Trematodiasis is a group of parasitic infections due different species of flukes, the trematodes.[4] Symptoms can range from mild to severe depending on the species, number and location of trematodes in the infected organism.[1] Symptoms depend on type of trematode present, and include chest and abdominal pain, high temperature, digestion issues, cough and shortness of breath, diarrhoea and change in appetite.[1][2]
Trematodiases can be transmitted through food or water that contains larval forms of the parasite.[5][1] Infections can be transmitted through aquatic organisms which act as a host for the maturity of the parasite.[5] Foodborne trematodiases is transmitted when organisms ingest contaminated undercooked food including aquatic plants and organisms.[2][1]
Trematodiases can be prevented and controlled through public health programs aimed to educate people about how contaminated water and food can lead to infections.[3] Education programs include raising awareness about the transmission of trematodiases through the consumption of food that is not cooked well such as fish, molluscs, and other aquatic animals and plants.[5]Sanitation and distribution of clean water is also used to control the spread of trematodiases on a larger scale.[6]
Most cases of trematodiases show no symptoms.[1] Infected organisms that show symptoms will range in severity depending on number of parasites.[1] When the number of trematodes are high, signs of infection include severe pain in the abdomen.[1] The signs and symptoms of the disease is also impacted by the location and spread of the parasite in the body.[7] Tissues in organs are damaged when infected by the parasite.[3] This damage can be mechanical as the parasite attaches to the walls of the host, as well as chemical.[5]
Symptoms of lung fluke infections (Paragonimus) depend on the parasite’s stage in its life cycle, and how it travels around in the lung.[7][3] Trematodiases that impacts the lungs can cause cough, headache, chest pain, high temperature and change in appetite.[1][5]
Intestinal trematodiases infect the gastrointestinal tract.[10] Symptoms of intestinal fluke infections can range from mild to severe symptoms depending on the length of time that the parasite spends in the body. Signs and symptoms that arise in infected organisms include headache, indigestion problems such as diarrhoea, high temperature and pain in the abdomen which can also lead to malnutrition as the infected organism’s appetite is lost.[10][5] In intestinal trematodiases, the walls of the intestine can be damaged, which can lead to ulcers in some infected organisms.[5]
Trematodiases caused by liver trematodes infect the host’s liver, gall bladder and bile duct and can cause inflammation within these organs.[5][1] Symptoms vary from case to case and include abdominal pain, loss of appetite, problems with indigestion including diarrhoea and constipation, whereas in some cases, no symptoms are shown.[2][5]Opisthorchis viverrini damages the bile duct when in the adult stage of the life cycle, forming the cancer cholangiocarcinoma.[1][5]
Blood flukes can cause the trematodiases schistosomiasis which can cause reactions on skin. When infected, the host can also experience symptoms such as nausea, lack of appetite, diarrhoea and abdominal pain.[4][10]
Causes
Trematodiases are zoonotic infections caused by trematodes.[1] In foodborne trematodiases, these parasites are transferred from animals to humans.[11] Transmission of trematodiases can occur through the consumption of water and food that is contaminated with trematodes in the larval stages of their life cycle.[1] In a host organism, eggs of trematodes can spread through faeces, and sputum if the host is infected by a lung fluke.[7] Once these reach water, they infect aquatic snails which act as intermediate hosts for trematodiases that is transmitted through food.[7][3] A second host will depend on the species of trematode, and are usually aquatic animals[1] Some trematodiases such as schistosomiasis can also be transmitted when skin comes in contact with water containing the parasite.[10] Trematodes all have different life cycles in which they can reproduce asexually and sexually.[4] When trematodes are at the metacercariae stage in their life cycle, humans and other definitive hosts such as mammals and birds can be infected.[7] In humans, adult trematodes can survive for 25 years.[5]
Fasciola hepatica, a species of trematode that causes trematodiases, and infects the liver
Types of trematodiases
