Fasciola hepatica- Common liver fluke or Sheep liver fluke
Fasciola hepatica is a parasitic flatworm that belongs to the class Trematoda and the phylum Platyhelminthes. It is also known as the common liver fluke or the sheep liver fluke, because it mainly infects the livers of sheep and cattle, as well as other herbivorous mammals . Humans can also become infected by ingesting contaminated water plants or water containing the larval stage of the parasite .
Fasciola hepatica has a worldwide distribution, especially in temperate regions where sheep and cattle are raised. It is estimated that up to 17 million people are infected and that another 180 million are at risk of infection . Fascioliasis, the disease caused by F. hepatica, can cause significant economic losses in livestock production and serious health problems in humans .
Fasciola hepatica has a complex life cycle that involves two hosts: a definitive host (usually a herbivore) and an intermediate host (a freshwater snail of the family Lymnaeidae). The adult worms live in the bile ducts of the definitive host and produce eggs that are passed in the feces. The eggs hatch in freshwater and release miracidia, which infect the snails. Inside the snails, the miracidia develop into sporocysts, rediae, and cercariae. The cercariae emerge from the snails and encyst on aquatic plants or water as metacercariae. The metacercariae are the infective stage for the definitive host, which acquires them by eating the plants or drinking the water. The metacercariae excyst in the intestine of the definitive host and migrate through the abdominal cavity and the liver tissue to reach the bile ducts, where they mature into adult worms .
Fasciola hepatica can cause different clinical manifestations depending on the stage of infection and the number of parasites. The acute phase occurs during the migration of the larvae through the liver and is characterized by fever, abdominal pain, hepatomegaly, eosinophilia, and sometimes vomiting, diarrhea, urticaria, anemia, or jaundice. The chronic phase occurs when the adult worms settle in the bile ducts and is characterized by biliary obstruction, inflammation, fibrosis, cirrhosis, cholangitis, cholecystitis, or cholangiocarcinoma. Ectopic infections can also occur when the larvae migrate to other organs such as the lungs, brain, eyes, or skin .
The diagnosis of fascioliasis is based on the detection of eggs in stool or bile samples, serological tests for antibodies or antigens, molecular methods for parasite DNA, or imaging techniques for liver lesions. The treatment of choice is triclabendazole, which is effective against both immature and mature worms. Other drugs such as bithionol or nitazoxanide can be used as alternatives. The prevention of fascioliasis relies on health education, sanitation, control of snail populations, disinfection of water plants or water sources, and treatment of infected animals or humans .
Fasciola hepatica is one of the oldest known parasites of humans and animals. It was first discovered more than 600 years ago by Jehan de Brie, who observed the cercariae of F. hepatica in a snail and the adult flukes infecting sheep. It was later named by Linnaeus in 1758.
F. hepatica is the largest and most common liver fluke that infects humans, but its primary hosts are sheep and cattle. It causes a disease called fascioliasis or liver rot, which can have serious economic and health impacts on livestock production and human health.
F. hepatica has a worldwide distribution, especially in temperate regions where sheep and cattle are raised and where people consume raw or undercooked aquatic plants contaminated with the infective larvae of the parasite. It has been estimated that up to 17 million people are infected and that another 180 million are at risk of infection.
F. hepatica can also infect other vertebrates such as goats, deer, horses, dogs, pigs, and occasionally humans. Its intermediate hosts are freshwater snails of the family Lymnaeidae, such as Planorbis, Bulinus, or Limnaea species. The parasite has a complex life cycle that involves two different kinds of hosts: a definitive host (a vertebrate) where the adult worms live and reproduce in the bile ducts of the liver, and an intermediate host (a snail) where the larval stages develop and multiply.
Fasciola hepatica is an endoparasite that lives in the liver and bile duct of its definitive host, which can include various mammals such as humans, sheep, cattle, and other domesticated animals . It is also known as the common liver fluke or the sheep liver fluke because it causes a disease called fascioliasis or liver rot in sheep and cattle .
