Bovis ISSN 2398-2993

Fasciola gigantica: the parasite

Synonym(s): large liver fluke

Contributor(s): Rob Kelly, Andrew Forbes

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Introduction

Classification

Taxonomy

  • Trematoda; Fasciolidae; Fasciola gigantica.

Etymology

  • There are two species of Fasciola that infect cattle:
    • Fasciola hepatica in temperate climates
    • Fasciola gigantica mainly found in tropical climates, such as sub-Saharan Africa.
  • Species distribution can overlap as it is governed by the presence of snail intermediate host species that are integral to Fasciola species life cycles.
  • Losses in production are related to the Fasciola species complex lifecycle and subsequent disease termed fasciolosis.
  • Ruminant infections account for £2.5 billion of production losses per annum globally with the impact specifically on F. gigantica infected animals undefined.
  • Adult and juvenile migratory stages of the parasite contribute to disease in cattle.
  • Fasciolosis, was first described also the 13th century in sheep.
    • Similar findings in cattle were first described in the 17th century, although disease in cattle is more associated with chronic infections.
    • However the intermediate host stages were not discovered until 19th century with the complete life cycle in sheep elucidated in 1926.
  • Ruminants such as cattle, buffalo, sheep and goats are affected by infection.  Man may also be affected in certain areas.

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Clinical Effects

Epidemiology

Habitat

  • In general resting environmental stages, such as the eggs and metacercariae, require moist wet environments to survive.
  • Presence of the intermediate snail hosts are vital for development and transmission of F. gigantica.
  • Fresh water aquatic snails, of the Radix auricularia complex, are the intermediate hosts of F. gigantica.
    • Specific species of snail host have localized importance on African and Asian continents.
  • Radix intermediate host species inhabit streams, water irrigation channels, rice paddies and edges of lakes but their range can also increase when flooding occurs
  • Risk of disease, due to increased parasitic burden, will vary from year dependent upon climatic conditions.
    • Radix species can survive a period of desiccation to enable persistence through wet and dry seasons in tropical regions.

Lifecycle

  • Eggs are passed in the feces onto pasture and under the correct conditions develop into miracidia.
  • Miracidia are highly motile and locate obligate snail intermediate host such as R. natalensis or R. rufescens
  • Miracidia penetrate the snail intermediate host for asexual multiplication through sporocyst, redia to thousands of cercariae.
  • Cercariae exit the snail into the environment to form encysted metacercariae.  
  • Metacercariae mainly float within the water or attach to herbage.
  • Metacercariae are the infective form to definitive hosts.
  • When cattle are grazing they ingest metacercariae which excyst in the lumen of the small intestine and penetrate into the abdomen to migrate towards the liver.
  • Juveniles penetrate the surface of the liver and migrate through the liver parenchyma to the bile ducts.
  • Maturation occurs in the bile ducts, where the adults feed, and sexually reproduce to produce eggs.
  • Eggs are then passed intermittently from the bile ducts, via the gall bladder, into the small intestinal lumen into the feces where they can be detected.
  • In total the pre-patent period (PPP) in cattle is 12-16 weeks in tropical and sub-tropical climates.

Transmission

  • Fasciola gigantica mainly infects cattle, buffalos and wild ruminants as well as man.
  • The parasite can transmit to sheep and goats although the parasite is thought to be better adapted to infection in larger ruminants.
    • Indonesian fat tailed sheep appear to be resistant to F. gigantica infections.
    • There have been fewer studies investigating the definitive host species of F gigantica compared to F. hepatica.
  • Passage of eggs onto pasture from definitive hosts is dependent upon parasite burden, frequency of eggs release from the gall bladder and composition of fecal matter in the host.
  • Due to the tropical/sub-tropical climate preferred by F. gigantica; infection can occur all year round depending upon suitable environmental conditions for transmission. Hence it is likely cattle are exposure frequently throughout the year.
  • In areas where the conditions of dry season limit transmission stages can survive within the intermediate snail host. Along with eggs and metacercariae surviving within water bodies.
  • Metacercariae can be dispersed by currents in water bodies beyond where snail habitat is present to infect definitive host species.
  • Metacercariae can survive for short periods on preserved forage and be infective to cattle.

