Bovis ISSN 2398-2993

Fasciola hepatica: the parasite

Contributor(s): Rob Kelly , Andrew Forbes

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Introduction

Classification

Taxonomy

  • Trematoda; Fasciolidae; Fasciola hepatica.

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.
  • Adult and juvenile migratory stages of the parasite contribute to disease in cattle.
  • Fasciolosis, was first described in sheep, in the 13th century.
    • Similar findings in cattle were first described in the 17th century although disease in cattle is more associated with chronic infections.
    • The intermediate host stages were not discovered until the 19th century.
  • Herbivorous species can be infected with Fasciola hepatica.
    • These include ruminants such as cattle, buffalo, sheep and goats.
    • Fasciolosis also occurs in some other domestic species such as swine and horses and in wildlife, notably rabbits, hares and deer
    • Man may also be affected in certain regions.

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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.
    • Such stages can over winter at pasture and become infective when temperatures increase >10oC.
  • Presence of the intermediate snail hosts are vital for development and transmission of F. hepatica.
    • Fresh water mud snails (Lymnaeidae) are the intermediate hosts of F. hepatica worldwide.
    • Galba truncatula (the dwarf pond snail) is the most common snail intermediate host in the UK and most of Europe.
    • Other species of snail host have localized importance in other countries.
  • Lymnaeidae, including Galba truncatula, inhabit lowland and areas below ~3000m above sea level.
  • They are mainly found around marginal fresh water bodies such as ponds, steams, rivers, swamps . In addition to temporary bodies of water such as puddles, flooded pasture and even hoof prints in muddy ground .
  • Risk of disease, due to increased parasitic burden, will vary from year dependent upon climatic conditions.

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 G. trucatula
  • Miracidia penetrate the snail intermediate host for asexual multiplication through sporocyst, redia to thousands of cercariae.
  • Cercariae exit the snail into the environment and rapidly attach to herbage and encyst into metacercariae; 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 faeces where they can be detected.
  • In total the pre-patent period (PPP) in cattle is 10-12 weeks, in temperate climates, and 4-7 weeks in the obligate snail intermediate host.

Transmission

  • Sheep, and to a lesser extent goats, can be important in transmission of F. hepatica to cattle.
  • Small ruminants can also suffer from clinical fasciolosis.
    • Some species were thought of as aberrant hosts such as horses and wild ruminants.
    • Clinical disease is increasingly being appreciated in equids although their epidemiological importance to cattle is likely minimal. 
  • In the UK, along with much of Northern and Western Europe, risk period for cattle is later summer early autumn for clinical and subclinical disease.
  • Warmer southern Europe and other countries may have less seasonal exposure to F. hepatica with infections occurring all year round depending upon suitable environmental conditions.
  • Primary transmission can occur with eggs being shed on pasture, hatching to miracidia to infect snails, to release of cercariae and form metacercariae on herbage in one grazing season from spring to autumn (May to October) in the UK.  Although disease is not seen until winter or early spring due to the 10-12 week development from juveniles to adults within the definitive host.
  • Peak numbers of metacercariae are found at pasture between August-October although they can be present on pasture all year round.
  • Eggs can survive on pasture over the winter in the UK to hatch and infect snails the following spring.
  • Intermediate stages can also survive whilst the snail host is hibernating over the winter months for reactivation the following spring.
  • 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.
  • Spreading slurry, from infected cattle, can contaminate pasture with F. hepatica eggs that can establish infection if a suitable intermediate host is present.  
  • Metacercariae can survive for short periods on preserved forage and be infective to cattle.

Pathological effects

  • Extent of pathological damage caused by F. hepatica 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 hemorrhage and inflammation of the peritoneal cavity.  
  • Juveniles migrate, once penetrated the hepatic capsule, via secreting 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 migrated to the bile ducts adults feeding causing cholangitis and 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. Furthermore 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.

