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Manifestation, diagnosis, and management of foodborne trematodiasis
Abstract and Figures
#### Summary points
Foodborne trematodiasis is a cluster of zoonotic infections caused by parasitic worms (class: trematoda; also known as flukes), which are transmitted via the ingestion of contaminated, mainly aquatic, food. More than one billion people are at risk of infection according to a systematic review from 2005.1 Another systematic review and meta-analysis suggests that 56 million people were infected in 2005, mainly in Asia and Latin America, with a global burden of 665 000 disability adjusted life years.2
Depending on the fluke species, foodborne trematodiasis is associated with a variety of signs, symptoms, and pathological consequences. The non-specificity of the clinical manifestations, the wide range of fluke species, and shortcomings in current diagnostic techniques are some of the reasons why foodborne trematodiasis is underestimated.3 4
This review introduces the most important foodborne trematode species and describes their geographical distribution. It also discusses pathological consequences, clinical manifestations, diagnosis, …
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... In the Philippines, two cases were initially reported that were thought to be caused by consumption of improperly prepared kangkong (Ipomoea aquatica) or other water vegetables ( Figure 1B) (Eduardo, 2001). In both humans and animals, fasciolosis occurs in two phases: acute or invasive phase and chronic or latent phase (Fürst et al., 2012b, Leerapun et al., 2021 Acute fasciolosis symptoms occur due to the migration of immature flukes, while liver abscesses leading to the development 'pipestem' fibrosis are seen in chronic cases (Fürst et al., 2012b;Leerapun et al., 2021). A recent study found that abdominal pain, weight loss and fever were the most common symptoms encountered by patients with hepatic abscesses due to fasciolosis (Leerapun et al., 2021). ...
... In the Philippines, two cases were initially reported that were thought to be caused by consumption of improperly prepared kangkong (Ipomoea aquatica) or other water vegetables ( Figure 1B) (Eduardo, 2001). In both humans and animals, fasciolosis occurs in two phases: acute or invasive phase and chronic or latent phase (Fürst et al., 2012b, Leerapun et al., 2021 Acute fasciolosis symptoms occur due to the migration of immature flukes, while liver abscesses leading to the development 'pipestem' fibrosis are seen in chronic cases (Fürst et al., 2012b;Leerapun et al., 2021). A recent study found that abdominal pain, weight loss and fever were the most common symptoms encountered by patients with hepatic abscesses due to fasciolosis (Leerapun et al., 2021). ...
Foodborne trematodiasis is a neglected tropical disease (NTD) caused by zoonotic trematodes that persist mainly in impoverished areas in the Asia-Pacific region. Globally, about 2 million disability life years (DALYs) are lost due to these parasitic infections. Four groups of foodborne trematodes are known to cause significant illness: fish-borne liver fluke infections caused by Opisthorchis and Clonorchis spp.; water vegetable-borne Fasciola spp. infections; crustacean-vectored paragonimiasis; and those caused by intestinal trematodes. In the Philippines, endemic foodborne trematodes of public health concern include Paragonimus westermani, some members of Heterophyidae and Echinostomatidae, and Fasciola hepatica/ F. gigantica. Opisthorchis viverrini and Clonorchis sinensis have also been reported in the country. Data on the epidemiology of these zoonotic illnesses remain scarce and in need of research attention in the Philippines. Culturally rooted eating behaviors in endemic areas are important risk factors to acquiring and perpetuating foodborne trematodiasis. The combination of mass drug administration (MDA), provision of clean water and maintenance of good sanitation and hygiene (WASH), community health education towards modification of risky behaviors, surveillance, and veterinary public health interventions have been shown to be effective in combatting these zoonotic parasitoses. An integrated control and prevention program anchored on the One Health paradigm is a must to address these illnesses. This paper aims to review the biology and epidemiology of, and public health interventions against zoonotic foodborne trematodiasis in the Philippines and its neighboring countries.