There are different types of trematodiases depending on the species of trematode that has infected the organism as well as their location in humans. There are over 80 different species of trematodes that are transmitted through food that can cause infections in humans.[7] Foodborne trematodiases include intestinal flukes, lung flukes and liver flukes.[7] Liver flukes cause liver disease in humans and are caused by the species Clonorchis, Opisthorchis and Fasciola.[2] Intestinal flukes infect the gastrointestinal tract and can be caused by the species such as Fasciolopsis buski, Echinostoma, Metagonimus, Heterophyes, and Gastrodiscoides.[10][5] Lung flukes, mainly the genus, Paragonimus, infect the lungs of organisms, causing infections that can last for up to 20 years in humans.[5][12] Foodborne trematodiases include clonorchiasis, opisthorchiasis, fascioliasis and paragonimiasis.[11]
Diagnosis
Trematodiases can be diagnosed through a variety of methods. One of these is known as parasitological diagnosis, which relies on lab tests that detect the presence of trematode eggs where samples are taken from faeces or sputum.[7][3] Techniques used to measure the number of eggs in samples taken from infected organisms include FLOTAC, Kato-Katz, formalin-ethyl-acetate.[7][3] Different techniques have a different degree in which they can accurately detect eggs of trematodes, and some of these may not be able to detect low amounts.[3] Using a variety of these techniques on different samples can strengthen the accuracy of this method.[3]
Another method in which trematodiases can be diagnosed is through antibodies that are produced by the host’s immune response when infected.[3] This is known as immunodiagnosis. These antibody tests can be highly specific, or not specific at all, depending on the technique used.[3]
Molecular diagnosis is also used to detect trematodiases. This is specific as it uses the methods of polymerase chain reactions, pyrosequencing and other techniques to detect the parasite’s DNA in samples.[7][3] It is suitable for detecting infections regardless of their number.[3][7]
Radiological examinations use imaging such as CT scans, X-rays and ultrasounds to detect certain species of the parasite.[4][3] For liver fluke infections, ultrasounds are commonly used to search for evidence of the infection in the body. It is not very specific in diagnosing the exact trematode which has infected the organism.[5]
Prevention
Species of trematodes that can cause trematodiases
Prevention strategies aim to reduce the number of cases of trematodiases globally and lower infection rates, alongside stopping reinfection of individuals who have been infected before. Public health programs are necessary prevention strategies that aim to raise awareness about the transmission and cause of trematodiases.[1]Food safety and hygiene practices are also implemented to reduce transmission of the parasites through food and water.[3]
Most trematodiases are transmitted through eating raw aquatic plants and animals such as fish, crustaceans, crabs, watercress, frogs and snails.[3] Health education programs aim to outline how transmission of disease can be prevented by raising awareness of food safety practices. This includes spreading information about the importance of heating food to eliminate the chance of contracting trematodiases, as well as the importance of cleaning utensils, cutting boards and other equipment to prevent cross-contamination.[5] These education programs are also used to raise awareness in retailers in order to prevent consumers from infections. The Food and Drug Administration recommends that fish which will be consumed undercooked should be placed in low temperatures and frozen under −20 degrees Celsius for at least a week, or under −35 degrees Celsius for a minimum of 15 hours, as freezing removes any chance of transmitting parasites to consumers.[3]
Data from previous years can also be used to create mathematical models to predict how the disease is transmitted, and where one can effectively intervene in order to stop the increase in cases.[7] Improving access to clean water also helps prevent the transmission of trematodiases through water. Water sanitation and treatment of sewerage are used to prevent the continuation of the cycle of infections.[1][3]
There is no vaccine for foodborne trematodiases that can be used to prevent infections.[5] The World Health Organization has implemented various methods to control the rates of infection by mapping data in endemic areas and reviewing implemented activities by monitoring infection and incidence rates.[1]
Treatment
Chemical structure of Praziquantel, a chemotherapy drug used to treat most forms of trematodiases.