Pathological effects

  • Extent of pathological damage caused by F. gigantica infection, and subsequent degree of clinical disease, is dependent upon intensity of infection and parasite burden.
Subsequently chronic, rather than acute, disease is reported in cattle.
  • Upon penetration of the intestinal wall there is mild haemorrhage and inflammation of the peritoneal cavity.  
  • Juveniles migrate, once they have penetrated the hepatic capsule, via secreting a mix of cathepsin proteases to enable lysis of tissue and host immune evasion.
    • During these stages profuse hemorrhage and inflammation occurs.
    • Migratory tracts that can be seen grossly as red-white scars through the liver.
    • Microscopically, these tracts are composed of macrophages, eosinophils and other inflammatory cells.
  • Migratory tracts develop into fibrotic tracts composed of connective tissue . Resulting in interstitial hepatitis, fibrosis and cirrhosis of the liver.
  • With heavy burdens the bovine liver may also shrink in size.
  • Once in the bile ducts, the feeding adults cause cholangitis.  Over time this results in chronic inflammatory changes.
    • In cattle such inflammation results in calcification of the bile ducts also known is “pipe-steam” liver .
  • Chronic inflammation can result in bacterial proliferation and abscess formation.
  • Chronic inflammation can result in parasites being unable to feed and may limit the extent of parasite burden over time.
  • In some cases, especially where cattle have been exposed to light burdens, the liver may regenerate where no re-infection occurs.
    • In tropical and sub-tropical climates this would require cattle avoiding infected pasture for years.

Other Host Effects

  • Fasciola gigantica co-infections have also been demonstrated to affect diagnosis of Mycobacterium bovis Mycobacterium bovis infection in cattle similarly to F. hepatica Fasciola hepatica.

Control

Control via animal

  • Identify which cattle are at risk of disease through post mortem feedback or ante-mortem diagnostics.
  • Brought in ruminants may bring in F. gigantica infection to a negative herd where suitable snail host and environmental conditions exist.
  • Quarantine, test and treat bought in animals appropriately.
  • Negative herds are unlikely in tropical and sub-tropical environments.

Control via chemotherapies

  • Triclabendazole Triclabendazole will treat early immature (~2 weeks) and adult stages of F. gigantica.
  • Closantel Closantel and nitroxynil will treat older intermediate stages and adults of F. gigantica.
  • Albendazole, clorsulon and oxyclozanide will treat adult stages of F. gigantica only.
  • Anthelmintic resistance One health has been minimally reported with F. gigantica infections likely due to less frequent use of anthelmintics where F. gigantica is endemic.
    • It is likely that similar anthelmintic selection pressures associated with F. hepatica resistance would select for resistance in F. gigantica.
Refer to anthelmintic data sheets for correct dose rates for Fasciola developmental stages within cattle.
  • Weigh tapes and scales can be useful for accurately dosing cattle their weight to avoid under dosing and selecting for anthelmintic resistance in herds.
  • Consider the time of year when using treatments and which anthelmintic will be affective against which stages of F. gigantica infection.
  • Consider the management group being treated in respect to meat and milk withholds.
  • Avoid use of combination anthelmintic preparations for F. gigantica infection unless an adjunct infective treatment is also required. 
  • Targeted treatments are important to not overuse anthelmintic and select for anthelmintic resistance.
    • Specific control measures require a tailored approach to the farming system and environment within the tropics.
  • If cattle are housed or confined, such as during the dry season, dosing to target adult stages maybe appropriate (timing dependent upon anthelmintic used).
  • Cattle that are at pasture all the time, such as nomadic herds, might use targeted treatment when grazing on heavily infected pasture during the dry season.
  • Once treated may need to retreat 10- 16 weeks later if cattle are kept on same pasture.
  • Ideally regular diagnostic surveillance will assess overall herd problem and highlight if anthelmintic treatments are required.

Control via environment

  • Avoidance, drainage and/or fencing off of snail habitats pasture, such as contaminated watercourses, can be useful for control of transmission. 
  • Cattle drinking from faster moving and deeper water are less likely to be exposed to F. gigantica infections.
    • Although drinking from such areas may increase the exposure to other parasites in tropical regions where intermediate hosts are associated with such environmental conditions. Including certain Schistosoma, Onchocerca and Trypanosoma species that also have zoonotic implications.
  • Farm or pasture walks are very useful for the clinician to identify areas of potential snail habitat with the farmer to tailor environmental control measures to the individual system.

