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Advertisements Table of Contents Fasciola hepatica – ClassificationKingdomAnimaliaPhylumPlatyhelminthesClassTrematodaSubclassDigeneaOrderEchinostomidaGenusFasciolaSpecieshepaticaFasciola hepaticaFasciola hepatica, also referred to as the common liver fluke or sheep liver fluke, is a parasitic trematode of the class Trematoda, phylum Platyhelminthes. It infects the livers of numerous mammals, including humans, and is transmitted worldwide by sheep and cattle.This neglected tropical disease is known as fasciolosis or fascioliasis. It is a form of helminthiasis.Currently, fasciolosis is classified as a plant/food-borne trematode infection, typically acquired by ingesting the parasite’s plant-encrusted metacercariae.F. hepatica, which is found worldwide, has been recognized for decades as a significant parasite of sheep and cattle, causing up to £23 million in economic losses in the United Kingdom alone.Due to its comparatively large size and economic significance, it has been the subject of numerous scientific studies and may be the most well-known species of trematode.Fasciola gigantica is the closest relative of F. hepatica. These two flukes are sister species; they share numerous morphological characteristics and can mate.General CharacteristicsAs an endoparasite, Fasciola hepatica is located in the bile duct of the liver of sheep.The body is dorso-ventrally compressed and resembles a leaf, measuring approximately 25-30 mm in length and 4-5 mm in width.The anterior extremity forms a conical protrusion known as the cephalic cone.The mouth is located anteriorly and ventrally, and it is encompassed by oral sucker.A muscular ventral sucker or acetabulum is located slightly behind the oral sucker.The posterior end is large and frontally more convex than it is posteriorly.The digestive system includes the esophagus, the pharynx, and the diverticulated intestine.The location of the excretory pore is at the posterior extremity.They are hermaphrodites, possessing both male and female reproductive organs.Between the ventral and oral suckers, there exists a median genital pore through which the ova exit.Habitat of Fasciola hepaticaFasciola hepatica, also known as the common liver fluke, has a complex lifecycle that involves several different hosts and habitats. As an adult parasite, it primarily resides in the bile ducts of the liver of its definitive host, which can include a range of mammals, including humans, sheep, cattle, and other domesticated animals. The adult fluke feeds on blood and tissue fluids and reproduces by releasing eggs that pass out of the host through the feces.Once outside the host, the eggs hatch into larvae that infect a suitable intermediate host, typically a snail, where they develop into free-swimming cercariae that are released into the water. These cercariae then infect the definitive host through ingestion of contaminated water or vegetation.In addition to its hosts, F. hepatica can also be found in various environmental habitats, such as wetlands, marshes, and other areas with standing or slow-moving water, which are suitable for the snail intermediate hosts. The parasite has a wide distribution and can be found in temperate regions throughout the world, although it is most prevalent in areas with wet, marshy conditions.Hosts of Fasciola hepaticaFasciola hepatica and F. gigantica are parasites of domestic and untamed ruminants (typically sheep, cattle, and goats; also camelids, cervids, and buffalo). Infections occasionally occur in equids, lagomorphs, macropods, and rodents, which are aberrant, non-ruminant herbivore hosts. Detection of Fasciola spp. ova in the feces of carnivores is likely an artifact of consumption of contaminated liver.The intermediary snail hosts for Fasciola species are members of the family Lymnaeidae, specifically Lymnaea, Galba, Fossaria, and Pseudosuccinea. At least 20 species of snail have been identified as intermediate hosts for one or more species of Fasciola. The suitability of snail species to function as intermediate hosts for F. hepatica versus F. gigantica may vary; research into the host ranges of both Fasciola spp. is ongoing.History and distribution of Fasciola hepaticaFasciola hepatica, also known as the common liver fluke, is a parasitic flatworm that infects a range of mammals, including humans, as well as some birds. It is primarily found in temperate regions worldwide, with the highest prevalence in areas with wet, marshy conditions.The history of F. hepatica dates back to ancient times, with evidence of its presence found in the remains of human and animal mummies from ancient Egypt. The parasite has also been identified in the remains of prehistoric animals, such as the woolly mammoth. F. hepatica has been recognized as a veterinary and human pathogen since the early 19th century, with the first recorded case of human infection reported in the 1860s in Europe.Today, F. hepatica is found throughout much of the world, particularly in regions with high levels of livestock production. It is prevalent in Europe, Asia, Africa, and the Americas, and is responsible for significant