The adult worm of Fasciola hepatica has a flat, leaf-shaped, elongated and oval body that measures about 25 to 30 mm in length and 4 to 12 mm in breadth . It has two muscular suckers: an oral sucker at the tip of its anterior conical projection that surrounds the mouth, and a ventral sucker at the base of the cone that helps it to attach to the lining of the biliary ducts . The adult worm lives in the biliary tract of the definitive host for many years and produces eggs that are passed out with the feces .
The habitat of Fasciola hepatica is influenced by its complex life cycle that involves two hosts: a primary vertebrate host and a secondary or intermediate invertebrate host, which is usually a freshwater snail of the family Lymnaeidae . The eggs of Fasciola hepatica hatch in freshwater and release miracidia, which are free-swimming larvae that infect the snail host. Inside the snail, the miracidia undergo several developmental stages and produce cercariae, which are another type of larvae that escape from the snail and encyst on aquatic plants such as watercress. These encysted larvae are called metacercariae and they are the infective stage for the definitive host. When an animal or a human ingests water plants contaminated with metacercariae, the larvae excyst in the duodenum and penetrate into the peritoneum and then into the liver capsule. From there, they migrate through the liver parenchyma until they reach the bile ducts, where they mature into adult worms .
The habitat of Fasciola hepatica is therefore determined by its adaptation to different environments and hosts. It can survive in various climatic conditions and geographical regions where sheep or cattle are raised and where people consume raw aquatic vegetables contaminated with metacercariae . It can also cause infection in other animals such as deer, horse, dog, ass, ox and occasionally man . Fasciola hepatica is found on all inhabited continents except Antarctica, in more than 70 countries. It has been estimated that up to 17 million people are infected and that another 180 million are at risk.
Fasciola hepatica is a flat, leaf-shaped fluke that belongs to the class Trematoda. It has two distinct morphological stages: the adult worm and the egg.
Adult worm of Fasciola hepatica
The adult worm of F. hepatica is large enough to be seen by the naked eye, measuring about 3 cm in length and 1.5 cm in width . It has a gray or brown color and a smooth surface. It has a conical projection at the anterior end, which contains an oral sucker that surrounds the mouth. Below the oral sucker, there is a ventral sucker that helps the worm to attach to the lining of the bile ducts of the definitive host. The worm has a bifurcated and incomplete intestine that branches laterally. The worm also has a complex reproductive system that includes both male and female organs, making it hermaphroditic. The adult worm can live for several years in the biliary tract of the host and produce eggs continuously.
|Size||3 cm x 1.5 cm|
|Color||Gray or brown|
|Shape||Flat and leaf-like|
|Anterior end||Conical projection with oral sucker|
|Ventral sucker||Below oral sucker|
|Intestine||Bifurcated and incomplete|
Eggs of Fasciola hepatica
The eggs of F. hepatica are yellow-brown, large, ovoid, operculated, and bile-stained . They measure about 140 μm by 80 μm and have a smooth shell with a double line . The eggs contain an immature larva called a miracidium . The eggs are unembryonated when freshly passed in the feces of the host . They require freshwater and oxygen to develop into embryonated eggs that can release miracidia . The eggs of F. hepatica are indistinguishable from those of Fasciolopsis buski, another fluke that infects humans .
|Size||140 μm x 80 μm|
|Shape||Ovoid and operculated|
|Surface||Smooth with double line|
|Contents||Unembryonated or embryonated miracidium|
Fasciola hepatica is a parasitic flatworm that causes a disease called fascioliasis in humans and animals. It has a complex life cycle that involves two hosts: a definitive host (usually a sheep, cattle or human) and an intermediate host (a freshwater snail of the family Lymnaeidae).
The life cycle of F. hepatica can be summarized as follows :
- Immature eggs are discharged in the bile ducts of the definitive host and passed in the feces.
- Eggs become embryonated in freshwater over about two weeks; embryonated eggs release miracidia, which are ciliated larvae that swim and seek a suitable snail host.
- In the snail, the miracidia penetrate the soft tissues and undergo several developmental stages: sporocysts, rediae and cercariae. These stages multiply asexually and produce thousands of cercariae per snail.
- The cercariae are released from the snail and swim in the water until they find aquatic vegetation or other substrates where they encyst as metacercariae. These are the infective stage for the definitive host.
- Humans and other mammals become infected by ingesting metacercariae-contaminated vegetation (e.g., watercress) or water.