Treatment varies depending on the number of cases in an area. Chemotherapy drugs praziquantel and triclabendazole can be used in different amounts depending on the type of trematode infecting the organism, and its location in the body.[1][3] 600,000 cases globally received treatment for foodborne trematodiases in 2016.[1]
Praziquantel can act on a broad range of trematodes by disrupting the homeostasis of calcium ions, and is used to treat liver, intestinal and lung fluke infections.[3] It was introduced as a treatment option in 1975 and targets various trematodiases by impacting the trematode’s ability to move in the host.[13] Adverse reactions to this treatment that may occur are mild, and include headache, abdominal pain and dizziness.[13] Although it is very effective and safe in treating most trematodiases, praziquantel can cause hypersensitivity or allergic reactions in rare cases. It also cannot be used to treat the trematodiasis fascioliasis.[13]
Triclabendazole is a narrow-spectrum treatment of trematodiases and is commonly used to treat fascioliasis.[14] This anthelminthic is effective against the species Fasciola and Paragonimus. Although it was used in domestic livestock from 1983, the treatment was only approved for use in humans in 1997 in Egypt.[14] In 2019, it was approved by the US Food and Drug Administration for treating cases of human infections.[14] Common adverse reactions to triclabendazole include dizziness, sweating, pain in abdomen, headaches and biliary colic, which is mainly caused by the removal of dead trematodes from the body’s hepatobiliary system.[14]
Preventive chemotherapy is a strategy used in areas where the number of cases and infection rates are very high, as all individuals in the given area are treated with medicine for trematodiases.[1] This is used as an option to prevent further spread of the infection. For clonorchiasis and opisthorchiasis, when the incidence of cases exceeds 20%, all individuals are treated every year.[1]
Epidemiology
Trematodiases that infect the lung, liver and intestine are classified as neglected tropical diseases by the World Health Organization.[6] Neglected tropical diseases are made up of bacterial, parasitic and viral infections that negatively impact the development of children, pregnancy and economic outcomes of developing countries.[6]
Changes in population numbers, food distribution channels, poverty and health education programs contribute to the fluctuating epidemiological patterns.[3] Social, ecological and economic factors also change distribution patterns globally. Factors such as rainfall, pollution, climate, vegetation, water temperature and quality change the interactions between trematodes and their hosts.[7] The expansion of aquaculture production and irrigation systems has also changed the spread of the disease. In areas where water is not sufficiently sanitised, infection rates have increased.[7]
The World Health Organization declares that there are approximately 200,000 cases per year, leading to over 7000 deaths.[1] The highest number of foodborne trematodiasis cases and the highest disease burden were recorded in East and Southeast Asia in 2019.[7] In northeast Thailand, [[Opisthorchis viverrini, which is carcinogenic, is present in high numbers, and over 20,000 lives are lost a year due to cholangiocarcinoma caused by the trematode.[7]
Clonorchis sinesis, a species which causes trematodiases that infect the liver
Clonorchis sinensis and Opisthorchis viverrini are two species which can cause trematodiases that infect the liver. These are more prevalent in males than females, and more common in adults than children.[5] Fasciola hepatica, a species of liver flukes, has a higher incidence rate in children and females, with more cases of lung fluke and intestinal trematodiases in children.[5] Cases of liver and lung fluke trematodiasis are frequent due to the length of time the trematode can live in host organisms, and increased chances of reinfection.[7]
Increase in travel and increase in popularity of traditional dishes such as raw oysters, crab meat, pickled seafood and other undercooked aquatic plants have also contributed to the rise in cases of trematodiases.[7] The Global Burden of Disease Study carried out in 2016 estimated that approximately 75 million people were impacted by trematodiases and around 2 million disability-adjusted life years were lost to the disease, due to damage caused by the infection.[7]
Related Research Articles
Trematoda is a class of flatworms known as flukes or trematodes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host, where the flukes sexually reproduce, is a vertebrate. Infection by trematodes can cause disease in all five traditional vertebrate classes: mammals, birds, amphibians, reptiles, and fish.
Clonorchis sinensis, the Chinese liver fluke, is a liver fluke belonging to the class Trematoda, phylum Platyhelminthes. It infects fish-eating mammals, including humans. In humans, it infects the common bile duct and gall bladder, feeding on bile. It was discovered by British physician James McConnell at the Medical College Hospital in Calcutta (Kolkata) in 1874. The first description was given by Thomas Spencer Cobbold, who named it Distoma sinense. The fluke passes its lifecycle in three different hosts, namely freshwater snail as first intermediate hosts, freshwater fish as second intermediate host, and mammals as definitive hosts.