economic losses in the agricultural sector due to decreased productivity and the cost of treating infected livestock. In humans, F. hepatica infection is most common in developing countries, particularly in areas where people consume raw or undercooked freshwater plants, such as watercress, that have been contaminated with the parasite.Epidemiology of Fasciola hepaticaWhen cyst-covered aquatic vegetation is consumed or when water containing metacercariae is consumed, infection begins. F. hepatica causes disease in ruminants frequently in the United Kingdom between March and December.By consuming watercress or the Peruvian beverage ‘Emoliente’, which contains drops of watercress liquid, humans become infected. When cattle and sheep consume the infectious stage of the parasite from low-lying, damp pasture, they become infected.Infections in humans have been reported from more than 75 countries worldwide. In Asia and Africa, both F. hepatica and F. gigantica cause human fasciolosis, whereas in South and Central America and Europe, only F. hepatica is responsible.Bovine tuberculosis detection can be hindered by the presence of F. hepatica. Cattle co-infected with F. hepatica have a weaker reaction to the single intradermal comparative cervical tuberculin (SICCT) test than those infected with M. bovis alone. Consequently, an infection with F. hepatica can make it difficult to detect bovine tuberculosis; this is, of course, a significant issue in the agricultural sector.Morphology of Fasciola hepatica/Structure of Fasciola HepaticaShape, Size and ColourThe body of F. hepatica is slender, leaf-shaped, dorsoventrally flattened, elongated, and oval. It is approximately 25 to 30 mm long and 4 to 12 mm wide.The maximum width occurs in the anterior third of the body, where the body tapers anteriorly and posteriorly; however, the anterior end is somewhat convex, whereas the posterior end is sharply pointed. The greatest breadth of F. indica occurs roughly in the middle of the body, and the tail is rounded. It is typically pinkish in color, but appears brownish due to the host’s bile.External MorphologyF. hepatica is an animal with a delicate, leaf-like body and bilateral symmetry. They range in length from 1 to 2.5 centimeters and width from 1 centimeter.The anterior end of the body is extended into a prominent conical projection known as the oral cone or head lobe, which bears at its apex a triangular opening, the mouth, and is surrounded by the oral or anterior sucker.On the ventral surface, slightly posterior to the head lobe, is a much larger sucker known as the ventral or posterior sucker (also known as the acetabulum). The genital orifice, through which the penis occasionally protrudes, is located between the two suckers and near the posterior sucker. The excretory aperture, which is a singular opening, is located at the body’s extreme posterior tip.The Laurel canal opens in the center of the dorsal surface. Spinules or papillae, which are extensions of the cuticle that surrounds the body, protrude from the body’s surface.Internal MorphologyThe architecture of F. hepatica’s body wall is unique and consists of the following sequence of layers: the external layer of the skin, the epidermis (formerly known as the cuticle), from which spinules originate;A subterranean membrane;Circular, longitudinal and oblique or diagonal muscle fibres; andA collection of unicellular gland cells that contain protoplasmic processes. Interorgan spaces are densely populated with parenchyma cells. Numerous ectodermal dells are sunk into the parenchyma and linked to the cuticle by protoplasmic projections.Body Wall of Fasciola HepaticaIn contrast to turbellarians, the body wall of F. hepatica is devoid of an epidermal cellular layer. However, it is composed of a dense layer of cuticle, a thin basement membrane, and layers of muscle beneath the mesenchyme. Advertisements![]() The respiration process is anaerobic or anoxybiotic. In reality, glycogen is metabolized into carbon dioxide and fatty acids, releasing heat-based energy. The procedure consists of the subsequent steps: AdvertisementsGlycogen undergoes anaerobic glycolysis in order to produce pyruvic acid.Pyruvic acid is decarboxylated in order to produce carbon dioxide and an acetyl group.The acetyl group then combines with coenzyme A to form acetyl coenzyme A, and (iv) acetyl coenzyme A is then transported to the mitochondria.The acetyl coenzyme A is then reduced and condensed to produce fatty acids.Thus, carbon dioxide is diffused out through the body’s general surface, and fatty acids are excreted via the excretory system.Excretory System of Fasciola HepaticaBoth excretion and osmoregulation are priorities for Fasciola hepatica’s excretory system. It is made up of several flame cells, flame bulbs, or protonephridia that are connected by a network of excretory channels. ![]() ![]() ![]() Fasciola hepatica is hermaphrodite, but cross-fertilization typically occurs. The reproductive organs are complex and well-developed. Advertisements1. Male Reproductive System of Fasciola HepaticaTestes, vasa deferens, seminal vesicle, ejaculatory duct, cirrus or penis, prostate