- After ingestion, the metacercariae excyst in the duodenum and penetrate through the intestinal wall into the peritoneal cavity. The immature flukes then migrate through the liver parenchyma into the bile ducts, where they mature into adult flukes and produce eggs. This process takes about three to four months.
The following table shows the approximate duration and location of each stage of the life cycle:
|Miracidium||A few hours||Freshwater|
|Sporocyst||2 weeks||Snail tissues|
|Redia||4 weeks||Snail tissues|
|Cercaria||A few hours||Freshwater|
|Immature fluke||3-4 months||Definitive host`s intestine, peritoneum and liver|
|Adult fluke||Several years||Definitive host`s bile ducts|
The life cycle of F. hepatica is illustrated in the following image:
The main mode of transmission of Fasciola hepatica infection to humans and other definitive hosts is through the ingestion of raw or undercooked water plants, such as watercress, that are contaminated with metacercariae. Metacercariae are the infective stage of the parasite that encyst on aquatic vegetation after leaving the snail intermediate host. The snails, belonging to the family Lymnaeidae, are infected by the miracidia that hatch from the eggs passed in the feces of the definitive host.
Other possible modes of transmission include drinking water contaminated with metacercariae, eating raw liver from infected animals, or using traditional medicines that contain water plants. However, these modes are less common and less efficient than ingesting water plants.
The risk of transmission is higher in areas where sheep and cattle are raised and where people consume raw aquatic vegetables. The prevalence of infection is also influenced by environmental factors such as temperature, rainfall, irrigation, and snail population dynamics.
Fascioliasis is a parasitic infection caused by the liver flukes Fasciola hepatica and Fasciola gigantica, which are acquired by eating contaminated water plants such as watercress. The clinical manifestations of fascioliasis vary depending on the stage of infection, the number and location of the parasites, and the host immune response. The clinical course of fascioliasis can be divided into four phases:
- Incubation period: This is the period from ingestion of metacercariae (the infective larvae) to appearance of the first symptom. This period can range from a few days to a few months, depending on the parasite load and host factors.
- Acute phase: This is the period of migration of the larvae from the duodenum to the liver and bile ducts. This period ranges from 2 to 4 months after infection. The acute phase is characterized by local or systemic allergic and toxic reactions due to tissue damage and inflammation caused by the migrating larvae. The most common symptoms are fever, right upper quadrant pain, hepatomegaly (enlarged liver), and eosinophilia (increased number of eosinophils in the blood). Other symptoms may include vomiting, diarrhea, urticaria (hives), anemia, cough, shortness of breath, chest pain, and lymphadenopathy (swollen lymph nodes). The acute phase is rarely seen in humans and occurs when a large number of metacercariae are ingested at once .
- Latent phase: This is an asymptomatic phase that involves the period of maturation of the parasites and beginning of egg production. This period can range from months to years after infection. It is marked by persistent eosinophilia and occasionally relapses of gastrointestinal symptoms of the acute phase. The latent phase may be interrupted by complications such as cholangitis (inflammation of the bile ducts), cholecystitis (inflammation of the gallbladder), pancreatitis (inflammation of the pancreas), or liver abscesses.
- Chronic phase: This is the phase marked by chronic inflammation, hyperplasia, and fibrosis of the bile ducts and gallbladder due to the presence of adult worms and eggs. The symptoms of this phase are mainly related to biliary obstruction and dysfunction, such as biliary colic (severe pain in the upper abdomen), nausea, intolerance to fatty food, right upper quadrant pain, epigastric pain, obstructive jaundice (yellowing of the skin and eyes due to bile accumulation), and pruritus (itching). Biliary lithiasis (gallstones) is another manifestation of the chronic phase. The chronic phase can last for several years and may lead to complications such as portal hypertension (high blood pressure in the portal vein), portal cirrhosis (scarring of the liver due to portal hypertension), bleeding esophageal varices (enlarged veins in the esophagus that can rupture and bleed), ascites (fluid accumulation in the abdomen), hepatic encephalopathy (brain dysfunction due to liver failure), or death .
