An epidemiological study of fishborne zoonotic trematodes (FZT) infecting three major catfish species, hybrid catfish (Clarias sp.), river catfish (Pangasianodon hypopththalmus) and black-spotted catfish (Pangasius larnaudii), produced locally in Ho Chi Minh City, Vietnam, was conducted during 2017-2018. The impact of seasonal changes associated with the wet and dry seasons was assessed. The only species of FZT found was Haplorchis pumilio, a new host record for black-spotted catfish. Farm prevalence of H. pumilio was highest for black-spotted catfish (20.0 %) and hybrid catfish (16.7 %), and lowest for farms producing river catfish (5.0 %). The FZT prevalence in hybrid catfish (N = 300 per season) was higher in the wet season (2.0 %) than in the dry season (0.3 %); however, it was not significantly different (P > 0.05). For all three catfish species (N = 550 per season), seasonal prevalence was significantly higher (P < 0.05) in the wet season than in the dry season (1.5 % versus 0.2 %). These results demonstrate that, overall, most aquaculture farmers in this area employed management practices that were effective in lowering the risk of parasite infection in grow-out catfish compared with prevalence data for catfish reported from the Mekong Delta. However, the basis for the seasonal effect is not clear. The increase in snail intermediate host populations and pond contamination with parasites eggs from surface run-off are risk factors, generally, but the significantly higher impact on hybrid catfish production requires further investigation.

Humans suffer from numerous parasitic foodborne zoonoses, many of which are caused by helminths (‘worms’). The parasites discussed in this chapter include some of those which are transmitted by ingestion of raw or improperly prepared foods, such as meat, fish, and plants. While many people in developed countries are commonly aware of meat-borne parasites such as Trichinella ( trichinosis or trichinellosis), they are less familiar with those transmitted by fish, invertebrates and plants. The parasites selected for this chapter were chosen because they represent these different food hazards. In the discussion of these parasites basic information on the biology and epidemiology of the parasitic zoonosis is presented, along with information on the major human pathogenic and clinical problems caused by the accidental infection with them. Diagnsotic challenges and treatments for these parasites are also descrbed, however, emphasis is placed on measures that should be taken by people to prevent exposure to them. The information presented in this chapter is an overview, therefore, for a more detailed understanding of these zoonoses the reader is encouraged to consult the sources listed in the Citation list.

The liver and intestinal fish-borne zoonotic trematodes (flukes) are important parasites of humans and animals and are estimated to infect more than 18 million people, especially in Asia.The diseases caused by fish-borne liver flukes, clonorchiasis, opisthorchiasis and methorchiasis, can be severe.Infection with high worm burdens has high impact on health status in endemic areas; a recent estimation of the effect of liver flukes on morbidity yielded DALY value of 275,370.Because fish are a major source of protein and an important export commodity in western Siberia and South East Asia these diseases are of both economic and public health concern.Clonorchis sinensis is endemic in southern China, Korea and northern Vietnam, whereas O. viverrini is endemic in the Lower Mekong Basin, including Thailand, Lao People's Democratic Republic), Cambodia and south and central Vietnam.Opisthorchis felineus has been documented in at least 12 countries of the European Union, Belarus, Ukraine, and in Western Siberia (Russia).Methorchis species are wide spread, and reported from North America, Eurasia, and East Asia; however, information on human infections is very limited.The infective stage for humans, as well for animals, is the larval metacercaria stage present in fish that matures to the adult stage in the hepatobiliary system of humans and other fish-eating mammals.A significant feature of the epidemiology of these parasites is their wide definitive host range, which includes not only domestic animals but also sylvatic mammals such as rodents and carnivores.The adult flukes can survive for up to ten years in the host, producing around 200 eggs per day.This results in considerable contamination of the environment.Water becomes contaminated with fluke eggs from indiscriminate deposition of infected human and animal excreta, which, if ingested by appropriate snail hosts, are the source of the infective metacercariae found in fish.While those fecal egg sources associated with household fish ponds can be addressed by sanitation approaches, the common infection of wild fish from the sylvatic cycle of liver flukes is not amenable to sanitation interventions.