glands, and genital atrium make up the male reproductive system. a. TestesThese are two in number, highly ramified tubular structures located one behind the other (i.e., in tandem) in the body’s posterior middle region. In fact, they occupy a considerable amount of space behind the middle portion of Fasciola’s body. The cells that line the testicular wall give birth to spermatozoa.b. Vasa DeferentiaEach testis produces a vas deferens or sperm duct that travels forward and is slender and narrow.c. Seminal VesicleThe two vasa deferentia unite near the acetabulum (ventral sucker) and enlarge to form the vesicula seminalis, a muscular, elongated, broad, bag-like seminal vesicle. It provides the function of sperm storage.d. Ejaculatory DuctThe seminal vesicle continues anteriorly into the ejaculatory duct, a very narrow and convoluted duct.e. CirrusThe ejaculatory duct emerges into the muscular and elongated cirrus of the penis. The cirrus opens through the male genital orifice in a shared genital atrium. F. indica’s cirrus is coated in small spines.f. Prostate GlandsA large number of unicellular prostate glands encircle the ejaculatory duct. The alkaline secretion of these glands, which opens into the ejaculatory duct, facilitates the free migration of sperm during copulation.g. Genital AtriumThe genital atrium is a chamber shared by male and female genital openings; it is externally accessible via a gonopore located ventrally in front of the acetabulum. During copulation, the cirrus can be expelled through the gonopore. The penis, seminal vesicle, and prostatic organs are encased in a cirrus sheath or sac.![]() The female reproductive system consists of the ovary, the oviduct, the uterus, the vitelline glands, Mehlis’ glands, and Laurer’s canal. AdvertisementsOvary: The singular, tubular, and highly branched ovary is located anterior to the testes on the right side of the anterior one-third of the body.Oviduct: All ovarian branches terminate in a short, slender conduit known as the oviduct. The oviduct descends perpendicularly and connects to the median vitelline duct.Uterus: From the confluence of the oviduct and median vitelline duct arises a large, convoluted uterus containing fertilized eggs or capsules. The uterus opens into the common genital atrium on the left side of the male genital aperture via the female genital aperture. The uterus is relatively small and located in front of the testes and ovaries. The terminal portion of the uterus, known as the metraterm, has muscular walls that eject the ova and sometimes receive the cirrus during copulation.![]() ![]() F. hepatica undergoes indirect development, involving four varieties of free-swimming and parasitic larval stages. Fasciola is digenetic, and its life cycle consists of at least two infective stages at all times. Two or more hosts are infected prior to the completion of its life cycle. The definitive or primary host is a vertebrate (sheep), whereas the intermediate host is a gastropod (Lymnaea, Planorbis, etc.). ![]() As an endoparasite that resides in the liver and bile ducts of sheep, Fasciola hepatica is well adapted to its parasitic lifestyle. In fact, the adult fluke displays a number of adaptive characteristics, and its various life stages also account for a number of adaptive characteristics. AdvertisementsTherefore, Fasciola hepatica’s adaptive characteristics can be discussed under the following two headings: 1. Adaptations of the Adult FlukeIts dorsoventrally compressed, leaf-shaped body increases the body’s surface area for increased diffusion of substances through the body’s fluid.Its body is clothed with a thick cuticle that protects it from the antitoxins of its host.Cilia are absent in adult flukes.Well-developed adhesive organs such as suckers (anterior sucker and ventral sucker) that provide a firm attachment to the recipient tissue. Numerous cuticular spines on its body erode the host tissue that serves as its sustenance and also prevent the fluke from being expelled from the bile ducts.It has an anteriorly located mouth and a muscular pharynx for drawing nutrients from the host body. Since it nourishes on pre-digested and digested substances from the host, its alimentary canal and digestive glands are not well developed.Since there is no digestion, there is no anus; consequently, there is no circulatory system, as the various organs of the alimentary canal (intestine and its various branches) do not distribute the already digested food substances to the various portions of the body.Because it resides in an oxygen-depleted environment, anaerobic respiration occurs; respiratory organs are wholly absent.As flukes are endoparasites, its nervous system is very rudimentary and its sense organs are completely absent.There are no locomotory organs in flukes because they live in a protected environment.The excretory system is comprised of a complex network of branched tubules to facilitate the collection of the body’s various metabolic byproducts.The reproductive system is highly developed and optimally tailored to the parasitic lifestyle of the organism.Since the adult fluke resides in the body of the sheep, it