liver fluke

1. Any of several parasitic trematode worms, especially Clonorchis sinensis, that infest the liver of various animals, including humans.
2. Infestation with such parasitic worms. Also called rot.

Fasciola hepatica

ORDER

Echinostomida

FAMILY

Fasciolidae

TAXONOMY

Fasciola hepatica Linnaeus, 1758, "in aquis dulcibus ad radices lapidum, inque hepate pecorum. Diss. de Ovibus;" Europe.

OTHER COMMON NAMES

English: Sheep liver fluke; French: Grande douve du foie, douve du foie de mouton; German: Großer Leberegel.

PHYSICAL CHARACTERISTICS

Adult liver flukes may reach 1.7–2.2 in (4–5 cm) in length and 0.6 in (1.5 cm) wide. They are typically about 1.3 in (3 cm) long, 0.4 in (1 cm) wide, and have a spiny tegument. They taper toward the rear. The front end bears an oral sucker and a cone-shaped tip. The sucker on the fluke's ventral (lower) surface is larger than the oral sucker. The ventral sucker is about a third of the body length behind the oral sucker. The branched ovary is situated behind and to the side of the ventral sucker about a third of the way back in the body. The testes are also branched and extend throughout the body behind the ovary.

DISTRIBUTION

Worldwide, but found most often in Europe and Latin America in habitats congenial to their freshwater snail and definitive hosts.

HABITAT

Liver flukes are found in swampy, generally wet freshwater areas inhabited by snails, especially of the species Lymnaea truncatula, Stagnicola bulimoides, and Fossaria modicella. Snails are their sole intermediate host. The definitive hosts of this fluke include grazing herbivores (in the bile ducts) primarily, including sheep and cattle, but also dogs, cats, rabbits, and humans.

BEHAVIOR

The eggs, deposited in the environment in the definitive host's feces, hatch in freshwater areas, usually within about 10 days, longer if temperatures are cool. They have been known to survive in particularly cold water for several years. The embryos develop into miracidia, which quickly swim to and penetrate the soft tissue of snails. Miracidia can survive only 24 hours in the free-living state. Sporocysts form and produce first-generation rediae, which in turn produce second-generation rediae and eventually numerous cercariae. The cercariae live in the snail for 4–8 weeks, then exit and swim to vegetation lying just below the water line. There, they drop their tails and encyst. Passing herbivores become infected when they eat the vegetation, often grass. Humans typically become infected by drinking water containing flukes or by eating vegetation such as watercress. The flukes travel to the abdominal cavity in the first 24 hours, then to the liver over the next few days. Research indicates that immature flukes are able to orient during their migration from the duodenum (the first section of the small intestine) toward the liver. Within six to eight weeks, they reach the bile ducts, sometimes spreading to the lungs, where they mature and lay eggs. The eggs are then carried to the duodenum and pass into the feces.

FEEDING ECOLOGY AND DIET

This parasitic digenetic fluke has two hosts: Lymnaea species as the intermediate host, and wild or domesticated ruminants as the definitive host. Humans may become secondary hosts. The fluke feeds on bile duct lining, causing calcification of the duct.

REPRODUCTIVE BIOLOGY

The tan or yellow eggs are about 0.0048–0.006 in (120–150 µm) long and 0.0025–0.0035 in (65–90 µm) wide. In warm water (78.8°F or 26°C), they develop into miracidia in less than two weeks. The miracidia are ciliated, and somewhat triangular in shape with the front end being broader than the rear. The front end also has a noticeable slender outgrowth with two eyespots behind it. The cercariae, which range from 0.0098–0.013 in (250–350 µm) long, resemble tadpoles in shape with a bulbous anterior end and long tail making up about two-thirds of the overall length. In artificial laboratory conditions, adult flukes have been known to survive as long as 11 years.

CONSERVATION STATUS

Not listed by IUCN.