Trichinellosis is a cosmopolitan foodborne disease that may result in severe health disorders and even death. Despite international awareness of the public health risk associated with trichinellosis, current data on its public health impact are still lacking. Therefore we assessed, for the first known time, the global burden of trichinellosis using the Disability-Adjusted Life Year metric. The global number of DisabilityAdjusted Life Years due to trichinellosis was estimated to be 76 per billion persons per year (95% credible interval: 38–129). The World Health Organization European Region was the main contributor to this global burden, followed by the WHO region of the Americas and the World Health Organization Western Pacific region. The global burden of trichinellosis is much lower than that of other foodborne parasitic diseases and is in sharp contrast to the high budget allocated to prevent the disease in many industrialised countries. To decrease the uncertainty around the current estimates, more knowledge is needed on the level of underreporting of clinical trichinellosis in different parts of the world. DOI: https://doi.org/10.1016/j.ijpara.2014.05.006 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-108995 Accepted Version Originally published at: Devleesschauwer, Brecht; Praet, Nicolas; Speybroeck, Niko; Torgerson, Paul R; Haagsma, Juanita A; De Smet, Kris; Murrell, K Darwin; Pozio, Edoardo; Dorny, Pierre (2015). The low global burden of trichinellosis: evidence and implications. International Journal for Parasitology, 45(2-3):95-99. DOI: https://doi.org/10.1016/j.ijpara.2014.05.006 International Journal for Parasitology Succinctus The global burden of trichinellosis Brecht Devleesschauwer, Nicolas Praet*, Niko Speybroeck, Paul Torgerson, Juanita A Haagsma, Darwin Murrell, Edoardo Pozio, Pierre Dorny a Department of Virology, Parasitology and Immunology, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium; b Institute of Health and Society (IRSS), Université catholique de Louvain, Clos Chapelle-aux-Champs 30, 1200 Brussels, Belgium; c Department of Biomedical Sciences, Institute of Tropical Medicine, Nationalestraat 155, 2000 Antwerp, Belgium; d Section of Epidemiology, Vetsuisse Faculty, University of Zürich, Winterthurerstrasse 270, 8057 Zürich, Switzerland; e Erasmus MC, Department of Public Health, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands; f Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbojlen 4, DK-1870 Frederksberg C, Denmark; g Department of Infectious, Parasitic, and Immunomediated Diseases, Istituto Superiore di Sanità, viale Regina Elena 299, 00161 Rome, Italy. * These authors contributed equally to this work ° Corresponding author: Brecht Devleesschauwer; Department of Virology, Parasitology and Immunology, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium; Tel.: +32 9 264 7328; E-mail: Brecht.Devleesschauwer@UGent.be

Humans suffer from numerous parasitic foodborne zoonoses, many of which are caused by helminths ('worms'). The parasites discussed in this article include some of those which are transmitted by ingestion of raw or improperly prepared foods, such as meat, fish, and plants. While many people in developed countries are commonly aware of meat-borne parasites such as Trichinella (trichinosis or trichinellosis), they are less familiar with those transmitted by fish, invertebrates, and plants. The parasites selected for this article were chosen because they represent these different food hazards. In the discussion of these parasites, basic information on the biology and epidemiology of the parasitic zoonosis is presented, along with information on the major human pathogenic and clinical problems caused by the accidental infection with them. Diagnostic challenges and treatments for these parasites are also described; however, emphasis is placed on measures that should be taken by people to prevent exposure to them. The information presented in this article is an overview, therefore, for a more detailed understanding of these zoonoses the reader is encouraged to consult the sources listed in the citation list.

Infection with fish-borne zoonotic trematodes (FZT) is an important public health problem in many parts of Southeast Asia. People become infected with FZT when eating raw or undercooked fish that contain the infective stage (metacercariae) of FZT. The parasites require specific freshwater snails as first intermediate host and a variety of fish species, both wild caught and cultured, as second intermediate host. Aquaculture production has grown almost exponentially in SE Asia and in order to produce fish free from FZT metacercariae, it is important to mitigate factors promoting transmission to fish. Here we report results from a cross-sectional study to look at the association between pond depth and infection with FZT in giant gourami nursery ponds. Density of intermediate host snails was positively associated with pond depth (count ratio associated with a 1m increase in pond depth was 10.4 (95% C.L.: 1.61–67.1, p<0.5)) and this may partly explain the higher prevalence and intensity of FZT infection in juvenile fish. High fry stocking density (>200frym−3) was associated with lower host snail density (count ratio=0.15) than low stocking density (<100frym3). Ponds stocked with 100–200frym−3 had snail counts 0.76 (95% C.L.: 0.33–1.75, p n.s.) of those in ponds stocked with fry density of <100frym−3. Since density of intermediate snail hosts was associated with FZT transmission to fish, effort should be taken to reduce snail density prior to stocking the fry, but focus should also be on habitats surrounding ponds as transmission may occur through cercariae produced outside ponds and carried into ponds with water pumped into ponds.

