Lapis ISSN 2398-2969

Fasciola hepatica

Contributor(s): David Vella, Ron Rees Davies, Vicki Baldrey

Introduction

Classification

Taxonomy

  • Class: Trematoda. 
  • Family: Fasciolidae.  
  • GenusFasciola.  
  • Specieshepaticagigantica.

Etymology

  • Hepatica: of the liver.

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Clinical Effects

Epidemiology

Habitat

  • Free-living stages of F. hepatica and those within the intermediate host (snail), require environmental moisture (damp soil at neutral or slightly acid pH) and moderate temperatures.  They can also be found on the edges of streams and channels. 
  • Snails that transmit F. gigantica are found in large bodies of water, ie dams, and also slow-moving channels and streams.

Lifecycle

  1. Egg Fasciola hepatica: egg 01.
  2. Miracidium Fasciola hepatica: miracidium.
  3. Larval stages within intermediate host (sporocyst, redia, cercaria) Fasciola hepatica: cercaria.
  4. Metacercaria (encyst on herbage) Fasciola hepatica: metacercariae.
  5. Juvenile flukes in liver parenchyma Fasciola hepatica: migrating liver fluke - histopathology.
  6. Adult flukes in bile ducts .

Transmission

  • Infection is via ingestion of metacercariae encysted on herbage.  
  • Many mammalian species, both farmed and wild, are final hosts of Fasciola spp, and can contaminate pastures. 
  • Any pasture, therefore, in endemic areas, is a potential source of infection.  
  • Water sources may also occasionally be contaminated by "floating metacercariae".

Pathological effects

  • The immune response of rabbits to natural infection is poorly described in the literature, though the response to vaccine antigens has been studied as an experimental model for vaccine use. 
  • In ruminants, infection results in a typical Th2 immune response, with eosinophilia and mastocytosis. 
  • The response to vaccine fractions does seem to be capable of reducing levels of infection. 
  • The relative resistance of rabbits, and other hosts such as pigs and horses, is likely to be due to non-specific defence mechanisms such as a fibrotic response to migrating flukes. 
  • Infection even of resistant hosts such as rabbits can cause destruction of liver tissue and replacement with fibrous tissue. 
  • Many infected rabbits will show little or no pathology:
    • Enlargement and hyperplasia of bile ducts and monolobar fibrosis would be expected. 
    • Compromise of liver function is unlikely due to the relatively small area of tissue likely to be affected in the rabbit. 
    • In humans, who are also relatively resistant hosts, moderate to severe abdominal pain is a common feature of even light infections.

Other Host Effects

  • Low numbers of liver flukes infecting rabbits are unlikely to be pathogenic.

Control

Control via chemotherapies

  • Specific chemotherapy is seldom used following a specific diagnosis in rabbits. 
  • Triclabendazole (Fasinex®) was found to be the most effective drug in experimental rabbit studies.
  • Study results vary on the effectiveness of praziquantel Praziquantel.

Unlicensed for use in the rabbit.

Control via environment

  • Avoid grazing rabbits on areas of wet pasture inhabited by livestock or wild rabbits, or banks of watercourses downstream of such pasture.

Vaccination

  • Vaccination is effective in rabbits at reducing infection levels, and the prospects for the development of vaccines for the control of fascioliasis in ruminants are good, but vaccination of domestic rabbits against natural infestation is not warranted.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Prasad A et al (1999) Studies on the viability of metacercariae of Fasciola giganticaJ Helminthol 73 (2), 163-166 PubMed.
  • Abrous M et al (1998) Morphological variability in Fasciola hepatica eggs in ruminants, rodents and lagomorphs. J Helminthol 72 (4), 313-317 PubMed.
  • El-Sayad M H (1997) Comparative studies on the effect ofbithionol, praziquantel and triclabendazole in rabbits fascioliasis. 1 Parasitological studies. J Egypt Soc Parasitol 27 (1), 131-142 PubMed.
  • Muro A et al (1997) Fasciola hepatica: vaccination of rabbits with native and recombinant antigens related to fatty acid binding proteins. Vet Parasitol 69 (3-4), 219-229 PubMed.
  • Apt W et al (1993) [Prevalence of fascioliasis in humans, horses, pigs, and wild rabbits in 3 Chilean provinces.] Boletin de la Oficina Sanitaria Panamerico 115 (5), 405-414 (English abstract; Article in Spanish) PubMed.
  • Boag B (1985) The incidence of helminth parasites from the wild rabbit Oryctolagus cuniculus (L.) in eastern Scotland. J Helminthol 59 (1), 61-69 PubMed.
  • Duwel D (1980) [The rabbit as a reservoir host of Fasciola hepatica?] Zeitschrift fur Parasitenkunde 63 (2), 137-143 English Abstract; Article in German) PubMed.
  • Bailenger J et al (1965) [Importance of leporides as wild reservoirs in the epidemiology of distomatosis due to Fasciola hepatica and Dicrocoelium dendriticum.] Annales de Parasitologie Humaine et Comparee 40, 51-54 (English Abstract; Article in French) PubMed.

Other sources of information

  • Dalton J P (1999) Fasciolosis. CABI Publishing, Oxford, UK (a most comprehensive and up-to-the minute reference on all aspects of liver fluke and liver fluke disease).

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