Flukes

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Flukes
Botulus microporus

Botulus microporus

Systematics
without rank: Multicellular animals (Metazoa)
without rank: Primordial mouths (protostomia)
Trunk : Flatworms (Plathelminthes)
Class : Flukes
Scientific name
Trematoda
Rudolphi , 1808

The flukes (Trematoda) form a class of parasitic flatworms (Plathelminthes). The class includes about 6000 species. The body shape is mostly leaf-shaped, but sometimes also cylindrical. There are adhesive organs (suction cups) on the abdomen. The intestine is usually forked and closed blindly. One example is the lungworm .

features

Flukes are between 0.2 and 165 millimeters long. The body shape is usually flat and long to stocky. Only the pair of leeches or vein leeches have an almost round cross-section. Flukes have a blind-ended digestive tract and specialized sensory organs. The mouth of the suction worms sits at the front lower end of the body and is provided with a mouth suction cup. There is also an abdominal suction cup. The majority of the flukes attach themselves to the species-specific seat in the host organism with the help of the muscular suction cups (also known as adhesive disks) . Most species are hermaphrodites : every animal has male and female genital organs, i. i.e., they are hermaphroditic and can fertilize each other as well as themselves (the latter only if no sexual partner is available).

The majority of the species are characterized by two larval stages living in the wild for a short time. In particular, the first free-living larva , the hair-coated Miracidium , refers to the more original relatives among the flatworms, the free-living turbellarians . The name is derived from τρηματώδης - having an opening for a channel to the intestines (from gr. Τρημα hole, opening, gap).

Life cycle

The flukes are consistently endoparasites with extremely complex life cycles: The animals generally need several host species in order to be able to fully pass through their life cycle. The host excretes the eggs with the faeces (rarely with the urine). If they get into the water, ciliated larvae , the so-called miracidia , hatch . Every Miracidium swims around in the water until its low energy reserves are exhausted or until, with a little luck, it encounters a snail suitable for further development. The miracidium then bores itself into a species-specific tissue of the snail and transforms itself through metamorphosis into a brood tube ( sporocyst ). Daughter sporocysts or rod larvae ( redia ) develop in this through budding and migrate into the midgut gland of the snail. The rod larvae produce further rod larvae, which then produce new larval forms, so-called tail larvae ( cercariae ). If the development takes place via daughter sporocysts, these produce cercariae without further reproduction. The cercariae leave the snail and invade a second intermediate host or are swallowed by it and transform into metacercaria through the separation of cyst material . Often the second intermediate hosts are fish. In these, the parasites can trigger significant changes in behavior.

In the Fasciolidae family , the cercariae attach to aquatic plants, where they form cysts and thus become metacercarias. In addition, there are also exceptions in other suction worm families with regard to the second intermediate host. The metacercariae reach the definitive host, mammals or birds through food. The covering of the cyst breaks open and the young worms usually settle in the digestive tract, but in some species also in the liver, bloodstream or lungs. This is where sexual maturity and mating take place.

distribution

Flukes occur almost everywhere in the world where their host animals thrive. The adult worms parasitize many vertebrate species. All species of flukes are strictly host-specific for the first intermediate host (always a snail ) - for the ultimate host (a vertebrate), however, there is no distinctive host-specificity. The great liver fluke ( Fasciola hepatica ) z. B. parasitizes due to the eating habits of the final hosts mainly in cattle and sheep, but can easily parasitize in humans.

Flukes as pathogens

The great liver fluke is an endoparasite that can a. parasitizes in the bile ducts in sheep , goats and cattle and causes edema and damage to the liver tissue. In cattle, the infection heals with relatively few consequences, in sheep and goats, on the other hand, the infection with the great liver fluke is fatal without veterinary treatment. Epidemics are common in Europe and Australia .

The flukes, known as pair or vein gel, infest the blood of livestock and humans and cause the severe clinical picture of schistosomiasis or schistosomiasis , which is common in tropical climates . The genera Bilharziella , Ornithobilharzia and Trichobilharzia also come in Europe at ducks birds before and call the man who is but only as accidental host occurs, the clinical picture of Cercaria Dermatitis forth.

In addition to these two examples, there is a large number of other human and animal pathogenic species.

In the moderate climatic zones and thus also in Europe a. due to a variety of hygiene measures, the parasitological importance of flukes for humans can be classified as rather insignificant. In the case of wild and farm animals, on the other hand, severe worming can sometimes be recorded.

Systematics

literature

  • Key to the Trematoda , vol. 1 Gibson, DI, Jones, A., and Bray, RA (2002) ISBN 0-85199-547-0

See also

Web links

Commons : Flukes  - Collection of images, videos and audio files

Individual evidence

  1. Weird Guests , NZZ January 23, 2008, accessed June 4, 2014