may perish along with the animal. Therefore, a secondary host is required for the transmission of the parasite from one host to another, so that the parasite’s race can continue. The snail is therefore the secondary host.2. Adaptations in Life HistoryFasciola hepatica’s numerous parasitic adaptation traits can be traced back to the following stages of the parasite’s life cycle: AdvertisementsOne solution to the problem of eggs being wasted during transfer is to produce an extremely high volume of eggs.The fertilized eggs are protected from the enzymes of the host by a chitinous covering, the shell, which allows them to travel down the bile duct into the gut of the sheep and subsequently out with its feces. Eggs with a protective shell are known as capsules.The first larvae to emerge from the capsules are called miracidia, and they are perfectly suited to a life of free swimming (thanks to their ciliated bodies and the development of eye spots) and to entering the body of the secondary host, Limnaea, Planorbis, etc. (thanks to their penetration glands).The sporocyst is a parasite whose body is wrapped in a cyst-like structure to avoid being digested by the snail’s digestive enzymes. The sporocyst’s germ balls develop into rediae, which can then give rise to either more rediae or cercariae.Five, rediae (lappets or procruscula) and cercariae (tail) may travel and find their way into the fresh tissues of the snail thanks to their locomotory organs.Six, after escaping the snail’s body, the cercariae have a brief period of freedom before returning to a cyst they’ve secreted on plants.Due to their herbivorous diet, sheep are a perfect host for cysted cercariae termed metacercariae that live on plant matter.The cyst provides the metacercariae with protection from the elements, allowing them to wait for admission into the sheep’s body for an extended period of time.The larvae’s parthenogenetic mode of reproduction also guarantees the survival of their species.The rapid reproductive rate, specialized larvae, sexual and asexual reproduction, and morphological and physiological adaptations of the fluke all serve a single purpose: to guarantee the species’ continued existence.Life Cycle of Fasciola Hepatica Summery![]() Fasciola hepatica, also known as the common liver fluke, is a parasitic flatworm that infects a range of mammals, including humans, as well as some birds. How is F. hepatica transmitted?F. hepatica is transmitted through the consumption of contaminated water or vegetation, particularly freshwater plants such as watercress, that have been contaminated with the parasite. What are the symptoms of F. hepatica infection in humans?Symptoms of F. hepatica infection in humans can include abdominal pain, diarrhea, fever, and fatigue. In severe cases, the infection can lead to liver damage, jaundice, and other serious complications. How is F. hepatica diagnosed in humans?F. hepatica infection is typically diagnosed through a combination of clinical evaluation, laboratory testing, and imaging studies, such as ultrasound or CT scans, to detect evidence of liver damage or the presence of the parasite. What is the treatment for F. hepatica infection?The primary treatment for F. hepatica infection in humans is a course of antiparasitic medications, such as triclabendazole, which is effective against the adult parasite in the liver. Can F. hepatica infection be prevented?F. hepatica infection can be prevented through a range of measures, including avoiding consumption of contaminated water or vegetation, thoroughly cooking meat, and practicing good hygiene and sanitation. What is the economic impact of F. hepatica in livestock?F. hepatica infection can have a significant economic impact on the agricultural sector, particularly in areas with high levels of livestock production, due to decreased productivity and the cost of treating infected animals. What is the lifecycle of F. hepatica?The lifecycle of F. hepatica involves several different hosts and habitats, with the adult parasite residing in the bile ducts of the liver of its definitive host, while the intermediate hosts are typically snails. Is F. hepatica infection common in humans?F. hepatica infection is relatively uncommon in humans, particularly in developed countries, although it remains a significant public health concern in many developing countries. Can F. hepatica infection be fatal?In rare cases, F. hepatica infection can lead to serious complications, including liver damage and other life-threatening conditions, particularly in individuals with weakened immune systems or underlying medical conditions. Referenceshttps://www.cdc.gov/dpdx/fascioliasis/index.htmlhttps://byjus.com/biology/fasciola-hepatica-diagram/https://en.wikipedia.org/wiki/Fasciola_hepaticahttps://www.biologydiscussion.com/invertebrate-zoology/phylum-platyhelminthes/fasciola-hepatica-habitat-structure-and-life-history/28888https://www.notesonzoology.com/animals/study-notes-on-fasciola-hepatica-platyhelminthes/1735https://www.notesonzoology.com/zoology/distinguish-between-taenia-solium-and-fasciola-hepatica/3116 |
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