The trematodes Fasciola gigantica and Fasciola hepatica (the Sheep Liver Fluke) are parasites of herbivores that can infect humans accidentally, causing a condition known as fascioliasis. Fascioliasis occurs worldwide . Human infections with F. hepatica are found in areas where sheep and cattle are raised, and where humans consume raw watercress (see life cycle), including Europe, the Middle East, and Asia. Infections with F. gigantica have been reported, more rarely, in Asia, Africa, and Hawaii. Fascioliasis in Europe, the Americas, and Oceania involves only F. hepatica, but both F. hepatica and F. gigantica occur in many parts of Africa and Asia and there is evedince that hybridization occurs (Mas-Coma et al. 2005). (Centers for Disease Control Parasites and Health Website)
Immature eggs are discharged in the biliary ducts and in the stool. Eggs become embryonated in water and release miracidia, which invade a suitable snail intermediate host, including snails in the genera Galba, Fossaria and Pseudosuccinea. In the snail, the parasites pass through several developmental stages: sporocyst, redia, and cercaria. The cercariae are released from the snail and encyst as metacercariae on aquatic vegetation or other surfaces. Mammals acquire the infection by eating vegetation containing metacercariae. Humans can become infected by ingesting metacercariae-containing freshwater plants, especially watercress. After ingestion, the metacercariae excyst in the duodenum and migrate through the intestinal wall, the peritoneal cavity, and the liver parenchyma into the biliary ducts, where they develop into adults. In humans, maturation from metacercariae into adult flukes takes approximately 3 to 4 months. The adult flukes (Fasciola hepatica: up to 30 mm by 13 mm; F. gigantica: up to 75 mm) reside in the large biliary ducts of the mammalian host. (Centers for Disease Control Parasites and Health Website)
Two hosts are needed for these parasites to complete their life cycle. The deﬁnitive host range is very broad and includes many herbivorous mammals, including humans. Intermediate hosts are freshwater snail species of the family Lymnaeidae (Gastropoda: Basommatophora). Fasciola hepatica has spread to other continents from Europe through the exportation of European livestock to other continents, where it has adapted to new hosts such as camelids in Africa and South America and marsupials in Australia. This expansion is also related to the geographic expansion of the original European lymnaeid intermediate host species of F. hepatica, G. truncatula, the spread of the American intermediate host species Pseudosuccinea columella, and the parasite's adaptation to lymnaeid species occurring in new areas. The more limited geographic distribution of F. gigantica seems to be related to the weaker diffusion capacity of its intermediate snail hosts, the African Radix natalensis and the European Radix auricularia. Mas-Coma et al. (2005) reviewed the biology, diagnosis, treatment, and epidemiology of fascioliasis.(Mas-Coma et al. 2005 and references therein) Young et al. (2011) reported on a transcriptome analysis of F. gigantica, which should facilitate genetic and physiological studies that could lead to effective interventions against this parasite.
Fasciola gigantica is found in tropical Africa, South and South-east Asia, and the Far East. In the United States F. gigantica is found in Hawaii.
Biogeographic Regions: palearctic (Native ); oriental (Native ); ethiopian (Native )
Fasciola gigantica is leaf-shaped and tapers at both ends. An adult can grow to 75 mm in length. With the use of a scanning electron microscope the surface of F. gigantica appears very rough due to abundant microscopic spines and surface folding. Spines increase in size in their middle section and are smaller on the surface near the suckers. Spikes range from 30 μm to 58 μm and have serrated edges with anywhere from 16 to 20 sharp points. This species has both an oral and ventral sucker for feeding and attaching to the inside of its host. Fasciola gigantica also has three different types of surface papillae which are used as sensory receptors. The eggs of F. gigantica can reach sizes of 0.2 mm in length.
Range length: 25 to 75 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike
The habitat of Fasciola gigantica changes with the stage of its life cycle. Adult F. gigantica live in the liver and bile ducts of its definitive hosts (sheep, cattle, and other grazing ruminant mammals). Eggs shed by adults are located in the intestinal track of mammals and also in the wild. Free swimming cercarias are found in the bodies of fresh water that are in close proximity of its definitive host. Temperatures above 10 degree Celsius are required for the development of the miracidia larvae stage. Miracidia are found in fresh water that contains intermediate snail hosts in the genus Lymnaea. Metacercaria are found encysted on vegetation and in the mammal host once ingested. Inside the snail rediae persist in the digestive gland of the mammal host, known as the hepatopancreas.