SIGNIFICANCE TO HUMANS

Infected humans may develop symptoms ranging from skin inflammation to pneumonia. Fluke infection can result in massive hemorrhages in horses, a reduction of milk production in dairy cattle, and mortality in sheep. Sheep mortality is often caused by bacterium Clostridium novyi, which thrives on the infected livers of sheep.

The noun has one meaning:

Meaning #1: flatworm parasitic in liver and bile ducts of domestic animals and humans
  Synonym: Fasciola hepatica

Fasciola hepatica

Liver flukes are a polyphyletic group of trematodes (phylum Platyhelminthes). Adults of liver flukes are localized in the liver of various mammals, including humans. These flatworms can occur in bile ducts, gallbladder, and liver parenchyma. They feed on blood. Adult flukes produce eggs which are passed into the intestine.

Examples include:

• Clonorchis sinensis (the "Chinese liver fluke" or the "Oriental liver fluke")
• Dicrocoelium dendriticum (lancet liver fluke)
• Dicrocoelium hospes
• Fasciola hepatica (the "sheep liver fluke")
• Fascioloides magna (the "giant liver fluke")
• Fasciola gigantica
• Fasciola jacksoni
• Metorchis conjunctus
• Metorchis albidus
• Protofasciola robusta
• Parafasciolopsis fasciomorphae
• Opisthorchis viverrini (Southeast Asian liver fluke)
• Opisthorchis felineus (cat liver fluke).
• Opisthorchis guayaquilensis

See also

• Fascioliasis

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v • d • e Infectious diseases · Parasitic disease: helminthiases (B65-B83, 120-129) Flatworm/ platyhelminth Fluke/trematode (Trematode infection) Blood fluke Schistosoma mansoni/japonicum/mekongi/haematobium (Schistosomiasis) · Trichobilharzia regenti (Swimmer's itch) Liver fluke Clonorchis sinensis (Clonorchiasis) · Fasciola hepatica/gigantica (Fascioliasis) · Opisthorchis Lung fluke Paragonimus westermani (Paragonimiasis) Intestinal fluke Fasciolopsis buski (Fasciolopsiasis) Cestoda (Tapeworm infection) Cyclophyllidea Echinococcus granulosus/Echinococcus multilocularis (Echinococcosis) · Taenia saginata (beef)/Taenia solium (pork) (Taeniasis/Cysticercosis) · Hymenolepis nana/Hymenolepis diminuta (Hymenolepiasis) Pseudophyllidea Diphyllobothrium latum (Diphyllobothriasis) · Spirometra erinaceieuropaei (Sparganosis) · Diphyllobothrium mansonoides (Sparganosis) Roundworm/nematode (Nematode infection) Secernentea Spirurida Camallanina Dracunculus medinensis (Dracunculiasis) Spirurina Filarioidea (Filariasis) Onchocerca volvulus (Onchocerciasis) · Loa loa (Loa loa filariasis) · Mansonella (Mansonelliasis) · Dirofilaria repens (Dirofilariasis) Wuchereria bancrofti · Brugia malayi · Brugia timori Thelazioidea Gnathostoma (Gnathostomiasis) Strongylida (hookworm) Ancylostoma duodenale/Ancylostoma braziliense (Ancylostomiasis, Cutaneous larva migrans) · Necator americanus (Necatoriasis) · Angiostrongylus cantonensis (Angiostrongyliasis) Ascaridida Ascaris lumbricoides (Ascariasis) · Anisakis (Anisakiasis) · Toxocara canis/Toxocara cati (Visceral larva migrans/Toxocariasis) · Baylisascaris Rhabditida Strongyloides stercoralis (Strongyloidiasis) Oxyurida Enterobius vermicularis (Enterobiasis · Pinworm) Adenophorea Trichinella spiralis (Trichinosis) · Trichuris trichiura (Trichuriasis · Whipworm) · Capillaria philippinensis (Capillariasis) see also drugs

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