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Dicrocoelium dendriticum

By Rita Grunberg and Shannon Hahn

Geographic Range

The lancet liver fluke, Dicrocoelium dendricitum, is found throughout Europe, Asia, Africa, North America and Australia. (Roberts and Janovy Jr, 2008)

Habitat

Dicrocoelium dendricitum resides in the liver of domesticated animals and other grassland wildlife. The eggs are released in the feces and two other intermediate stages involve infecting landsnails and ants. (Ansari-Lari and Moazzeni, 2006; Roberts and Janovy Jr, 2008)

Physical Description

Dicrocoelium dendricitum has a tapered, lancet-shaped, flattened body and is semitransparent. The vitellaria are in the midsection of the body, and the uterus is on the posterior end of the body. Lobed testes are on the anterior ventral portion and the oral suckers are at the anterior end of the organism. The body length is 6 to 10 mm, ranging from 1.5-2.5 mm in width. Eggs are operculated and are about 36-45 µm long by 22-30 µm wide. The eggs develop into larvae, or miracidium, and then into the juvenile stage called cercariae. The cercariae have tails and a stylet, which are normal characteristics of aquatic cercariae even though D. dendriticum infect organisms in terrestrial environments. The cercariae then develop into metacercariae then finally into their adult stage. (Carney, 1969; Roberts and Janovy Jr, 2008)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    6 to 10 mm
    0.24 to 0.39 in

Development

Eggs are passed in the feces of the definitive host. The feces, along with the eggs are eaten by a snail, which is the intermediate host. A miracidium is released from the egg once it is inside the snail’s intestine. The miracidium then penetrates the intestinal wall band and becomes a mother sporocyst. The sporocyst asexually reproduces, creating numerous daughter sporocysts that contain cercariae. The cercariae leave the sporocyst and are expelled from the snail host in a slime ball. An ant will ingest this slime ball, becoming the second intermediate host of the parasite. Once ingested by the ant, most of the metacercaria encyst in the hemocoel but two or three reach the brain of the ant and are called “brainworms.” The few metacercaria in the brain cause the ant to alter its behavior. When the temperature decreases the ants appear and attach to the top of grass where they do not move. This increases the chance of the ant being eaten by the definitive host, which are grazers of pasture land. Inside the definitive host’s intestine the parasite will migrate to the liver using the bile duct. The metacercaria take about six to seven weeks to mature inside the bile duct and produce eggs after a month. Fertilized eggs are passed out through the feces. (Roberts and Janovy Jr, 2008)

Reproduction

Reproduction and production of eggs occur in the definitive host, a vertebrate such as sheep, cattle or pigs. Thus, reproduction is dependent on transmission between the ant, the second intermediate host, and the definitive host. (Roberts and Janovy Jr, 2008)

Adult Dicrocoelium dendricitum produce both eggs and sperm and can self-fertilize. Within a single sheep, as many as 50,000 adult flukes have been recorded. The breeding interval depends upon how frequently one fluke comes in contact with another or how frequently one fluke develops both egg and sperm to fertilize itself. (Ansari-Lari and Moazzeni, 2006; Roberts and Janovy Jr, 2008)

  • Breeding interval
    The breeding interval is dependent on encounters and development.
  • Breeding season
    There is no breeding season for the lancet liver fluke.
  • Average number of offspring
    500 cercariae in one slime ball
  • Range age at sexual or reproductive maturity (female or asexual)
    6 to 7 weeks
  • Range age at sexual or reproductive maturity (male)
    6 to 7 weeks

There is no parental investment in the lancet liver fluke.