Adequate amounts of moisture are also needed, these factors can account for the intensity and prevalence of infection in the definitive hosts. Increased numbers of incidences are seen in the wet season.
Habitat Regions: tropical ; freshwater
Aquatic Biomes: lakes and ponds
Wetlands: marsh ; swamp
When the adult Fasciola are in the bile ducts of a host it obtains a small portion of its nutrients from active bloodsucking. In a day’s time, a single adult fluke can take in about 0.2 ml of blood. There is evidence that adult flukes need around 100 times the amount of glucose than Fasciola receives from active ingestion. Therefore, adult flukes also receive nutrients by absorption of glucose through their tegument. The free-swimming miracidia were once thought to be a non-feeding stage, but it has been shown they metabolize glucose when it is present.
Animal Foods: mammals; blood
Primary Diet: carnivore (Sanguivore )
Fasciola spp. have a negative impact on its definitive host and are capable of causing mortality if infection is severe. Fasciola gigantica parasitizes lymnaeid snails, which are intermediate hosts, and cows, sheep and other ruminants, which are definitive hosts. In some instances humans are also infected.
Ecosystem Impact: parasite
Species Used as Host:
- lymnaeid snails, Lymnaea
- sheep, Caprinae
- cows, Bovinae
- humans, Homo sapiens
A variety of general aquatic predators are known to feed on the free-living stages of Fasciola gigantica, including the miracidia and the cercariae stages.
Life History and Behavior
The time it takes for the shelled embryos of Fasciola gigantica to hatch is rapidly increased in the presence of light. If they are kept in darkness the number of miracidia that make it to the free-swimming stage are greatly reduced. The miracidium have extremely functional eye-spots. This is probably to prevent premature hatching before the embryos have exited the host’s digestive track. The attack of a proteoplytic enzyme protein controls the opening of the operculum which allows the miracidium to exit the shelled embryo. There is evidence that the blue and violet portion of the light spectrum triggers this attack.
Communication Channels: tactile
Perception Channels: visual ; tactile ; chemical
Adult flukes produce eggs that are passed in the host’s feces. In the wild the eggs hatch into miracidia and penetrate a snail host. The miracidia form into saclike sporocysts and multiply into rediae which then develop into cercariae. Free swimming cercariae are shed from snails, they then find aquatic plants, encyst and become metacercariae. Metacercariae cysts wait to be taken up by other ruminant host to repeat the life cycle. In the transmission stage the metacercariae are unknowingly ingested with aquatic plants by humans and grazing mammals. In the mammal host metacercariae excyst in the duodenum. Immature flukes then penetrate the liver and become mature in the biliary track.
The life span for each stage of Fasciola gigantica varies greatly. After being ingested it takes 3-4 month for adult flukes to become mature and begin producing eggs. Adult flukes can live for multiple years in their definitive host. Embryos of Fasciola species are able to persist outside the host for several months. The free-swimming miracidium will die soon after hatching if they do not contact a secondary host. If conditions are favorable metacercaria are able to persist for up to a year once encysted.
Sexually mature adults reside and presumably mate in biliary ducts of their mammalian host.
Fasciola gigantica reproduce sexually as adults and asexually in the other stages of its life cycle. The flukes are in the metacercariae stage before becoming sexual adults. After residing in their mammal host’s duodenum, the metacercariae penetrate the liver and become mature in the biliary track. The adult flukes have both sex organs, but fertilization between adult male and female flukes is the most common source of sexual reproduction. Adult flukes produce eggs that are then passed in the host’s feces.
Key Reproductive Features: sexual ; asexual ; fertilization (Internal )
Non-embryonic eggs are laid within the mammalian host and are passed through to the intestinal tract where they are expelled in the feces.