Fish-borne zoonotic trematode parasites (FZT) pose a food safety and public health problem in Vietnam. The transmission cycle is complex as domestic animals, especially dogs, cats, fish-eating birds and pigs together with humans serve as reservoir hosts and contribute to FZT egg contamination of aquaculture ponds and the environment. This intervention trial was conducted to determine the effectiveness of various on-farm interventions, including reduction in FZT egg contamination through treatment of infected people and domestic animals, reduction in snail density through mud removal from aquaculture ponds prior to fish stocking, and various other measures in reducing FZT infection in juvenile striped catfish (Pangasianodon hypophthalmus) and giant gourami (Osphronemus goramy). Interventions were implemented on 5 farms for each fish species during production cycles in 2009 and 2010 while 5 similar farms for each species served as control. For both fish species, both prevalence and intensity of infection did not differ significantly between intervention and non-intervention farms prior to the interventions. The interventions significantly reduced both prevalence and intensity of FZT infection in the juvenile fish compared to control ponds. For giant gourami, odds of infection in intervention ponds was 0.13 (95% CL: 0.09–0.20; p<0.001) of that in non-intervention ponds after the 2009 trial and 0.07 (0.03–0.14; p<0.001) after the 2010 trial. For striped catfish, these figures were 0.17 (0.08–0.35; p<0.001) after the 2009 trial while after the 2010 trial all ponds with interventions were free from infection. Metacercariae intensity (no. of metacercariae/fish) in giant gourami from intervention ponds was 0.16 (0.11–0.23; p<0.001) of that in fish from non-intervention ponds after the 2009 trial and 0.07 (0.04–0.15; p<0.001) after the 2010 trial; for striped catfish these figures were 0.18 (0.09–0.36; p<0.001) and 0.00 (confidence limits not estimated), respectively. The aquaculture farm pond intervention approaches taken in this trial have the potential to reduce or eliminate FZT infections in fish and may be implemented across the entire region if adjusted to local conditions and fish species.

There is little information available on parasites of zoonotic significance in Cambodia. In 2011, in an effort to obtain data on potentially zoonotic gastrointestinal parasites in domestic animals, 50 dogs and 30 pigs residing in 38 households located in Ang Svay Check village, Takeo province, Cambodia were examined for parasites from faecal samples. The samples were processed using the formalin-ethyl acetate concentration technique (FECT). Hookworms were the most common zoonotic parasite found in dogs (80.0%) followed by Echinostomes (18.0%). While, in pigs, Fasciolopsis buski was the most common zoonotic parasite (30.0%) followed by Ascaris suum (13.3%). This study provides baseline data on gastrointestinal parasites in dogs and pigs from Cambodia and underscores the importance of domestic animals as reservoir hosts for human parasites for Cambodian veterinary and public health agencies. Follow-up studies are required to further taxonomically characterize these dog and pig parasites and to determine their role in human parasites in this community.

Fishborne zoonotic trematodes (FZT) are an emerging problem and there is now a consensus that, in addition to wild-caught fish, fish produced in aquaculture present a major food safety risk, especially in Southeast Asia where aquaculture is important economically. Current control programs target communities at risk through mass drug administration. However, we argue that treatment alone will not reduce the risk from eating infected fish and that sustainable effective control must adopt an integrated FZT control approach based on education, infrastructure improvements, and management practices that target critical control points in the aquaculture production cycle identified from a thorough understanding of FZT and host biology and epidemiology. We present recommendations for an integrated parasite management (IPM) program for aquaculture farms.