... In the Philippines, two cases were initially reported that were thought to be caused by consumption of improperly prepared kangkong (Ipomoea aquatica) or other water vegetables ( Figure 1B) (Eduardo, 2001). In both humans and animals, fasciolosis occurs in two phases: acute or invasive phase and chronic or latent phase (Fürst et al., 2012b, Leerapun et al., 2021 Acute fasciolosis symptoms occur due to the migration of immature flukes, while liver abscesses leading to the development 'pipestem' fibrosis are seen in chronic cases (Fürst et al., 2012b;Leerapun et al., 2021). A recent study found that abdominal pain, weight loss and fever were the most common symptoms encountered by patients with hepatic abscesses due to fasciolosis (Leerapun et al., 2021). ...
... In the Philippines, two cases were initially reported that were thought to be caused by consumption of improperly prepared kangkong (Ipomoea aquatica) or other water vegetables ( Figure 1B) (Eduardo, 2001). In both humans and animals, fasciolosis occurs in two phases: acute or invasive phase and chronic or latent phase (Fürst et al., 2012b, Leerapun et al., 2021 Acute fasciolosis symptoms occur due to the migration of immature flukes, while liver abscesses leading to the development 'pipestem' fibrosis are seen in chronic cases (Fürst et al., 2012b;Leerapun et al., 2021). A recent study found that abdominal pain, weight loss and fever were the most common symptoms encountered by patients with hepatic abscesses due to fasciolosis (Leerapun et al., 2021). ...
Foodborne trematodiasis is a neglected tropical disease (NTD) caused by zoonotic trematodes that persist mainly in impoverished areas in the Asia-Pacific region. Globally, about 2 million disability life years (DALYs) are lost due to these parasitic infections. Four groups of foodborne trematodes are known to cause significant illness: fish-borne liver fluke infections caused by Opisthorchis and Clonorchis spp.; water vegetable-borne Fasciola spp. infections; crustacean-vectored paragonimiasis; and those caused by intestinal trematodes. In the Philippines, endemic foodborne trematodes of public health concern include Paragonimus westermani, some members of Heterophyidae and Echinostomatidae, and Fasciola hepatica/ F. gigantica. Opisthorchis viverrini and Clonorchis sinensis have also been reported in the country. Data on the epidemiology of these zoonotic illnesses remain scarce and in need of research attention in the Philippines. Culturally rooted eating behaviors in endemic areas are important risk factors to acquiring and perpetuating foodborne trematodiasis. The combination of mass drug administration (MDA), provision of clean water and maintenance of good sanitation and hygiene (WASH), community health education towards modification of risky behaviors , surveillance, and veterinary public health interventions have been shown to be effective in combatting these zoonotic parasitoses. An integrated control and prevention program anchored on the One Health paradigm is a must to address these illnesses. This paper aims to review the biology and epidemiology of, and public health interventions against zoonotic foodborne trematodiasis in the Philippines and its neighboring countries.
... Research has shown that F. hepatica is more common in high and mountainous areas, while F. gigantica is more common in lower areas, depending on the distribution of the intermediate snail [6,7]. Controlling the population of intermediate snail hosts can be considered a suitable strategy to reduce the endemicity of food-borne trematode infections, especially fascioliasis [8][9][10]. This issue shows the importance of investigating the influence of geographical factors on the distribution of intermediate snail hosts and their infection rate. ...
Background
Snails of the Lymnaeidae family are the intermediate hosts of Fasciola species, the causative agents of fascioliasis. The purpose of this study was to determine the prevalence of Fasciola species in lymnaeid snails and to investigate the association of geoclimatic factors and Fasciola species distribution in northwestern provinces of Iran using geographical information system (GIS) data.
Methods
A total of 2000 lymnaeid snails were collected from 33 permanent and seasonal habitats in northwestern Iran during the period from June to November 2021. After identification by standard morphological keys, they were subjected to shedding and crushing methods. Different stages of Fasciola obtained from these snails were subjected to the ITS1 polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) method for species identification. The associations of weather temperature, rainfall, humidity, evaporation, air pressure, wind speed, elevation, and land cover with the distribution of Fasciola species were investigated. Geographical and statistical analysis was performed using ArcMap and SPSS software, respectively, to determine factors related to Fasciola species distribution.
