. Parasitism and white-tailed deer: Timing and components of female reproduction. Oikos, 70 (2): 177-182. Accessed April 06, 2011 at http://www.jstor.org.proxy.lib.umich.edu/stable/3545628?seq=4.

Prugnolle, F., H. Liu, T. de Meeus, F. Balloux. 2005. Population genetics of complex life-cycle parasites: an illustration with trematodes. International Journal for Parasitology, 35 (3): 255-263.

Qureshi, T., D. Davis, D. Drawe. 1990. Use of albendazole in feed to control Fascioloides magna infections in captive white-tailed deer (Odocoileus virginianus). Journal of Wildlife Disease, 26 (2): 231-235. Accessed April 06, 2011 at http://www.jwildlifedis.org/cgi/reprint/26/2/231.pdf.

Qureshi, T., D. Drawe, D. Davis, T. Craig. 1994. Use of bait containing triclabendazole to treat Fascioloides magna infections in free ranging white-tailed deer. Journal of Wildlife Disease, 30 (3): 346-350. Accessed April 06, 2011 at http://www.jwildlifedis.org/cgi/content/abstract/30/3/346.

Wobeser, G., A. Gajadhar, H. Hunt. 1985. Fascioloides magna: Occurrence in Saskatchewan and distribution in Canada. National Institute of Health, 26: 241-244. Accessed April 06, 2011 at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1680019/.