The lancet liver fluke, Dicrocoelium dendricitum, is found throughout Europe, Asia, Africa, North America and Australia. (Roberts and Janovy Jr, 2008)
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)
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)
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 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)
There is no parental investment in the lancet liver fluke.
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)
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)
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)
The adult lancet liver fluke feeds on the liver cells of the definitive host. (Roberts and Janovy Jr, 2008)
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)
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.
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)
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)
This species has no conservation status. (Roberts and Janovy Jr, 2008)
Rita Grunberg (author), Rutgers University, Shannon Hahn (author), Rutgers University, David V. Howe (editor), Rutgers University.
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
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.
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
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
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
an animal which directly causes disease in humans. For example, diseases caused by infection of filarial nematodes (elephantiasis and river blindness).
either directly causes, or indirectly transmits, a disease to a domestic animal
uses smells or other chemicals to communicate
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
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.
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).
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.
This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
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.
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.
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.
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.
breeding takes place throughout the year
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.