Results
Of the 2000 snails collected, 19 were infected with Fasciola hepatica (0.09%), six with F. gigantica (0.03%), and 13 with other trematodes. Among geoclimatic and environmental factors, mean humidity, maximum humidity, and wind speed were significantly higher in areas where F. hepatica was more common than F. gigantica. The altitude of F. hepatica-prevalent areas was generally lower than F. gigantica areas. No significant relationship was observed between other investigated geoclimatic factors and the distribution of infected snails.
Conclusions
The present study showed the relationship of humidity and wind speed with the distribution of snails infected with F. hepatica or F. gigantica in the northwestern regions of Iran. In contrast to F. gigantica, F. hepatica was more prevalent in low-altitude areas. Further research is recommended to elucidate the relationship between geoclimatic factors and the presence of intermediate hosts of the two Fasciola species.
Graphical Abstract
... The gold standard for diagnosing trematode infection involves examining fecal eggs, which can be performed through ether concentration, sedimentation techniques, or the Kato-Katz method. In the case of visceral inspection, the presence of worms in the liver can also be used (13)(14)(15)(16). FBT infections are usually diagnosed through imaging, immunodiagnostic, and molecular techniques (humans), as well as parasitological methods (animals). ...
Fasciola hepatica can cause problems in both animals and humans. Fasciolosis can be diagnosed through the indirect ELISA immunodiagnostic test. Serological diagnosis of Fasciola is based on recombinant antigens secreted by this worm. We used PubMed and Google Scholar databases to review the published literature on ‘antigens with immunogenic potential’ used in serological tests to identify antibodies against F. hepatica in humans, cattle, and sheep. Studies that investigated diagnostic tests with common reference standards were included in the sensitivity and/or specificity bivariate meta-analysis. In the quality and susceptibility to bias analysis of the 33 included studies, 26 fulfilled at least six (75%) of the eight QUADAS criteria and were considered good-quality papers. We found that most of the studies used native excretory-secretory antigens and recombinant cathepsin in ELISA tests for serological diagnosis of fascioliasis in humans, cattle, and sheep. The meta-analysis revealed that all antigens demonstrated good accuracy. The best results in terms of sensitivity [0.931–2.5% confidence interval (CI) and 0.985–97.5% CI] and specificity (0.959–2.5% CI and 0.997–97.5% CI) were found in human FhES. FhrCL-1, FhES, and FhrSAP-2 antigens gave the best results for the serum diagnosis of human and animal fasciolosis.
... The cysts (metacercariae) are then ingested by the final human host and develop into hermaphroditic adults in either the liver, lungs or the intestines. Eggs are passed in the sputum (lung flukes), stool or urine [27,44]. Annually, foodborne trematodes infect 200,000 people, cause 7000 deaths and create a burden of more than 2 million DALYs [42]. ...
Helminths, with an estimated 1.5 billion annual global infections, are one of the major health challenges worldwide. The current strategy of the World Health Organization to prevent helminth infection includes increasing hygienic awareness, providing better sanitation and preventative anthelmintic drug therapy in vulnerable populations. Nowadays, anthelmintic drugs are used heavily in livestock, both in case of infection and as a preventative measure. However, this has led to the development of resistance against several of the most common drugs, such as levamisole, ivermectin and thiabendazole. As many as 70% of the livestock in developed countries now has helminths that are drug resistant, and multiple resistance is common. Because of this, novel anthelmintics are urgently needed to help combat large-scale production losses. Prior to this review, no comprehensive review of the anthelmintic effects of essential oils and their components existed. Multiple review articles have been published on the uses of a single plant and its extracts that only briefly touch upon their anthelmintic activity. This review aims to provide a detailed overview of essential oils and their components as anthelmintic treatment against a wider variety of helminths.
