Fish-borne Zoonotic Trematodes Prevalence Research Articles

Prevalence of fish-borne zoonotic trematode infection in Jilin Province, China.

Fish-borne zoonotic trematodes (FZTs) are the most serious food-borne parasites in Asia and have become a burden to public health and a new challenge in food safety. In Jilin Province, China, the prevalence of FZTs in intermediate and definitive hosts has not been extensively explored. In the present study, we investigated the prevalence of FZTs in Jilin Province, China. From July to November 2020, a total of 132 freshwater snails (the first intermediate host of FZTs), 4122 wild freshwater fishes (the second intermediate host of FZTs) and 143 fecal samples from canines, ducks and swine (the definitive host of FZTs) were collected from the Yitong River basin of Jilin Province. FZT species were identified by morphological observation combined with internal transcribed spacer (ITS) sequence analysis. The prevalence of FZTs was then calculated. The results showed that the prevailing species of FZTs in Jilin Province, China, were Clonorchis sinensis, Metorchis orientalis and Echinochasmus japonicus. The total prevalence of FZTs was 29.74% (1226/4122) in fish, the total infection rates were 2.27% (3/132) in snails, 75.00% (21/28) in canines and 37.18% (29/78) in ducks. The coinfection rates of the two trematodes were 13.39% (552/4122) in fish, 35.71% (10/28) in canines and 7.69% (6/78) in ducks. The coinfection rate of the three flukes was 2.60% (107/4122) in fish. Nine of the 12 fish species examined were infected with FZT metacercariae.

Seasonal prevalence of zoonotic trematode parasites in commercial catfish species in the Ho Chi Minh City area

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.

Prevalence of trematode in wild fish from fishing in Ho Chi Minh City

A research on the prevalence of fishborne zoonotic trematodes (FZT), metacercariae stage, in wild fish from fishing in Nhieu Loc – Thi Nghe, Tau Hu – Ben Nghe and Thay Cai – An Ha canals was conducted in Ho Chi Minh City in the period of May 2017 and April 2018. The results showed that no metacercariae were found in fish in Nhieu Loc – Thi Nghe and Tau Hu – Ben Nghe canals. However, wild fish in Thay Cai – An Ha canal were infected with Haplorchis pumilio and Centrocestus formosanus. Metacecariae were infected in silver barb (80%), climbing perch (11.7%), snakehead (7.5%), and walking catfish (1.7%). The FZT prevalence in the wet season is significantly higher than in the dry season (P

The effectiveness of different intervention strategies for the prevention of zoonotic metacercariae infection in cultured fish

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.

A Cross-Sectional Study on the Potential Transmission of the Carcinogenic Liver Fluke Opisthorchis viverrini and Other Fishborne Zoonotic Trematodes by Aquaculture Fish

Throughout Southeast Asia and China, eating raw and or partially cooked cyprinid fish causes liver (hepatobiliary) disease and cancer (cholangiocarcinoma) due to fishborne zoonotic trematodes (FZT), in particular Clonorchis sinensis and Opisthorchis viverrini. The primary source of transmission is by native fish, but aquaculture fish are also reported to have high infective potential. Here, a cross-sectional survey of FZT in fish farms was conducted in an endemic area in Khon Kaen Province, Thailand. By using conventional and polymerase chain reaction (PCR) methods, we detected O. viverrini and FZT metacercariae (Centrocestus formosanus and Haplorchis taichui) in two popular fish species, Barbonymus gonionotus (silver barb) and Cirrhinus mrigala (mrigal), from aquaculture farms. Both species were infected in five of six farms examined by PCR but not by conventional methods, yet the prevalence of FZT metacercariae in aquaculture fish was high (46.9%). In addition to O. viverrini (17.1%), the native fish Cyclocheilichthys armatus and Hampala dispar had a prevalence of FZT of 81.4%, which included 5.7% for C. formosanus and 17.1% for H. taichui by conventional method. To our knowledge, this is the first discovery of O. viverrini in aquaculture fish in Thailand. More comprehensive studies are required to determine if human-induced disease transmission coupled with natural transmission cycle occurs throughout the aquaculture industry in the region. This has significant impact on food quality and safety, and provides the basis for the development of an effective strategy for the prevention and control of foodborne diseases.