To the Editor: Fishborne zoonotic trematodes are highly prevalent in many Asian communities (1,2). Although presence of the liver fluke Clonorchis sinensis is well documented in Vietnam (3), evidence of the presence of the more common liver fluke of Southeast Asia, Opisthorchis viverrini, is only circumstantial. Surveys of human fecal samples have frequently reported O. viverrini fluke eggs in humans in southern and central Vietnam (4); however, identifications based on fecal eggs are notoriously unreliable for differentiating species of liver and intestinal flukes (5). The few reports of surgical recovery of adult O. viverrini flukes from humans do not eliminate the possibility of infection having been acquired during travel in neighboring fluke-endemic countries. Metaceraria from fish in the Mekong Delta have been tentatively identified as Opisthorchis spp., but this identity has not been confirmed (6). Specific identification is necessary for an understanding of the liver fluke diversity in Vietnam, especially because O. lobatus flukes, a related species that infects ducks, have been reported from nearby Laos (7). To clarify the status of fishborne liver flukes in Vietnam, during 2011–2012, we conducted a survey for liver fluke metacercariae in fish from Phu Yen Province. We selected this province because the local populations have a strong preference for raw fish and because previous surveys of human fecal samples conducted there indicated high prevalence of fishborne parasites (4). We chose to investigate metacercariae in fish to avoid the uncertainty of identifications based on fecal eggs and because of the availability of recent molecular methods for species identification of Opisthorchis fluke metacercariae (7). Fish were collected from Tuy Hoa City and from the districts of Hoa Xuan Dong, Tuy An, and Song Hinh; these 3 districts are areas of large aquaculture production of freshwater fish. Fresh fish from ponds, rice fields, rivers, and swamps were purchased at local markets from April 2011 through March 2012. The fish sellers provided information about the source of the fish (e.g., type of water body). Fish were transported live with mechanical aeration to the Research Institute for Aquaculture No. 3 in Nha Trang, where they were examined for metacercariae by use of whole individual fish pepsin digestion (8). Recovered metacercariae were examined microscopically, and those identified morphologically as Opisthorchis spp. flukes (9) were isolated. A subset of these metacercariae were fixed in 70% alcohol and examined by PCR and sequence analysis of the CO1 gene (7) at the Department of Helminthology, Mahidol University, Bangkok. For the purpose of obtaining adult worms, 3 hamsters were inoculated with the Opisthorchis metacercariae (15, 30, or 45 metacercariae/hamster). The adult worms were recovered from the infected hamsters 25–30 days after infection and were fixed and stained for morphologic determination of species (10). A total of 4 fish species were infected with O. viverrini metacercariae (Technical Appendix Table 1). Metacercariae prevalence was highest (28.1%) among crucian carp (Carasius auratus). Specific identification was confirmed by morphologic appearance of adult worms recovered from hamsters (Figure) and PCR and sequence analysis of the partial metacercarial CO1 gene, amplified by CO1-OV-Hap-F&R primers (7). Infected fish originated predominantly from so-called wild water (i.e., swamps, rice fields, rivers). The prevalence of O. viverrini metacercariae in crucian carp varied seasonally (Technical Appendix Table 2). Figure Morphologic appearance of different stages of Opisthorchis viverrini flukes. A) Encysted metacercariae. Scale bar indicates 30 μ. B) Metacercariae released from cyst. Scale bar indicates 30 μ. C) Carmine-stained adult worm from experimentally ... Crucian carp are cultured in some countries but not in Vietnam. However, the high prevalence and mean intensity of O. viverrini metacercariae (28.3 metacercariae/fish) is of public health concern because wild species such as crucian carp are often eaten raw, marinated, or lightly cooked. In contrast, infected barb (Puntius brevis) and rasbora (Rasbora spp.) fish (Technical Appendix Table 1) are not eaten raw. However, barb fish are invasive in farm fish ponds and can persist as a self-recruiting species; the presence of barb is an indication that pond management is insufficient to prevent invasive species of fish. Furthermore, barb fish are often fed to farm cats, which are major reservoir hosts for fishborne liver and intestinal trematodes. Infections (prevalence 8.3%) in snakehead fish (Channa spp.) also represent a food safety risk, because snakehead fish are cultured in Vietnam and are sometimes eaten raw or inadequately cooked. In addition to O. viverrini flukes, metacercariae of the zoonotic intestinal flukes Centrocestus formosanus, Haplorchis taichui, and H. yokogawi were recovered from snakehead and barb fish (Technical Appendix Table 1), all of which are common throughout Southeast Asia (1). The results of this study demonstrate that the human liver fluke O. viverrini is endemic to Vietnam and that it is being naturally transmitted to fish species that are often consumed raw or inadequately cooked. For determination of the prevalence, distribution, and epidemiology of O. viverrini flukes in fish, humans, and reservoir hosts (e.g., cats and dogs), these results need to be extended, especially because aquaculture is a growing industry in Vietnam. Technical Appendix: Prevalence and intensity of Opisthorchis viverrini fluke metacercariae in fish collected in several districts of Phu Yen Province, Vietnam, and in crucian carp collected monthly in An My commune, Tuy An district, Vietnam. Click here to view.(22K, pdf)

