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.
Molecular Biology and Genetics
Barcode data: Fasciola gigantica
There are 14 barcode sequences available from BOLD and GenBank. 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
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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