... Opisthorchiasis affects more than 8 million people in Southeast Asia and is caused by the trematode Opisthorchis viverrini via consumption of raw or undercooked fish. In the early phase, the disease is generally asymptomatic, but, in its chronic stage, patients can suffer severe symptoms from gallstone formation and periductal fibrosis to obstructing jaundice, ascending cholangitis and eventually develop a cholangiocarcinoma [3][4][5]. ...
Racemic praziquantel (PZQ) is the standard treatment for schistosomiasis and liver fluke infections (opisthorchiasis and clonorchiasis). The development of an optimal pediatric formulation and dose selection would benefit from a population pharmacokinetic (popPK) model. A popPK model was developed for R-PZQ, the active enantiomer of PZQ, in 664 subjects, 493 African children (2–15 years) infected with Schistosoma mansoni and S. haematobium, and 171 Lao adults (15–78 years) infected with Opisthorchis viverrini. Racemate tablets were administered as single doses of 20, 40 and 60 mg/kg in children and 30, 40 and 50 mg/kg in 129 adults, and as 3 × 25 mg/kg apart in 42 adults. Samples collected by the dried-blood-spot technique were assayed by LC-MS/MS. A two-compartment disposition model, with allometric scaling and dual first-order and transit absorption, was developed using Phoenix™ software. Inversely parallel functions of age described the apparent oral bioavailability (BA) and clearance maturation in children and ageing in adults. BA decreased slightly in children with dose increase, and by 35% in adults with multiple dosing. Crushing tablets for preschool-aged children increased the first-order absorption rate by 64%. The mean transit absorption time was 70% higher in children. A popPK model for R-PZQ integrated African children over 2 years of age with schistosomiasis and Lao adults with opisthorchiasis, and should be useful to support dose optimization in children. In vitro hepatic and intestinal metabolism data would help refining and validating the model in younger children as well as in target ethnic pediatric and adult groups.
Objectives
Optical fluorescence imaging can track the biodistribution of fluorophore-labeled drugs, nanoparticles, and antibodies longitudinally. In hybrid computed tomography–fluorescence tomography (CT-FLT), CT provides the anatomical information to generate scattering and absorption maps supporting a 3-dimensional reconstruction from the raw optical data. However, given the CT's limited soft tissue contrast, fluorescence reconstruction and quantification can be inaccurate and not sufficiently detailed. Magnetic resonance imaging (MRI) can overcome these limitations and extend the options for tissue characterization. Thus, we aimed to establish a hybrid CT-MRI-FLT approach for whole-body imaging and compared it with CT-FLT.
Materials and Methods
The MRI-based hybrid imaging approaches were established first by scanning a water and coconut oil–filled phantom, second by quantifying Cy7 concentrations of inserts in dead mice, and finally by analyzing the biodistribution of AF750-labeled immunoglobulins (IgG, IgA) in living SKH1 mice. Magnetic resonance imaging, acquired with a fat-water–separated mDixon sequence, CT, and FLT were co-registered using markers in the mouse holder frame filled with white petrolatum, which was solid, stable, and visible in both modalities.
Results
Computed tomography–MRI fusion was confirmed by comparing the segmentation agreement using Dice scores. Phantom segmentations showed good agreement, after correction for gradient linearity distortion and chemical shift. Organ segmentations in dead and living mice revealed adequate agreement for fusion. Marking the mouse holder frame and the successful CT-MRI fusion enabled MRI-FLT as well as CT-MRI-FLT reconstructions. Fluorescence tomography reconstructions supported by CT, MRI, or CT-MRI were comparable in dead mice with 60 pmol fluorescence inserts at different locations. Although standard CT-FLT reconstruction only considered general values for soft tissue, skin, lung, fat, and bone scattering, MRI's more versatile soft tissue contrast enabled the additional consideration of liver, kidneys, and brain. However, this did not change FLT reconstructions and quantifications significantly, whereas for extending scattering maps, it was important to accurately segment the organs and the entire mouse body. The various FLT reconstructions also provided comparable results for the in vivo biodistribution analyses with fluorescent immunoglobulins. However, MRI additionally enabled the visualization of gallbladder, thyroid, and brain. Furthermore, segmentations of liver, spleen, and kidney were more reliable due to better-defined contours than in CT. Therefore, the improved segmentations enabled better assignment of fluorescence signals and more differentiated conclusions with MRI-FLT.