In addition to these phases, fascioliasis can also present as ectopic or aberrant infections, where the larvae migrate to sites other than the liver or bile ducts. These sites may include the gastrointestinal tract, abdominal wall subcutaneous tissue, pancreas, spleen, heart, lungs, brain, eyes, or skin. Ectopic fascioliasis can cause various symptoms depending on the organ involved, such as abdominal pain, dysphagia (difficulty swallowing), foreign body sensation in the throat, airway obstruction, hemoptysis (coughing up blood), pleural effusion (fluid accumulation in the chest cavity), pericarditis (inflammation of the sac around the heart), myocarditis (inflammation of the heart muscle), meningitis (inflammation of the membranes around the brain and spinal cord), seizures, visual impairment, or subcutaneous nodules .
Fascioliasis is a parasitic infection caused by the liver flukes Fasciola hepatica and Fasciola gigantica. The diagnosis of fascioliasis can be challenging because the clinical manifestations are nonspecific and the eggs are not detectable in the stool until 2 to 4 months after infection. Therefore, a combination of different diagnostic methods may be required to confirm the infection. Some of the commonly used diagnostic methods are:
- Stool microscopy: This is the most definitive method of diagnosis, as it can demonstrate the presence of typical operculated eggs in the feces or duodenal aspirates of infected patients. However, stool microscopy has some limitations, such as low sensitivity in acute cases, inability to differentiate between F. hepatica and F. gigantica or other similar eggs, and dependence on the quality of the specimen and the expertise of the microscopist .
- Blood picture: This can reveal eosinophilia, which is a common feature of fascioliasis, especially in the acute phase. However, eosinophilia is not specific for fascioliasis and can be seen in other helminthic infections or allergic conditions.
- Serological test: This can detect specific antibodies against Fasciola antigens in the serum of infected patients. Serological tests are useful for screening and diagnosis of acute and chronic cases, as well as for epidemiological studies and monitoring of treatment response. The most widely used serological test is the enzyme-linked immunosorbent assay (ELISA), which has a high sensitivity (95%) and specificity (98%). Other serological tests include counterimmunoelectrophoresis, indirect hemagglutination, immunoblotting, and immunofluorescence .
- Molecular methods: These can identify Fasciola DNA in stool, serum, or tissue samples using polymerase chain reaction (PCR) or hybridization techniques. Molecular methods are useful for species identification, genotyping, and detection of mixed infections . However, they are not widely available and require specialized equipment and expertise.
- Imaging: This can reveal the characteristic lesions of fascioliasis in the liver and biliary tract using ultrasonography, computed tomography (CT), magnetic resonance imaging (MRI), or endoscopic retrograde cholangiopancreatography (ERCP). Imaging can also help to exclude other causes of liver disease, such as abscesses, tumors, or stones .
- Others: These include detection of Fasciola coproantigens in stool samples using ELISA or immunochromatographic tests, which are useful for chronic cases and evaluation of treatment efficacy . Another method is measurement of serum IgE and IgG4 antibodies, which are elevated in fascioliasis and may correlate with disease severity and activity.
Fascioliasis is a parasitic infection caused by two species of liver flukes, Fasciola hepatica and Fasciola gigantica. The infection can affect the liver, bile ducts, and other organs of humans and animals. The symptoms of fascioliasis can vary depending on the stage and severity of the infection, but they may include fever, abdominal pain, jaundice, anemia, and eosinophilia.
The treatment options for fascioliasis are limited, as most common anthelmintics have poor efficacy against the flukes. The only effective therapy for human fascioliasis is triclabendazole, a benzimidazole derivative that was first used in animals in the 1980s and in humans in 1986. Triclabendazole was approved by the US Food and Drug Administration (FDA) in 2019 for the treatment of human fascioliasis in patients aged 6 years and older. It is also available through a donation program by the manufacturer and administered by the World Health Organization (WHO) in endemic countries.
Triclabendazole works by inhibiting the tubulin polymerization and microtubule formation in the flukes, leading to their paralysis and death. Triclabendazole has high efficacy against both immature and mature forms of the flukes, and can be used in both acute and chronic phases of the infection. The recommended dose of triclabendazole is 10 mg/kg as a single oral dose with food . The drug is well tolerated, with mild and transient adverse effects such as nausea, vomiting, abdominal pain, headache, dizziness, and pruritus .