Other Host Effects

  • Cattle co-infected with F. hepatica have been shown to be more susceptible to other pathogens. Such as Salmonella dublin Salmonella spp and Clostridium novyii Clostridium spp.
  • Fasciola hepatica co-infections have also been demonstrated to affect diagnosis of Mycobacterium bovis Mycobacterium bovis infection in cattle.
    • Using either the single intradermal skin test (SCITT) or gamma-interferon assay.
    • Recently it has also been demonstrated that co-infection might also affect development tubercle pathology with M. bovis infection.

Control

Control via animal

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

Control via chemotherapies

  • Triclabendazole Triclabendazole will treat early immature (~2 weeks) and adult stages of F. hepatica.
  • Closantel Closantel and nitroxynil will treat older intermediate stages and adults of F. hepatica.
  • Albendazole, clorsulon and oxyclozanide will treat adult stages of F. hepatica only.
  • Anthelmintic resistance is less of a problem with cattle due to less intensive use than in sheep.
  • Triclabendazole resistance in cattle has been reported in Scotland and the Netherlands.
    • Although the extent and impact of triclabendazole resistance is still yet to be fully quanitifed, control practices that safeguard the anthelmintic efficacy are imperative. One Health
  • 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. hepatica infection. 
  • Consider the management group being treated in respect to meat and milk withholds.
  • Avoid use of combination anthelmintic preparations for F. hepatica 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.
  • In winter, when housing stock, dosing to target adult stages maybe appropriate (timing dependent upon anthelmintic used).
    • This will assist with reducing pasture contamination the following spring, when turned out.
  • Where heavy pasture contamination occurs in spring/ summer consider targeted treatment to minimise pasture contamination.
  • Once treated may need to retreat 6 - 12 weeks later if cattle are kept on same pasture.
  • Regular diagnostic surveillance will assess overall herd problem and highlight if anthelmintic treatments are required.

Control via environment

  • Drainage and/or fencing off of snail habitats pasture, such as water logged areas of fields, can be useful for control of transmission.  
  • Disease forecasting systems are in place in the UK and other countries to report the seasonal risk of fasciolosis and are useful to tailor control strategies.
  • Farm 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.
  • Cattle have a higher resistance to F. hepatica infections than sheep. Although even previously exposed cattle can be re-infected.
  • Trials on F. hepatica cathepsin protease based vaccines have shown promise; being able to produce ~50% protection in field challenge studies.

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.
  • Molluscocides, such as copper sulphate, have previously been used, on pasture, to control snail populations. However, they have fallen out if favour due to their environmental impacts.