Conclusions
Whole-body CT-MRI-FLT was implemented as a novel trimodal imaging approach, which allowed to more accurately assign fluorescence signals, thereby significantly improving pharmacokinetic analyses.
Background
Clonorchis sinensis, Opisthorchis viverrini, and Opisthorchis felineus are the three most important human liver fluke species in the Opisthorchiidae family, infecting approximately 25 million people worldwide. Drug treatment is needed to control morbidity and is also useful in lowering transmission. Several drugs used in various regimens are available to treat these infections, but their comparative efficacy is uncertain. We aimed to compare the efficacy in terms of cure rate and egg reduction rate of currently registered drugs against human liver fluke infection.
Methods
We conducted a systematic review using readily available electronic databases (MEDLINE, Embase, Cochrane Central Register of Controlled Trials, KoreaMed, China National Knowledge Infrastructure, and Wanfang Data) without language restrictions from inception until June 29, 2021. Clinical trials with pairwise comparison of drugs (praziquantel, albendazole, mebendazole, tribendimidine, or combinations of these drugs) against C sinensis, O viverrini, and O felineus were eligible, including trials comparing these drugs or their combinations with placebo. We compared efficacy in terms of cure rate by network meta-analysis. We conducted mixed binomial regression analyses for each species to derive predicted median cure rates for each drug regimen. The models included treatment and infection intensity as fixed factors, year of publication as covariate, and random effects of the different studies assumed to be normally distributed. We also assessed the quality of the included studies. This study was registered with PROSPERO (CRD42018109232).
Findings
Overall, 26 trials from 25 studies were included, of which 18 involved C sinensis, seven studied O viverrini, and one focused on O felineus. These trials included a total of 3340 participants. The two long-term treatment courses against C sinensis infection using 400 mg of albendazole (400 mg twice a day for 5 days and 400 mg twice a day for 7 days) resulted in cure rates of 100%, while two other multiple-dose regimens of albendazole resulted in high predicted cure rates: 300 mg twice a day for 5 days (93·9% [95% CI 49·6–99·6]) and 400 mg twice a day for 3 days (91·0% [50·9–99·0]). The WHO-recommended praziquantel regimen (25 mg/kg three times a day for 2 days) also showed a high predicted cure rate (98·5% [85·4–99·9]) in C sinensis infection, and predicted cure rates were above 90% for several other multiple-dose praziquantel regimens, including 20 mg/kg three times a day for 3 days (97·6% [74·7–99·8]), 14 mg/kg three times a day for 5 days (93·9% [44·8–99·7]), and 20 mg/kg twice a day for 3 days (91·0% [50·9–99·0]). In O viverrini infection, the regimen of 50 mg/kg and 25 mg/kg of praziquantel given in a single day showed the highest predicted cure rate (93·8% [85·7–97·5]), while a single dose of 50 mg/kg praziquantel also resulted in a high predicted cure rate (92·1% [64·9–98·6]). The single dose of 400 mg tribendimidine showed a high predicted cure rate of 89·8% (77·5–95·8). A low quality of evidence was demonstrated in most studies, especially those published before 2000. Selection bias due to poor random sequence generation and allocation concealment was high, and performance and detection biases were frequently unreported.
Interpretation
Praziquantel shows high efficacy against clonorchiasis and opisthorchiasis. Tribendimidine might serve as a treatment alternative and warrants further investigation. Although albendazole is efficacious when long treatment schedules (5 days or 7 days) are applied, limited size of studies and high risk of bias affect the interpretation of results. More high-quality studies are needed to promote the establishment of treatment guidelines for human liver fluke infection.