Fasciolosis, a helminthic parasitic disease caused by liver fluke Fasciola spp. is considered an emerging and reemerging parasitic disease of global significance. In the MENA region, which includes more than 20 countries of the Middle East and North Africa, human fasciolosis is most important in Iran and Egypt with more than 30,000 cases reported. Human and animal fasciolosis has been reported from all countries of the region but to a lesser extent. Important factors in this region that affect the prevalence of infectious diseases such as fasciolosis are the political turmoil and government instability that impede proper public health management. In this chapter, the authors describe the status, basic biology, epidemiology and clinical disease of fasciolosis in the region.

To the Editor: Fishborne zoonotic trematodes are highly prevalent in many Asian communities (1,2). Although presence of the liver fluke Clonorchis sinensis is well documented in Vietnam (3), evidence of the presence of the more common liver fluke of Southeast Asia, Opisthorchis viverrini, is only circumstantial. Surveys of human fecal samples have frequently reported O. viverrini fluke eggs in humans in southern and central Vietnam (4); however, identifications based on fecal eggs are notoriously unreliable for differentiating species of liver and intestinal flukes (5). The few reports of surgical recovery of adult O. viverrini flukes from humans do not eliminate the possibility of infection having been acquired during travel in neighboring fluke-endemic countries. Metaceraria from fish in the Mekong Delta have been tentatively identified as Opisthorchis spp., but this identity has not been confirmed (6). Specific identification is necessary for an understanding of the liver fluke diversity in Vietnam, especially because O. lobatus flukes, a related species that infects ducks, have been reported from nearby Laos (7). To clarify the status of fishborne liver flukes in Vietnam, during 2011–2012, we conducted a survey for liver fluke metacercariae in fish from Phu Yen Province. We selected this province because the local populations have a strong preference for raw fish and because previous surveys of human fecal samples conducted there indicated high prevalence of fishborne parasites (4). We chose to investigate metacercariae in fish to avoid the uncertainty of identifications based on fecal eggs and because of the availability of recent molecular methods for species identification of Opisthorchis fluke metacercariae (7). Fish were collected from Tuy Hoa City and from the districts of Hoa Xuan Dong, Tuy An, and Song Hinh; these 3 districts are areas of large aquaculture production of freshwater fish. Fresh fish from ponds, rice fields, rivers, and swamps were purchased at local markets from April 2011 through March 2012. The fish sellers provided information about the source of the fish (e.g., type of water body). Fish were transported live with mechanical aeration to the Research Institute for Aquaculture No. 3 in Nha Trang, where they were examined for metacercariae by use of whole individual fish pepsin digestion (8). Recovered metacercariae were examined microscopically, and those identified morphologically as Opisthorchis spp. flukes (9) were isolated. A subset of these metacercariae were fixed in 70% alcohol and examined by PCR and sequence analysis of the CO1 gene (7) at the Department of Helminthology, Mahidol University, Bangkok. For the purpose of obtaining adult worms, 3 hamsters were inoculated with the Opisthorchis metacercariae (15, 30, or 45 metacercariae/hamster). The adult worms were recovered from the infected hamsters 25–30 days after infection and were fixed and stained for morphologic determination of species (10). A total of 4 fish species were infected with O. viverrini metacercariae (Technical Appendix Table 1). Metacercariae prevalence was highest (28.1%) among crucian carp (Carasius auratus). Specific identification was confirmed by morphologic appearance of adult worms recovered from hamsters (Figure) and PCR and sequence analysis of the partial metacercarial CO1 gene, amplified by CO1-OV-Hap-F&R primers (7). Infected fish originated predominantly from so-called wild water (i.e., swamps, rice fields, rivers). The prevalence of O. viverrini metacercariae in crucian carp varied seasonally (Technical Appendix Table 2). Figure Morphologic appearance of different stages of Opisthorchis viverrini flukes. A) Encysted metacercariae. Scale bar indicates 30 μ. B) Metacercariae released from cyst. Scale bar indicates 30 μ. C) Carmine-stained adult worm from experimentally ... Crucian carp are cultured in some countries but not in Vietnam. However, the high prevalence and mean intensity of O. viverrini metacercariae (28.3 metacercariae/fish) is of public health concern because wild species such as crucian carp are often eaten raw, marinated, or lightly cooked. In contrast, infected barb (Puntius brevis) and rasbora (Rasbora spp.) fish (Technical Appendix Table 1) are not eaten raw. However, barb fish are invasive in farm fish ponds and can persist as a self-recruiting species; the presence of barb is an indication that pond management is insufficient to prevent invasive species of fish. Furthermore, barb fish are often fed to farm cats, which are major reservoir hosts for fishborne liver and intestinal trematodes. Infections (prevalence 8.3%) in snakehead fish (Channa spp.) also represent a food safety risk, because snakehead fish are cultured in Vietnam and are sometimes eaten raw or inadequately cooked. In addition to O. viverrini flukes, metacercariae of the zoonotic intestinal flukes Centrocestus formosanus, Haplorchis taichui, and H. yokogawi were recovered from snakehead and barb fish (Technical Appendix Table 1), all of which are common throughout Southeast Asia (1). The results of this study demonstrate that the human liver fluke O. viverrini is endemic to Vietnam and that it is being naturally transmitted to fish species that are often consumed raw or inadequately cooked. For determination of the prevalence, distribution, and epidemiology of O. viverrini flukes in fish, humans, and reservoir hosts (e.g., cats and dogs), these results need to be extended, especially because aquaculture is a growing industry in Vietnam. Technical Appendix: Prevalence and intensity of Opisthorchis viverrini fluke metacercariae in fish collected in several districts of Phu Yen Province, Vietnam, and in crucian carp collected monthly in An My commune, Tuy An district, Vietnam. Click here to view.(22K, pdf)