Parental Investment: no parental involvement
Molecular Biology and Genetics
Barcode data: Fasciola gigantica
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Fasciola gigantica
Public Records: 3
Specimens with Barcodes: 3
Species With Barcodes: 1
US Federal List: no special status
CITES: no special status
State of Michigan List: no special status
Relevance to Humans and Ecosystems
Fasciola spp. cause a disease known as fascioliasis, which can cause significant economic loss when it infects livestock. This parasite reduces the amount of meat that a cow will produce when slaughtered, and leaves the liver inedible. This parasite also reduces milk production and can causes mortality in chronic infections. In some developing countries fascioliasis is the second leading cause of economical loss, costing 10 million dollars annually. Immunization of livestock also adds to the cost of fascioliasis. Few human infections with F. gigantica have been reported but are seen in Asia, Africa, and Hawaii.
Negative Impacts: injures humans (causes disease in humans ); causes or carries domestic animal disease
These are no known positive effects of Fasciola gigantica on humans.
Fasciola gigantica is a parasitic flatworm of the class Trematoda, which causes tropical fascioliasis. It is regarded as one of the most important single platyhelminth infections of ruminants in Asia and Africa. Estimates of infection rates are as high as 80-100% in some countries. The infection is commonly called fasciolosis.
The prevalence of F. gigantica often overlaps with that of Fasciola hepatica, and the two species are so closely related in terms of genetics, behaviour, and morphological and anatomical structures that it is notoriously difficult to distinguish them. Therefore, sophisticated molecular techniques are required to correctly identify and diagnose the infection.
Fasciola gigantica causes outbreaks in tropical areas of southern Asia, Southeast Asia, and Africa. The geographical distribution of F. gigantica overlaps with Fasciola hepatica in many African and Asian countries and sometimes in the same country, although in such cases the ecological requirement of the flukes and their snail host are distinct. Infection is most prevalent in regions with intensive sheep and cattle production. In Egypt F. gigantica has existed in domestic animals since the times of the pharaohs.
The life cycle of Fasciola gigantica is as follows: eggs (transported with feces) → eggs hatch → miracidium → miracidium infect snail intermediate host → (parthenogenesis in 24 hours) sporocyst → redia → daughter redia → cercaria → (gets outside the snail) → metacercaria → infection of the host → adult stage produces eggs.
As with other trematodes, Fasciola develop in a molluscan intermediate host. Species of the freshwater snails from the family Lymnaeidae are well known for their role as intermediate hosts in the life cycle of Fasciola gigantica; however, throughout the years an increasing number of other molluscan intermediate hosts of F. gigantica have been reported. It has been reported that the Lymnaeid intermediate hosts of F. gigantica are distinguishable from those of F. hepatica, both morphologically and as to habitat requirement. The species of Fasciola can become adapted to new intermediate hosts under certain conditions at least based on laboratory trials. The most important intermediate host for F. gigantica is Radix auricularia. However, other species are also known to harbour the fluke including Lymnaea rufescens and Lymnaea acuminata in the Indian Subcontinent; Radix rubiginosa and Radix natalensis in Malaysia and in Africa respectively; and the synonymous Lymnaea cailliaudi in east Africa. Other snails also serve as natural or experimental intermediate such as Austropeplea ollula, Austropeplea viridis, Radix peregra, Radix luteola, Pseudosuccinea columella and Galba truncatula. The Australian Lymnaea tomentosa (host of F. hepatica) was shown to be receptive to miracidia of F. gigantica from East Africa, Malaysia and Indonesia.
The parasite infects cattle and buffalo and can also be seen regionally in goats, sheep, and donkeys.
Infection and Pathogenicity
Infection with Fasciola spp. occurs when metacercariae are accidentally ingested on raw vegetation. The metacercariae exist in the small intestine, and move through the intestinal wall and peritoneal cavity to the liver where adults mature in the biliary ducts of the liver. Eggs are passed through the bile ducts into the intestine where they are then passed in the feces.
Despite the importance to differentiate between the infection by either fasciolid species, due to their distinct epidemiological, pathological and control characteristics, there is, unfortunately, coprological (excretion-related) or immunological diagnosis are difficult. Especially in humans, specific detection by clinical, pathological, coprological or immunological methods are unreliable. Molecular assays are the only promising tools, such as PCR-RFLP assay, and the very rapid loop-mediated isothermal amplification (LAMP).
Triclabendazole is the drug of choice in fasciolosis as it is highly effective against both mature and immature flukes. Artemether has been demonstrated in vitro to equally effective. Though slightly less potent, artesunate is also useful in human fasciolosis.
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