Fasciola hepatica

See also: Ditch

The Fasciola hepatica is a trematode responsible for the Fasciolose i.e of a liver fluke. It is a Ver parasitizes liver and bile ducts, prosperous in the Foie of the Mouton S and is occasionally met at the Cheval. Very frequent and very pathogenic in the ruminants, the ditch nourishes Sang and hepatic cells, grows then lays its eggs. But the eggs of ditches cannot hatch in the liver of the sheep. A whole tour awaits them.

The eggs leave their host by the excrements. They are found then outside, where they will await favorable conditions to continue their development. After one period of ripening, they hatch to let leave a tiny ciliée larva: the larva miracidium . This larva will move in the search of its first intermediate host (a gastropodous mollusc of the kind Limnée) the meeting is supported by a phenomenon of Chimiotactisme (capacity of miracidium has to detect chemical substances present in the Mucus of the gastropod). In the body of the Mollusc, the larva will multiply in an asexual way while passing by the stages Sporocyste then redia before arising in the form of cercaire . These cercaires swims then until being fixed on the elements of vegetation which they reach, from where they are enkystent in the form of métacercaire in waiting to be introduced by their final host inside whose the development will be completed on the level of the bile ducts of the liver.

General information

The fasciolose is a disease parasitic affecting more particularly the ruminants and characterized by the development in the bile ducts and hepatic fabric, of trematodes of the species Fasciola hepatica.

Affected species

The Ovine S, and to a lesser extent the Bovins are the species most often reached. However, the fasciolose can develop at other animal species like porcine, the equine ones, léporidés, the wild ruminants and the coypu. It can, much more rarely, to affect the human ones.

Geographical distribution

Cosmopolitan parasite met very frequently in all the moderate zones of Europe, North America and the South, and of Africa. The fasciolose is more widespread in the wet areas. In the tropical climates, other species are observed like Fasciola gigantica and Fasciola huski .

Importance

In the ruminants, the fasciolose revêt a great importance on the economic plan because it causes delays of growth, falls of the lacteous production, seizures at the slaughter-house and sometimes of mortalities.

In the horse its incidence is difficult to appreciate in the absence of precise epidemiological studies, of the difficulty of its diagnosis like by a not very evocative symptomatology.

At the human being the form " subite" is observed following the infected cress ingestion.

The forms latent and sudden are known in groups which nourish infected animal liver.

Because of difficulty of measuring the incidences of the parasite on the Humeur S the Prévalence of the latent form at the man is not known.

Biology

The complete cycle of development is about 6 months (3 months of exogenic cycle of egg to the métacercaires and 3 months of endogenous cycle of the ingestion of the métacercaires to the presence of adult ditches in the bile ducts).

Form adult

The adults of Fasciola hepatica live mainly in the bile ducts and are hermaphrodites (presence of testicles and an ovary at the same individual). They measure 2 to 3 cm length on 8 to 13 mm broad. Their body covered with a pseudocuticule is flattened, Foliacé (from where the name of Fasciola), of pale color brown, oval form with a more frayed former end: the cephalic cone and a widening scapular. A oral suction cup allows the food and a ventral or fixing suction cup allows fixing. They are hematophagous and nourish blood of the capillaries of the wall of the bile ducts. An adult ditch can absorb 0.2 ml of blood per day. The adults can survive several months in the bile ducts. Fecundation is done by ventro-ventral coupling between two individuals or autofecondation; the seminal receptacle stores the sperm which joined the ovary, then the ovocytes maturent while crossing the long uterus before being expelled in the form of eggs.

Eggs

The eggs (140 × |80|µm) is ovoid, covers, of yellowish color with granulous and homogeneous contents. Their elimination in the external medium is made in an irregular way according to the rate/rhythm of biliary drainings (of: 3000 with: 4000 eggs can be eliminated daily by an adult). Generally the egg undergoes a first embryonic development before being eliminated. The eggs of Fasciola hepatica resist little of time the desiccation or freezing, but can survive up to 1 or 2 years in a cold and wet environment.

Embryonic phase

In the external medium, a Embryo cilié, miracidium, develops in egg and in fate at the end of a very variable amount of time (3 to 6 weeks). This miracidium, of triangular form (measuring 130 µm length), stroke in the search of an intermediate host, who is always a Mollusque amphibious Gastéropode and primarily the truncated Limnée ( Lymnaea truncatula ). It penetrates then in the respiratory cavity of the Mollusque and transforms into a called irregular mass sporocyst (300 µm diameter). The sporocyst gives rise to organizations provided with a digestive tract called rediae.

Rediae

The rediae invade the hepatopancreas of mollusc, develop to reach a size from 1,3 to 1,6 mm length, and, according to the climatic conditions, give other rediae to with it (or rediae girls).

Each redia gives rise to a score of particular organizations: the cercaires . They are organizations equipped with a digestive tract, two suction cups and a tail. The cercaires (one can count some until: 4,000 in same limnée) are eliminated by limnée when the external medium is particularly wet. Very quickly the cercaires lose their tail, are enkystent on an immersed plant and are transformed into métacercaires (200 µm). On the immersed plants or a wet meadow their survival can last several months (up to 1 year), on the other hand they are quickly destroyed by a hot and dry climate. The infestation of the animals is done by ingestion of plants carrying métacercaires or same water containing these métacercaires. The cysts thus introduced are dissolved in the intestine and release from the immature ditches which migrate of the intestine towards the hepatic parenchyma (in less than one week) while passing by the cavity péritonéale. The young ditches histophages migrate through the hepatic parenchyma while increasing by size and gain the bile ducts into 7 to 8 weeks. In a few weeks these young ditches become adult and acquire their sexual maturity.

References

  • C. Drunk, C. Boulard, D. Levieux, J. Barnouin and E. Plate, Experimental equine fascioliasis: evolution off serologic, enzymatic and parasitic parameters , Ass. Rech. Vet. , year 1989, vol. 20 (3), pp.295-307
  • D. and A. Levieux, C. Magus and A. Venien, Early immunodiagnosis off bovine fascioliasis using the specific antigen f2 in have passivates hemagglutination test . Vet. Parasitol. , year 1992, vol. 44 (1-2), pp.77-86
  • J. Bussiéras and R. Chermette, Parasitologie Veterinary surgeon: Helminthology , ENVA, 1995.

External bond

  • the ditch on the site of the University of Cambridge

Random links:Waldstatt | Matonge (Kinshasa) | Candida albicans | Balfour Mount | Michele Ray-Gavras | John_Stamos