Clonorchiasis is an infectious disease caused by the Chinese liver fluke and two related species. Clonorchiasis is a known risk factor for the development of cholangiocarcinoma, a neoplasm of the biliary system.
Fasciolosis is a parasitic worm infection caused by the common liver fluke Fasciola hepatica as well as by Fasciola gigantica. The disease is a plant-borne trematode zoonosis, and is classified as a neglected tropical disease (NTD). It affects humans, but its main host is ruminants such as cattle and sheep. The disease progresses through four distinct phases; an initial incubation phase of between a few days up to three months with little or no symptoms; an invasive or acute phase which may manifest with: fever, malaise, abdominal pain, gastrointestinal symptoms, urticaria, anemia, jaundice, and respiratory symptoms. The disease later progresses to a latent phase with less symptoms and ultimately into a chronic or obstructive phase months to years later. In the chronic state the disease causes inflammation of the bile ducts, gall bladder and may cause gall stones as well as fibrosis. While chronic inflammation is connected to increased cancer rates, it is unclear whether fasciolosis is associated with increased cancer risk.
Fasciolopsiasis results from an infection by the trematode Fasciolopsis buski, the largest intestinal fluke of humans, growing up to 7.5 cm (3.0 in) long.
Metagonimiasis is a disease caused by an intestinal trematode, most commonly Metagonimus yokagawai, but sometimes by M. takashii or M. miyatai. The metagonimiasis-causing flukes are one of two minute flukes called the heterophyids. Metagonimiasis was described by Katsurasa in 1911–1913 when he first observed eggs of M. yokagawai in feces. M. takahashii was described later first by Suzuki in 1930 and then M. miyatai was described in 1984 by Saito.
Fasciola hepatica, also known as the common liver fluke or sheep liver fluke, is a parasitic trematode of the class Trematoda, phylum Platyhelminthes. It infects the livers of various mammals, including humans, and is transmitted by sheep and cattle to humans all over the world. The disease caused by the fluke is called fasciolosis or fascioliasis, which is a type of helminthiasis and has been classified as a neglected tropical disease. Fasciolosis is currently classified as a plant/food-borne trematode infection, often acquired through eating the parasite's metacercariae encysted on plants. F. hepatica, which is distributed worldwide, has been known as an important parasite of sheep and cattle for decades and causes significant economic losses in these livestock species, up to £23 million in the UK alone. Because of its relatively large size and economic importance, it has been the subject of many scientific investigations and may be the best-known of any trematode species. F. hepatica's closest relative is Fasciola gigantica. These two flukes are sister species; they share many morphological features and can mate with each other.
Fasciola, commonly known as the liver fluke, is a genus of parasitic trematodes. There are three species within the genus Fasciola: Fasciola nyanzae,Fasciolahepatica and Fasciolagigantica. Fasciola hepatica and F. gigantica are known to form hybrids. Both F. hepatica and F. gigantica and their hybrids 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. Fasciola nyanzae is thought to exclusively infect the common hippopotamus, Hippopotamus amphibius.
Paragonimus westermani is the most common species of lung fluke that infects humans, causing paragonimiasis. Human infections are most common in eastern Asia and in South America. Paragonimiasis may present as a sub-acute to chronic inflammatory disease of the lung. It was discovered by Coenraad Kerbert (1849–1927) in 1878.
Opisthorchis viverrini, common name Southeast Asian liver fluke, is a food-borne trematode parasite from the family Opisthorchiidae that infects the bile duct. People are infected after eating raw or undercooked fish. Infection with the parasite is called opisthorchiasis. O. viverrini infection also increases the risk of cholangiocarcinoma, a cancer of the bile ducts.
Paragonimus is a genus of flukes (trematodes) and is the only genus in the monotypic family Paragonimidae. Some tens of species have been described, but they are difficult to distinguish, so it is not clear how many of the named species may be synonyms. The name Paragonimus is derived from the combination of two Greek words, “para” and “gonimos”. Several of the species are known as lung flukes. In humans some of the species occur as zoonoses; the term for the condition is paragonimiasis. The first intermediate hosts of Paragonimus include at least 54 species of freshwater snails from superfamilies Cerithioidea and Rissooidea.
