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Life-history stages of the trematode flatworm
Fasciola hepatica from 1911
Encyclopaedia Britannica
Trematodes are small parasitic flatworms that use vertebrates as their definitive host, and molluscs (usually freshwater snails or land snails) as their intermediate host. To accomplish this, they have several varied life cycle stages.
The life cycle of a typical digenean trematode can be thought to begin when its egg is immersed in water. Following this, a miracidium hatches, which swims to find a mollusc host. The miracidia go through several stages in the mollusc host, eventually emerging as motile cercarial larvae.[1] The cercaria either infects vertebrates through the skin or is ingested. In its vertebrate host, the cercaria matures to an adult form, and lays eggs that are discharged with the host faeces or urine. In the presence of open water, the eggs hatch and the miracidium stage of life is reached again.
Contents
- 1 Typical life cyle stages
- 2 Deviations from the typical life cycle
- 3 Representations of life cycles of several different trematode species
- 4 References
- 5 See also
- 6 External links
Typical life cyle stages
Metacercariae of
Clinostomum phalacrocoracis in fish
[2]
Bucephalid cercaria larva from Ernst Haeckel's
Kunstformen der Natur (1904): The tail's furcae give the impression of horns, hence the genus name
Bucephalus meaning "ox head".
While the details vary with each species, the general life cycle stages are:
- Egg – discharged either in open water or in intestine of definitive host
- Miracidium (plural miracidia) – a free-living motile form, it is covered with cilia, and settles in the mollusc to become a sporocyst.[3]
- Sporocyst – an elongated sac, it produces either rediae or more sporocysts.[4]
- Redia (plural rediae) – a larval form with an oral sucker, it will produce either more rediae, or cercariae.[4]
- Cercaria (plural cercariae) – the larval form of the parasite, it develops within the germinal cells of the sporocyst or redia.[4] A cercaria has a tapering head with large penetration glands.[3] It may or may not have a long swimming "tail", depending on the species.[4] The motile cercaria finds and settles in a host where it will become either an adult, or a mesocercaria, or a metacercaria, according to species.
- Mesocercaria – a cercaria little modified but resting
- Metacercaria – a cercaria encysted and resting
- Adult – the fully developed mature stage, it is capable of sexual reproduction.
Deviations from the typical life cycle
Not all trematodes follow the typical sequence of eggs, miracidia, sporocysts, rediae, cercariae, and adults. In some species, the redial stage is omitted, and sporocysts produce cercariae. In some species, the cercaria develops into an adult within the same host.
Many digenean trematodes require two hosts, one (typically a snail) where asexual reproduction occurs in sporocysts, the other a vertebrate (typically a fish) where the adult form engages in sexual reproduction to produce eggs. In some species (for example Ribeiroia) the cercaria encysts, and waits until the host is eaten by a third host, in whose gut it emerges and develops into an adult.
Most trematodes are hermaphroditic, but members of the family Schistosomatidae are dioecious. Males are shorter and stouter than the females.[3]
Representations of life cycles of several different trematode species
Life cycle stages of a digenean human parasite,
Schistosoma japonicum
Life cycle stages of a digenean fish parasite,
Bucephalus polymorphus
Life cycle stages of trematode species that cause "swimmer's itch"
References
- ^ "2. Fish Diseases (Cont'd.) 2.1.4 Parasitic Diseases". FAO of the UN Food and Agriculture Organization of the United Nations. Retrieved 18 February 2011.
- ^ Caffara, M., Davidovich, N., Falk, R., Smirnov, M., Ofek, T., Cummings, D., Gustinelli, A. & Fioravanti, M. L. 2014: Redescription of Clinostomum phalacrocoracis metacercariae (Digenea: Clinostomidae) in cichlids from Lake Kinneret, Israel. Parasite, 21, 32. doi:10.1051/parasite/2014034 PubMed PMC 4078730
- ^ a b c "Schistosoma". Australian Society for Parasitology. Retrieved 19 February 2011.
- ^ a b c d "Glossary". VPTH 603 Veterinary Parasitology. University of Pennsylvania School of Veterinary Medicine.
See also
- Bucephalus polymorphus
- Trematode infection
- Apicomplexa lifecycle stages
External links
- Life cycle of Schistosoma mansoni
UpToDate Contents
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English Journal
- Pathology and first report of natural eye infection with the trematode Philophthalmus gralli (Digenea, Philophthalmidae) in Tinamus major (Tinamiformes, Tinamidae), Costa Rica.
- Rojas D, Soto C, Rojas A.SourceLaboratorio de Helmintología, Centro de Investigaciones en Enfermedades Tropicales, Facultad de Microbiología, Universidad de Costa Rica, San Pedro Montes de Oca, San José 2060, Costa Rica.
- Parasitology international.Parasitol Int.2013 Dec;62(6):571-4. doi: 10.1016/j.parint.2013.08.006. Epub 2013 Aug 28.
- The eye-fluke Philophthalmus gralli (Philophthalmidae Looss, 1899) was found in six birds known as great tinamous (Tinamus major) reared in a wild animal shelter located in Alajuela, Costa Rica. The birds presented conjunctival hyperemia, blepharitis, anorexia and weakness. Some of them suffered fro
- PMID 23993998
- Increased Parasitism of Limpets by a Trematode Metacercaria in Fisheries Management Areas of Central Chile: Effects on Host Growth and Reproduction : Management Areas and Parasitism.
- Aldana M, Pulgar JM, Orellana N, Patricio Ojeda F, García-Huidobro MR.SourceEscuela de Pedagogía en Biología y Ciencias, Facultad de Ciencias de la Educación, Universidad Central de Chile, Santa Isabel 1278, 6° piso, Santiago, Chile, maldanap@ucentral.cl.
- EcoHealth.Ecohealth.2013 Oct 19. [Epub ahead of print]
- The rapid increase in body size and abundance of most species inside Management and Exploitations Areas for Benthic Resources (MEABRs) has led to the proposal of these areas as a good complement for achieving the conservation objectives of Marine Protected Areas (MPAs). However, when evaluating MEAB
- PMID 24142461
Japanese Journal
- 福井県のサンショウウオに見られたメタセルカリア結節症
- 川内 一憲/長谷川 巌/田中 幸枝/小鍛冶 優/百崎 孝男/木元 久/藤井 豊,長谷川 巌,田中 幸枝 [他],小鍛冶 優,百崎 孝男,木元 久,藤井 豊,KAWAUCHI Kazunori,HASEGAWA Iwao,TANAKA Yukie,KOKAJI Masaru,MOMOSAKI Takao,KIMOTO Hisashi,FUJII Yutaka
- 福井大学医学部研究雑誌 12(1.2), 49-51, 2011-12-26
- NAID 110009455681
- 阿武隈山地北部のトウホクサンショウウオにおける皮膚メタセルカリア結節の発生とその増加
Related Links
- metacercaria met·a·cer·car·i·a (mět'ə-sər-kār'ē-ə) n. pl. met·a·cer·car·i·ae (-ē-ē') The encysted maturing stage of a trematode in its intermediate host prior to transfer to the definitive host, usually representing the organism's infectious ...
- Metacercaria (plural, metacercariae) The encysted stage of a fluke larva that produces infection in human beings. Mentioned in: Fluke Infections metacercaria [met″ah-ser-kar´e-ah] (pl. metacerca´riae) The encysted resting or pl. ...
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