The alternative drug for fascioliasis is bithionol, a halogenated phenol that was used before triclabendazole became available. Bithionol has a lower efficacy than triclabendazole and requires a longer course of treatment (30-50 mg/kg for 10-15 days). Bithionol can also cause serious side effects such as photosensitivity, skin rash, diarrhea, and hepatotoxicity. Bithionol is no longer used or available in many countries due to safety issues and unavailability.
Other drugs that have been tried for fascioliasis include emetine, dehydroemetine, praziquantel, albendazole, mebendazole, oxyclozanide, nitazoxanide, and artemisinin derivatives. However, none of these drugs have shown consistent or satisfactory efficacy against the flukes . Some of these drugs may also have serious adverse effects or contraindications. Therefore, they are not recommended for the treatment of fascioliasis.
In some cases, surgical or endoscopic interventions may be required to remove the flukes or relieve the biliary obstruction caused by them. However, these procedures are not curative and may be associated with complications. Therefore, they should be reserved for patients who do not respond to medical treatment or have severe symptoms.
In summary, triclabendazole is the drug of choice for the treatment of human fascioliasis. It has high efficacy, good safety profile, and simple dosing regimen. Bithionol is an alternative drug but has lower efficacy and more side effects. Other drugs are not effective or safe for fascioliasis. Surgical or endoscopic procedures may be needed in some cases but are not curative.
Fascioliasis is a parasitic disease caused by liver flukes of the genus Fasciola, which can infect humans and animals. The main mode of transmission is through ingestion of water plants or water contaminated with metacercariae, the infective larval stage of the parasite. Fascioliasis can cause acute and chronic symptoms, such as fever, abdominal pain, hepatomegaly, eosinophilia, biliary obstruction, and cirrhosis. Therefore, it is important to prevent and control this disease in endemic areas.
Fascioliasis can be prevented by following these measures:
- Health education: People should be aware of the risk factors and symptoms of fascioliasis, and seek medical attention if they suspect infection. They should also be informed about the life cycle of the parasite and how to avoid exposure to contaminated water plants or water. Health education campaigns can be conducted through mass media, community meetings, school programs, and health workers.
- Improving sanitation: The disposal of human and animal feces should be done in a hygienic manner, to prevent contamination of water sources and irrigation systems. Proper sewage treatment and disposal facilities should be available and maintained. Sanitary latrines should be used and cleaned regularly.
- Preventing pollution of watercourses: The use of chemical fertilizers and pesticides should be minimized or avoided in areas where water plants are grown or consumed. Organic farming methods should be encouraged and promoted. Water quality monitoring and testing should be conducted regularly to detect any contamination by Fasciola eggs or larvae.
- Proper disinfection of watercress and other water vegetations: Water plants that are eaten raw or cooked should be thoroughly washed and disinfected before consumption. This can be done by soaking them in boiling water for at least 10 minutes, or in a solution of vinegar or salt for at least 30 minutes. Alternatively, they can be peeled or discarded if they have any signs of damage or infection.
- Control of snails: Snails are the intermediate hosts of Fasciola parasites, and they play a crucial role in the transmission cycle. Snail control methods include environmental modification, biological control, chemical control, and mechanical control. Environmental modification involves draining or filling stagnant water bodies, removing aquatic vegetation, improving water flow and drainage, and reducing organic matter that serves as food for snails. Biological control involves introducing natural predators or parasites of snails, such as fish, ducks, crayfish, or trematode larvae. Chemical control involves applying molluscicides (snail-killing agents) to water bodies where snails are abundant. Mechanical control involves manual removal or destruction of snails by hand-picking, trapping, crushing, or burning.
- Treatment of infected persons: Infected persons should be diagnosed and treated promptly with effective anthelmintic drugs, such as triclabendazole or bithionol. Treatment can reduce the worm burden and egg production, thus preventing further transmission and complications. Treatment can also reduce the morbidity and mortality associated with fascioliasis.
By implementing these preventive measures, fascioliasis can be reduced or eliminated in endemic areas. This can improve the health and well-being of humans and animals, as well as the economic and social development of the affected communities.
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