  • Parental Investment
  • no parental involvement

Lifespan/Longevity

The life span of Dicrocoelium dendriticum depends on the development within the hosts and the lifspan of the hosts. The life cycle of this parasite includes two intermediate stages (hosts) and one definitive stage (host). The cercariae in the slime ball will mature once it is consumed by the proper species of snail. The cercariae can take up to five months to mature into metacercariae. Once inside the definitive host the metacercariae take about six to seven weeks to mature and then produce eggs after a month. While it is unknown how long adults live, the lifespan of adults can also depend on the lifespan of the host. (Roberts and Janovy Jr, 2008)

Behavior

The cercariae, metacercariae and adult stages of the lancet liver fluke are all motile, which allows the organisms to travel to the specific areas of the hosts’ body. Adult flukes are confined to the distal areas of the bile ducts. (Carney, 1969; Roberts and Janovy Jr, 2008)

Communication and Perception

The lancet liver fluke is attracted to bile, which allows it to migrate to the bile duct that leads to the liver. The fluke perceives its environment through tactile and chemical cues to find the appropriate area within the definitive host. Lancet liver flukes also find members of its own species (to mate) by migrating to the same location within the hosts’ body. (Roberts and Janovy Jr, 2008)

Food Habits

The adult lancet liver fluke feeds on the liver cells of the definitive host. (Roberts and Janovy Jr, 2008)

  • Animal Foods
  • body fluids

Predation

There are no known predators of this parasite. However, the eggs are eaten by a snail, the cercariae are eaten by an ant and the metacercariae are consumed by the definitive host as the host grazes upon the grass. (Roberts and Janovy Jr, 2008)

Ecosystem Roles

The lancet liver fluke is a parasite. Intermediate hosts include snails, and it is not necessarily host specific. In North America a common host is Cionella lubrica.

The second intermediate host is an ant, and in North America this includes the brown ant, Formica fusca. The cercaria alters the behavior of the ant. The fluke makes the ant attach motionless on a blade of grass so the ant has a higher likelihood of being eaten. This behavioral alteration may be due to a metabolic product produced by the parasite or by a mechanical means.

Definitive hosts include sheep, goats, cattle, pigs and cervids. (Ansari-Lari and Moazzeni, 2006; Carney, 1969; Roberts and Janovy Jr, 2008)

Species Used as Host

Economic Importance for Humans: Positive

There is no positive economic gain for humans from this species. However, the discovery of this parasite's life cycle led to advances in the knowledge of other parasitic life cycles. Therefore, there is an education/research benefit to humans. (Roberts and Janovy Jr, 2008)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

Dicrocoelium dendricitum causes various pathologies in hosts, which can be negative in domestic animals. Symptoms include biliary colic, digestive disturbances, infections, inflammation of the bile ducts and fibrosis. In some cases the liver can become enlarged. Heavy infections render livers unsellable. Treatment for this infection is extremely costly. There have been a few documented cases of human infections of D. dendricitum in Russia, Europe and Asia, and at least one in North America. (Ansari-Lari and Moazzeni, 2006; Roberts and Janovy Jr, 2008)

Conservation Status

This species has no conservation status. (Roberts and Janovy Jr, 2008)

Contributors

Rita Grunberg (author), Rutgers University, Shannon Hahn (author), Rutgers University, David V. Howe (editor), Rutgers University.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

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

Palearctic

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

World Map

agricultural

living in landscapes dominated by human agriculture.

asexual

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.

carnivore

an animal that mainly eats meat

causes disease in humans

an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).

causes or carries domestic animal disease

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

chemical

uses smells or other chemicals to communicate

ectothermic

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

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

heterothermic

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.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

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.

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

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

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

parasite

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

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

sexual

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

solitary

lives alone

tactile

uses touch to communicate

temperate

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).

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

year-round breeding

breeding takes place throughout the year

References

Ansari-Lari, M., M. Moazzeni. 2006. A retrospective survey of liver fluke disease in livestock based on abattoir data in Shiraz, south of Iran. Preventive Veterinary Medicine, Volume 73/ Issue 1: 93-96. Accessed February 13, 2013 at http://www.ncbi.nlm.nih.gov/pubmed/16198433.

Carney, W. 1969. Behavioral and morphological changes in carpenter ants harboring dicrocoeliid metacercariae. American Midland Naturalist, Volume 82/ Issue 2: 605-611. Accessed February 13, 2013 at http://www.mendeley.com/research/behavioral-morphological-changes-carpenter-ants-harboring-dicrocoeliid-metacercariae/.

Roberts, L., J. Janovy Jr. 2008. Foundations of Parasitology. New York: McGraw-Hill Higher Education.

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