Diagnosis

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Moazeni M & Ahmadi A (2016) Controversial aspects of the life cycle of Fasciola hepatica. Exp parasitol 169, 81–89 PubMed.
  • Mazeri S, Sargison N, Kelly R F, Bronsvoort B M & de C Handel I (2016) Evaluation of the performance of five diagnostic tests for Fasciola hepatica infection in naturally infected cattle using a Bayesian no gold standard approach. PLoS One 11, PubMed.
  • Howell A, Baylis M, Smith R, Pinchbeck G & Williams D (2015) Epidemiology and impact of Fasciola hepatica exposure in high-yielding dairy herds. Prev vet med 121, 41–8 PubMed.
  • Knubben-Schweizer G & Torgerson P R (2015) Bovine fasciolosis: Control strategies based on the location of Galba truncatula habitats on farms. Vet parasitol 208, 77–83 PubMed.
  • 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.
  • McCann C M, Baylis M & Williams D J L (2010) The development of linear regression models using environmental variables to explain the spatial distribution of Fasciola hepatica infection in dairy herds in England and Wales. Int J parasitol 40, 1021–8 PubMed.
  • Golden O, Flynn R J, Read C, Sekiya M, Donnelly S M et al (2010) Protection of cattle against a natural infection of Fasciola hepatica by vaccination with recombinant cathepsin L1 (rFhCL1). Vaccine 28, 5551–5557 PubMed.
  • Charlier J, De Meulemeester L, Claerebout E, Williams D & Vercruysse J (2008) Qualitative and quantitative evaluation of coprological and serological techniques for the diagnosis of fasciolosis in cattle. Vet parasitol 153, 44–51 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.
  • Molloy J B, Anderson G R, Fletcher T I, Landmann J & Knight B C (2005) Evaluation of a commercially available enzyme-linked immunosorbent assay for detecting antibodies to Fasciola hepatica and Fasciola gigantica in cattle, sheep and buffaloes in Australia. Vet Parasitol 130 pp 207–212. 
  • Opara K N (2005) Population Dynamics of Fasciola gigantica in Cattle Slaughtered in Uyo , Nigeria. Parasitology 37, pp 363–368.
  • Molina E C, Gonzaga E A, Sinolinding E O, Lumbao L A, Peralta A A et al (2005) Differences in Susceptibility between Cattle and Swamp Buffaloes to Infection with Fasciola gigantica. Trop Anim Health Prod 37, pp 611–616.
  • Piedrafita D, Raadsma H W, Prowse R & Spithill T W (2004) Immunology of the host–parasite relationship in fasciolosis (Fasciola hepatica and Fasciola gigantica). Can J Zool 82, pp 233–250.
  • Mas-coma S (2003) Human fasciolosis: Epidemiological patterns in human endemic areas of South America, Africa and Asia. Europe, 1–11 PubMed.
  • Wamae L W, Hammond J A, Harrison L J & Onyango-Abuje J A (1998) Comparison of production losses caused by chronic Fasciola gigantica infection in yearling Friesian and Boran cattle. Trop Anim Health Prod 30, pp 23–30.
  • Schillhorn van Veen T W (1980) Fascioliasis (Fasciola gigantica) in West Africa: a review. Vet Bull 50, pp 529–533. Pract 20, 415–427.
  • Offer J E, Logue D N, Roberts D J (1997) The effect of protein source on lameness and solear lesion formation in dairy cattle. Anim. Sci 65, pp 143–149.
  • Nocek J E (1997) Bovine acidosis: Implications on laminitis. J. Dairy Sci 80, pp 1005–1028.
  • Livesey C, Metcalf J, Marsh C, Johnston A & May S (1997) Comparison of high starch and high fibre diets and the development of subclinical laminitis syndrome in dairy heifers. Br. Soc. Anim. Sci. Br. Soc. Anim. Sci 96, pp 96.
  • Boosman R, Nemeth F & Gruys E (1991) Bovine laminitis: clinical aspects, pathology and pathogenesis with reference to acute equine laminitis. Vet. Q 13, pp 163.
  • Bazeley K & Pinsent P J N (1984) Preliminary-Observations on a Series of Outbreaks of Acute Laminitis in Dairy-Cattle. Vet. Rec 115, pp 619–622.
  • Andersson L (1981) An Attempt to Induce Laminitis in Cows by Intra-Ruminal Infusion of Lactic-Acid. Acta Vet. Scand 22, pp 140–142.
  • Anderson L & Bergman A (1980) Pathology of bovine laminitis especially as regards vascular lesions. Acta Vet. Scand 21, pp 559–566.
  • Rowcliffe S A & Ollerenshaw C B (1960) Observations on the bionomics of the egg of Fasciola hepatica. Ann trop med parasitol 54, 172–81 PubMed.

Other sources of information

  • Control of Worms Sustainably (2013) COWS technical manual: Control of liver and rumen fluke in cattle.
  • Andrews A H, Blowey R W, Boyd H & Eddy R G (2004) Bovine medicine: diseases and husbandry of cattle. 2nd edn. Oxford.
  • Dalton J P (ed) (1999) Fasciolosis. 1st edn. CABI Publishing, Oxon, UK.

Organisation(s)

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

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