Vaccination

  • None currently available.

Other countermeasures

  • If resistance to an anthelmintic is suspected investigate using fecal egg count reduction tests (FECRT) protocols.
  • Where anthelmintic resistance is reported in sheep that are co-grazed with cattle similar anthelmintic precautions should be applied.
  • Mollucosides on pasture have previously been used to control intermediate host species at pasture such as copper sulphate. However they are not currently used due to their damage to the environment, local ecosystems and livestock grazing.

Diagnosis

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Khan M K, Sajid M S, Riaz H, Ahmad N E, He L, Shahzad M, Hussain A, Khan M N, Iqbal Z & Zhao J (2013) The global burden of fasciolosis in domestic animals with an outlook on the contribution of new approaches for diagnosis and control. Parasitol res 112, 2421–30 PubMed.
  • Pleasance J, Raadsma H W, Estuningsih S E, Widjajanti S, Meeusen E et al (2011) Innate and adaptive resistance of Indonesian Thin Tail sheep to liver fluke: A comparative analysis of Fasciola gigantica and Fasciola hepatica infection. Vet parasitol 178, 264–272 PubMed.
  • Valero M A, Perez-Crespo I, Periago M V, Khoubbane M & Mas-Coma S (2009) Fluke egg characteristics for the diagnosis of human and animal fascioliasis by Fasciola hepatica and F. gigantica. Acta trop 111, 150–159 PubMed.
  • Kumar N, Ghosh S & Gupta S C (2008) Early detection of Fasciola gigantica infection in buffaloes by enzyme-linked immunosorbent assay and dot enzyme-linked immunosorbent assay. Parasitol res 103, 141–150 PubMed.
  • Walker S M, Makundi E, Namuba F V, Kassuku A, Keyyu J et al (2008) The distribution of Fasciola hepatica and Fasciola gigantica within southern Tanzania--constraints associated with the intermediate host. Parasitology 135, 495–503 PubMed.
  • Raadsma H W, Kingsford N M, Suharyanta, Spithill T W & Piedrafita D (2008) Host responses during experimental infection with Fasciola gigantica and Fasciola hepatica in Merino sheep: II. Development of a predictive index for Fasciola gigantica worm burden. Vet parasitol 154, 250–261 PubMed.
  • Keyyu J D, Kyvsgaard N C, Monrad J & Kassuku A A (2008) Effectiveness of strategic anthelmintic treatments in the control of gastrointestinal nematodes and Fasciola gigantica in cattle in Iringa region, Tanzania. Trop anim health prod 41, 25–33 PubMed.
  • McGarry J W, Ortiz P L, Hodgkinson J E, Goreish I, Williams D J L (2007) PCR-based differentiation of Fasciola species (Trematoda: Fasciolidae), using primers based on RAPD-derived sequences. Ann trop med parasitol 101, 415–21 PubMed.
  • Suhardono, Roberts J A & Copeman D B (2006) The effect of temperature and humidity on longevity of metacercariae of Fasciola gigantica. Trop anim health prod 38, 371–377 PubMed.
  • Roberts J A & Copeman D B (2006) Distribution of Metacercariae of Fasciola gigantica on rice straw. Trop anim health prod 38, 117–119 PubMed.
  • Mungube E O, Bauni S M, Tenhagen B, Wamae L W, Nginyi J M et al (2006) The prevalence and economic significance of Fasciola gigantica and Stilesia hepatica in slaughtered animals in the semi-arid coastal Kenya. Trop anim health prod 38, 475–483 PubMed.

Other sources of information

  • Dalton J P (ed) (1999) Fasciolosis. 1st edn. CABI Publishing, Oxon, UK.
  • Hammond I A & Sewell M M H (1990) Diseases caused by helminths. In: Handbook on animal diseases in the tropics. London: Bailliere Tindall. pp 105–160.

Organisation(s)

  • Royal (Dick) School of Veterinary Studies, University of Edinburgh, UK.

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