Funding
Fourth Round of Three-Year Public Health Action Plan (2015–2017; Shanghai, China) and Swiss National Science Foundation.
Foodborne trematodes (FBT) of public health significance include liver flukes (Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Fasciola hepatica and F. gigantica), lung flukes (Paragonimus westermani and several other Paragonimus spp.) and intestinal flukes, which include heterophyids (Metagonimus yokogawai, Heterophyes nocens and Haplorchis taichui), echinostomes (Echinostoma revolutum, Isthmiophora hortensis, Echinochasmus japonicus and Artyfechinostomum malayanum) and miscellaneous species, including Fasciolopsis buski and Gymnophalloides seoi. These trematode infections are distributed worldwide but occur most commonly in Asia. The global burden of FBT diseases has been estimated at about 80 million, however, this seems to be a considerable underestimate. Their life cycle involves a molluscan first intermediate host, and a second intermediate host, including freshwater fish, crustaceans, aquatic vegetables and freshwater or brackish water gastropods and bivalves. The mode of human infection is the consumption of the second intermediate host under raw or improperly cooked conditions. The major pathogenesis of C. sinensis and Opisthorchis spp. infection includes inflammation of the bile duct which leads to cholangitis and cholecystitis, and in a substantial number of patients, serious complications, such as liver cirrhosis and cholangiocarcinoma, may develop. In lung fluke infections, cough, bloody sputum and bronchiectasis are the most common clinical manifestations. However, lung flukes often migrate to extrapulmonary sites, including the brain, spinal cord, skin, subcutaneous tissues and abdominal organs. Intestinal flukes can induce inflammation in the intestinal mucosa, and they may at times undergo extraintestinal migration, in particular, in immunocompromised patients. In order to control FBT infections, eating foods after proper cooking is strongly recommended.
Tribendimidine (TBD) is a broad-spectrum anthelmintic drug that is also significantly effective in treating clonorchiasis. In this study, the altered metabolomes of Clonorchis sinensis (C. sinensis) in rats after TBD administration were quantified by using ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC–MS/MS) and gas chromatography-mass spectrometry (GC–MS) to explore the possible active sites of TBD against clonorchiasis through altered metabolites and metabolic pathway analysis, and the results are expected to provide a target for the future design of anti-Clonorchis sinensis drugs. The worm burden reduction rate and scanning electron microscopy demonstrated that praziquantel (PZQ, positive control drug) and TBD had significant effects on C. sinensis in rats after treatment at a single dose of 200 mg/kg for 24 h. For the MS-based metabolomic analysis, a total of 173 standard metabolites (126 amino acids, 10 phospholipids and 37 fatty acids) were utilized as a reference metabolite database for metabolome identification. In total, 32 amino acids, 71 phospholipids and 27 fatty acids were detected in the C. sinensis of each group. Among these metabolites, 10 amino acids were significantly decreased in both drug-treated groups. Four lysophosphatidyl cholines (LPCs), six lysophosphatidyl ethanolamines (LPEs) and one phosphatidyl inositol (PI) were significantly increased after treatment with TBD. There were no significant changes in fatty acids among the control group and the two drug-treated groups. The results indicated that TBD administration caused a decrease in amino acids involved in the metabolic pathways of energy consumption and an increase in lysophospholipids, which are the hydrolysis products of phospholipase2 (PLA2) in the phospholipid metabolic pathways. The increased lysophospholipid content can destroy the cell membrane, increase membrane permeability, and even cause exposure to internal antigens that can be attacked by host antibodies. Perhaps the destroyed membrane, the exposed internal antigens and the consumed energy are the cause of the damage and death of C. sinensis after TBD administration. This is an interesting problem that can be examined in future research.
Background:
The aim of this study was to determine the effect of metronidazole in patients who did not cure after treatment with triclabendazole, in Guilan (Northern Province of Iran).