fed to farm cats, which are major reservoir hosts for fishborne liver and intestinal trematodes. Infections (prevalence 8.3%) in snakehead fish (Channa spp.) also represent a food safety risk, because snakehead fish are cultured in Vietnam and are sometimes eaten raw or inadequately cooked. In addition to O. viverrini flukes, metacercariae of the zoonotic intestinal flukes Centrocestus formosanus, Haplorchis taichui, and H. yokogawi were recovered from snakehead and barb fish (online Technical Appendix Table 1), all of which are common throughout Southeast Asia (1). The results of this study demonstrate that the human liver fluke O. viverrini is endemic to Vietnam and that it is being naturally transmitted to fish species that are often consumed raw or inadequately cooked. For determination of the prevalence, distribution, and epidemiology of O. viverrini flukes in fish, humans, and reservoir hosts (e.g., cats and dogs), these results need to be extended, especially because aquaculture is a growing industry in Vietnam.

Trichinellosis is a cosmopolitan foodborne disease that may result in severe health disorders and even death. Despite international awareness of the public health risk associated with trichinellosis, current data on its public health impact are still lacking. Therefore we assessed, for the first known time, the global burden of trichinellosis using the Disability-Adjusted Life Year metric. The global number of Disability-Adjusted Life Years due to trichinellosis was estimated to be 76 per billion persons per year (95% credible interval: 38–129). The World Health Organization European Region was the main contributor to this global burden, followed by the WHO region of the Americas and the World Health Organization Western Pacific region. The global burden of trichinellosis is much lower than that of other foodborne parasitic diseases and is in sharp contrast to the high budget allocated to prevent the disease in many industrialised countries. To decrease the uncertainty around the current estimates, more knowledge is needed on the level of underreporting of clinical trichinellosis in different parts of the world.