Paragonimiasis is a food-borne parasitic disease caused by several species of lung flukes belonging to genus Paragonimus. Infection is acquired by eating crustaceans such as crabs and crayfishes which host the infective forms called metacercariae, or by eating raw or undercooked meat of mammals harboring the metacercariae from crustaceans.
Dicrocoelium dendriticum, the lancet liver fluke, is a parasite fluke that tends to live in cattle or other grazing mammals.
Opisthorchis felineus, the Siberian liver fluke or cat liver fluke, is a trematode parasite that infects the liver in mammals. It was first discovered in 1884 in a cat's liver by Sebastiano Rivolta of Italy. In 1891, Russian parasitologist, Konstantin Nikolaevich Vinogradov (1847–1906) found it in a human, and named the parasite a "Siberian liver fluke". In the 1930s, helminthologist Hans Vogel of Hamburg published an article describing the life cycle of Opisthorchis felineus. Felineus infections may also involve the pancreatic ducts. Diagnosis of Opisthorchis infection is based on microscopic identification of parasite eggs in stool specimens. Safe and effective medication is available to treat Opisthorchis infections. Adequately freezing or cooking fish will kill the parasite.
Opisthorchiasis is a parasitic disease caused by certain species of genus Opisthorchis. Chronic infection may lead to cholangiocarcinoma, a cancer of the bile ducts.
Liver fluke is a collective name of a polyphyletic group of parasitic trematodes under the phylum Platyhelminthes. They are principally parasites of the liver of various mammals, including humans. Capable of moving along the blood circulation, they can occur also in bile ducts, gallbladder, and liver parenchyma. In these organs, they produce pathological lesions leading to parasitic diseases. They have complex life cycles requiring two or three different hosts, with free-living larval stages in water.
Fasciolopsis is a genus of trematodes. They are also known as giant intestinal flukes.
Heterophyes heterophyes, or the intestinal fish fluke, was discovered by Theodor Maximaillian Bilharz in 1851. This parasite was found during an autopsy of an Egyptian mummy. H. heterophyes is found in the Middle East, West Europe and Africa. They use different species to complete their complex lifestyle. Humans and other mammals are the definitive host, first intermediate host are snails, and second intermediate are fish. Mammals that come in contact with the parasite are dogs, humans, and cats. Snails that are affected by this parasite are the Cerithideopsilla conica. Fish that come in contact with this parasite are Mugil cephalus, Tilapia milotica, Aphanius fasciatus, and Acanthgobius sp. Humans and mammals will come in contact with this parasite by the consumption of contaminated or raw fish. This parasite is one of the smallest endoparasite to infect humans. It can cause intestinal infection called heterophyiasis.
Carcinogenic parasites are parasitic organisms that depend on other organisms for their survival, and cause cancer in such hosts. Three species of flukes (trematodes) are medically-proven carcinogenic parasites, namely the urinary blood fluke, the Southeast Asian liver fluke and the Chinese liver fluke. S. haematobium is prevalent in Africa and the Middle East, and is the leading cause of bladder cancer. O. viverrini and C. sinensis are both found in eastern and southeastern Asia, and are responsible for cholangiocarcinoma. The International Agency for Research on Cancer declared them in 2009 as a Group 1 biological carcinogens in humans.
Gastropod-borne parasitic diseases (GPDs) are a group of infectious diseases that require a gastropod species to serve as an intermediate host for a parasitic organism that can infect humans upon ingesting the parasite or coming into contact with contaminated water sources. These diseases can cause a range of symptoms, from mild discomfort to severe, life-threatening conditions, with them being prevalent in many parts of the world, particularly in developing regions. Preventive measures such as proper sanitation and hygiene practices, avoiding contact with infected gastropods and cooking or boiling food properly can help to reduce the risk of these diseases.
1 2 3 4 5 Pottinger, Paul S.; Jong, Elaine C. (2017-01-01), Sanford, Christopher A.; Pottinger, Paul S.; Jong, Elaine C. (eds.), "Chapter 48 - Trematodes", The Travel and Tropical Medicine Manual (Fifth Edition), Elsevier, pp.588–597, doi:10.1016/b978-0-323-37506-1.00048-9, ISBN978-0-323-37506-1
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