Fasciola edit
Fasciola, commonly known as the liver fluke, is a genus of parasitic trematodes. There are two species within the genus Fasciola: Fasciola hepatica and Fasciola gigantica, as well as hybrids between the two species. Both species infect the liver tissue of a wide variety of mammals, including humans, in a condition known as fascioliasis. F. hepatica measures up to 30 mm by 15 mm, while F. gigantica measures up to 75 mm by 15 mm.[1]
Life Cycle edit
Fasciola pass through five phases in their life cycle: egg, miracidium, cercaria, metacercaria, and adult fluke.[1] The eggs are passed in the feces of mammalian hosts and, if they enter freshwater, the eggs embryonate and hatch into miracidia. Miracidia are free-swimmingThe miracidia then infect gastropod intermediate hosts and develop into cercariae, which erupt from the body of the snail host and find and attach to aquatic plants,[2] The cercariae then develop into metacercarial cysts. When these cysts are ingested along with the aquatic plants by a mammalian host, they develop into adult flukes and migrate to the bile ducts.[2] The adults can live for 5-10 years in a mammalian host.[3]
Geographic Distribution edit
Fasciola are widespread and inhabit 70 countries and parts of all continents except for Antarctica. It is most common in areas with sheep and cattle are raised.[1] The regions most impacted by Fasciola are the northern Andes and the Mediterranean region.[4][5]
Animal Hosts edit
The intermediate hosts for Fasciola are gastropods from the family Lymnaeidae, also known as pond snails.[6]
A wide variety of mammals can be definitive hosts for the adult flukes, including pigs, rodents, ruminants, and humans[7]. The most important animal reservoir hosts for human infections are sheep and cattle.[8]
History edit
Fasciola has infected humans since at least Ancient Egypt, as mummies have been found with Fasciola eggs.[9] Cercariae of F. hepatica in a snail and flukes infecting sheep were first observed in 1379 by Jehan De Brie.[5][10] The life cycle and hatching of an egg were first described in 1803 by Zeder.[11]
Prevention and Treatment edit
Fascioliasis is treated with triclabendazole. There is no vaccine for Fasciola currently available.[1] In severe cases of biliary tract obstruction, surgery is an option to remove adult flukes.[3]
The most common way that humans are infected is through the consumption of undercooked vegetables, often watercress, that are contaminated with metacercariae.[12] This is of particular concern in areas where animal waste is used as fertilizer for the cultivation of watercress, as the full life cycle of Fasciola can sustained while contaminating crops intended for human consumption.[5] Additionally, in rare cases, ingestion of the raw liver of an infected animal can lead to infection. This is primarily in the Middle East and is known as halzoun.[10]
One prevention method is to kill off the snail hosts in a water body using molluscicides.[13] Another method is treating entire communities that are at risk for contracting fascioliasis with triclabendazole.[4] This is a time efficient method in impoverished rural communities, as it does not require testing the entire community for fascioliasis.[4]
References edit
- ^ a b c d Prevention, CDC-Centers for Disease Control and (2019-04-16). "CDC - Fasciola - General Information - Frequently Asked Questions (FAQs)". www.cdc.gov. Retrieved 2019-11-14.
- ^ a b Prevention, CDC-Centers for Disease Control and (2019-05-03). "CDC - Fasciola - Biology". www.cdc.gov. Retrieved 2019-11-14.
- ^ a b Prevention, CDC-Centers for Disease Control and (2019-05-24). "CDC - Fasciola - Resources for Health Professionals". www.cdc.gov. Retrieved 2019-11-14.
- ^ a b c "WHO | Fascioliasis diagnosis, treatment and control strategy". WHO. Retrieved 2019-11-18.
- ^ a b c "Medical Chemical Corporation: Para-site". www.med-chem.com. Retrieved 2019-11-14.
- ^ Dalton, J. P. (John Pius), 1958- (1999). Fasciolosis. CABI Pub. ISBN 0851992609. OCLC 39728053.
{{cite book}}: CS1 maint: multiple names: authors list (link) CS1 maint: numeric names: authors list (link) - ^ Caron, Yannick; Celi-Erazo, Maritza; Hurtrez-Boussès, Sylvie; Lounnas, Mannon; Pointier, Jean-Pierre; Saegerman, Claude; Losson, Bertrand; Benítez-Ortíz, Washington (2017). "IsGalba schirazensis(Mollusca, Gastropoda) an intermediate host ofFasciola hepatica(Trematoda, Digenea) in Ecuador?". Parasite. 24: 24. doi:10.1051/parasite/2017026. ISSN 1776-1042.
- ^ Pottinger, Paul S.; Jong, Elaine C. (2017), "Trematodes", The Travel and Tropical Medicine Manual, Elsevier, pp. 588–597, ISBN 9780323375061, retrieved 2019-11-14
- ^ Mòdol, Xavier (2018-10-26), "The challenge of providing primary health care services in crisis countries in the Eastern Mediterranean Region", Family Practice In The Eastern Mediterranean Region, CRC Press, pp. 137–152, ISBN 9781351016032, retrieved 2019-11-18
- ^ a b "Fasciola". web.stanford.edu. Retrieved 2019-11-18.
- ^ "History". web.stanford.edu. Retrieved 2019-11-14.
- ^ "Watercress and Parasitic Infection". www.cfs.gov.hk. Retrieved 2019-11-14.
- ^ "Prevention". web.stanford.edu. Retrieved 2019-11-18.
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