Fish-borne zoonotic trematodes (FZT) are a major public health problem. It is estimated that in Vietnam 26,366 “disability-adjusted life years” (DALYs) are lost due to FZT. Fish from aquaculture are a main source of protein and of great economic importance in both rural and urban areas. The objective of this study was to compare the impact on transmission of FZT to juvenile fish of drug treatment intervention of final hosts, and pond management interventions on fingerlings produced in nurseries producing Rohu carp in Northern Vietnam. The study design was a parallel group design of nurseries with two intervention groups; a drug treatment of human and animal groups and a farm management group (control of snail vectors and fecal pollution of pond). A third group (non-intervention) served as control. Fish were examined for FZT metacercariae prevalence and intensity before and after interventions, along with density of potential host pond snails. Fecal exams for FZT infections in farm household humans, dogs and cats were also performed. The results showed that although FZT prevalence in fish was not significantly reduced, the intensity of metacercariae in fish from ponds receiving management interventions was reduced 91.7% compared to before interventions. The intensity of FZT was also significantly lower in the pond management group, compared to the drug treatment group and the control group after interventions. The results demonstrate that improving farm and pond management practices can be effective in reducing FZT infections without using drug treatment. This study also highlighted certain obstacles to attaining higher levels of protection for which more research is needed. A major challenge is the ability to completely isolate (or bio-secure) the pond from its surrounding environment, especially surrounding water sources which may harbor snails and cercariae that can contaminate the pond through water resupply or runoff. Another is the unknown risk from piscivorous birds, host for intestinal FZT. The strategies employed in this study now need long-term evaluation on a regional basis, the outcome of which could be the development of good management practices crucial to ensuring a good quality product that benefits farmers and the consumers.

Guangdong province is the most important region for tilapia culture in China. However, it is also an endemic region for fishborne zoonotic trematodes (FZT), which pose a risk to human food safety and health. A study was designed to assess the status of trematode parasite infections in tilapia aquaculture systems as an indicator of potential risks from FZT associated with consumption of tilapia. Tilapia from nursery and grow-out ponds were sampled from monoculture, polyculture and integrated aquaculture systems. The results from 388 tilapia examined revealed a very low prevalence (1.5%) of trematode infections (Heterophyidae and Echinostomatidae). Integrated systems using animal manure and latrine wastes as fertilizer did not show a higher prevalence of FZT. Because it was not clear whether the low risk of infection was attributable to existing effective pond management practices or a low risk of spillover of FZT from area sylvatic reservoir hosts, a survey of local wild-caught fish was conducted. Five species of FZT were discovered from a total of 271 wild-caught fish and a mean infection density of 4.0 metacercariae/100g; FZT discovered included intestinal flukes (Haplorchis spp., Procerovum varium, and Metagonimus spp.) and metacercariae tentatively identified as Clonorchis sinenesis. The common occurrence of FZT in wild-caught fish suggests that the presence of FZT in local wild animal reservoirs is substantial, and that although the current aquaculture management systems for tilapia are generally effective in preventing transmission of these parasites into tilapia production systems, the improvement of pond management practices and biosecurity must be maintained at a high level.

Consumption of raw freshwater fish produced in both rural farm and urban wastewater ponds is a common practice in Vietnam. The present study assessed the risk of fish-borne zoonotic trematode (FZT) infection from fish raised in both these aquaculture systems in northern Vietnam. The diversity, prevalence, and infection intensity of FZT metacercariae in 1,500 freshwater fish collected from 6 sites located in rural and urban areas in northern Vietnam were investigated. The specific diagnosis of species was made by morphologic methods. The overall FZT prevalence in fish from both urban wastewater ponds and rural farm ponds was 11.2%. In wastewater ponds, the overall prevalence was 5.1%, ranging from 2.0% in tilapia to 7.3% in common and grass carp. In fish from farm ponds, the prevalence was 17.3%, and ranged from 6.7% in mud carp to 26.7% in common carp. The mean intensity of FZT infection was also higher in fish from farm ponds than that in fish from wastewater ponds (6.0% and 8.4%, respectively). The FZT species recovered from infected fish included both liver (Clonorchis sinensis) and intestinal flukes (Haplorchis taichui, Haplorchis pumilio, and Centrocestus formosanus). The prevalence of FZT in fish raised in these common farm systems represents a significant public health risk for a population with a strong cultural preference for consuming raw or inadequately prepared fish. These research results should encourage the public health and agriculture sectors to conduct the risk factor research required to develop control programs for FZT.