Material/methods:
Patients, who passed fasciola egg in stool and had positive serum anti fasciola antibody (ELISA), at least three months after treatment with triclabendazole, were enrolled and received 1.5 g/day metronidazole orally for three weeks. Two months and 12 months after end of therapy, stool examination in 3 consecutive days and serum anti fasciola antibody were performed. Frequency of patients with negative serology for fasciola and/or absence of fasciola egg in stool were determined. Chi-square test was used and P value <0.05 was considered significant.
Results:
Forty-six patients, 26 females and 20 males, were enrolled with mean (+/-SD) age of 34.6(+/-9.8) years. Three patients excluded because of drug side effect and poor compliance. Two months after end of therapy, stool exam became negative in 35 patients and in 31 patients became negative both in serology and stool examination. (Difference in response to treat between age groups and genders was not significant). All patients with abdominal pain became pain free after therapy. Most frequent side effects were metallic taste in 14 (30.4%), headache in 8 (17.4%) and nausea in 6 (13%). 12 months after end of therapy, 28 out of 35 patients were examined again and all were negative both in serology and egg in stool examination.
Conclusions:
Metronidazole, 1.5 g/day for 3 weeks, seems to be an effective, available, well-tolerated alternative for treatment of human fascioliasis.
The food-borne trematodiases are an important group of neglected tropical diseases (NTDs). Over 40 million people are infected with food-borne trematodes and 750 million (>10% of the world's population) are at risk of these NTDs. Here, we review the life cycles, epidemiology, clinical manifestations, pathology and pathogenesis, diagnosis, treatment, and prevention and control of the major food-borne trematodiases in Southeast Asia. We focus particularly on opisthorchiasis caused by Opisthorchis viverrini and clonorchiasis caused by Clonorchis sinensis, which people contract by ingestion of metacercariae in flesh of raw or undercooked freshwater fishes, on fascioliasis caused by Fasciola species, where infection arises from ingestion of metacercariae on water plants such as watercress, and on Paragonimus species, the lung flukes, which use freshwater crabs and other crustaceans as intermediate hosts. We also include information on the intestinal flukes Fasciolopsis buski, the echinostomes and the so-called ‘minute intestinal flukes’ of the family Heterophyidae. Ecological information, placing emphasis on reservoir hosts, intermediate snail hosts and secondary hosts where applicable, is also reviewed and research needs are highlighted.
Around the world, 40 to 50 million people are currently estimated to be infected with food-borne intestinal trematodes (Fried
et al., 2004), including at least 18 million people infected by fish-borne trematodes (Chai et al., 2005a). However, this
may be an underestimate of the total number of humans infected. The number of trematode species, currently known to be involved,
is 70 (Yu and Mott, 1994; Chai and Lee, 2002).
Food-borne trematodes (FBTs) contribute to parasitic zoonoses such as liver, lung, and intestinal flukes of humans and they
are contracted by the consumption of larval stages in food-related products. Food-borne trematodiasis has been recognized
as an important health problem in Asia (WHO, 1995, 2004). The infections are prevalent in developing countries and are closely
linked to poverty, pollution, and population growth, and are also associated with cultural determinants, that is, food behavior
and tradition.
There are six plant-borne trematode species known affecting humans: Fasciola hepatica, F. gigantica, and Fasciolopsis buski
(Fasciolidae), Gastrodiscoides
hominis (Gastrodiscidae), Watsonius watsoni, and Fischoederius elongatus (Paramphistomidae). Whereas F. hepatica and F. gigantica
are hepatic, the other four species are intestinal parasites.
Food-borne trematodiases are an emerging public health problem in Southeast Asia and Latin America and of growing importance for travel clinics in Europe and North America. The disease is caused by chronic infections with liver, lung, and intestinal flukes. This article focuses on the most important liver and lung flukes that parasitize man, namely Clonorchis sinensis, Fasciola gigantica, Fasciola hepatica, Opisthorchis felineus, Opisthorchis viverrini, and Paragonimus spp. The article describes the epidemiology of major liver and lung fluke infections, including current distribution, burden, life cycle, clinical signs and symptoms, diagnostic approaches, and current tools for prevention, treatment, and control.