Relationship between snail population density and infection status of snails and fish with zoonotic trematodes in Vietnamese carp nurseries.

BackgroundFish-borne zoonotic trematodes (FZT) are a food safety and health concern in Vietnam. Humans and other final hosts acquire these parasites from eating raw or under-cooked fish with FZT metacercariae. Fish raised in ponds are exposed to cercariae shed by snail hosts that are common in fish farm ponds. Previous risk assessment on FZT transmission in the Red River Delta of Vietnam identified carp nursery ponds as major sites of transmission. In this study, we analyzed the association between snail population density and heterophyid trematode infection in snails with the rate of FZT transmission to juvenile fish raised in carp nurseries.Methodology/Principal FindingsSnail population density and prevalence of trematode (Heterophyidae) infections were determined in 48 carp nurseries producing Rohu juveniles, (Labeo rohita) in the Red River Delta area. Fish samples were examined at 3, 6 and 9 weeks after the juvenile fish were introduced into the ponds. There was a significant positive correlation between prevalence of FZT metacercariae in juvenile fish and density of infected snails. Thus, the odds of infection in juvenile fish were 4.36 and 11.32 times higher for ponds with medium and high density of snails, respectively, compared to ponds where no infected snails were found. Further, the intensity of fish FZT infections increased with the density of infected snails. Interestingly, however, some ponds with no or few infected snails were collected also had high prevalence and intensity of FZT in juvenile fish. This may be due to immigration of cercariae into the pond from external water sources.Conclusions/SignificanceThe total number and density of potential host snails and density of host snails infected with heterophyid trematodes in the aquaculture pond is a useful predictor for infections in juvenile fish, although infection levels in juvenile fish can occur despite low density or absence infected snails. This suggests that intervention programs to control FZT infection of fish should include not only intra-pond snail control, but also include water sources of allochthonous cercariae, i.e. canals supplying water to ponds as well as snail habitats outside the pond such as rice fields and surrounding ponds.

Distribution of trematodes in snails in ponds at integrated small-scale aquaculture farms

In integrated small-scale aquaculture farming, animal and human excreta maybe used as fish feed and pond fertilizer, thereby enhancing transmission of fish-borne zoonotic trematodes (FZTs) from final hosts, like humans, pigs and chickens, to snails. Areas within a pond could vary in trematode egg-load due to the immediate bordering land, and this might provide implications for control of these trematodes or sampling in field studies measuring FZT prevalence in snails. We therefore estimated the effect of bordering land use on prevalence and FZT burden in snails in different areas within small-scale aquaculture ponds. Nine sampling areas within a pond were assigned in six ponds. For each sampling area, about 120 Melanoides tuberculata snails were collected. Based on land use bordering a sampling area, these were categorized in 5 risk-categories: low-risk (road, rice planted in pond, agriculture, or middle of pond), human access point to pond, livestock sty (pigs or poultry), both human access point and livestock sty, and water connection to canal. In total, 5392 snails were collected. Percentages of snails with parapleurolophocercous cercariae varied between 6% in areas categorized as low-risk and areas with livestock sty only to 15% in areas with both human access point and livestock sty; only this 15% was significantly different from the prevalence in the low-risk category. Percentages of snails with xiphidio cercariae did not differ between risk-categories and varied between 5% and 10%. Mean snail size was 15.2mm, and was significantly associated with both the probability of infection as well as parasite burden. Very small differences in parasite burden were found at different land use areas; the maximum difference was about 11 cercariae. This study demonstrated only small differences between areas surrounding a pond on risk of snails to be infected with fish-borne trematodes within different pond areas. In field studies on FZTs in M. tuberculata snails in ponds, sampling from ponds can therefore be done without considering areas within ponds.

Freshwater Aquaculture Nurseries and Infection of Fish with Zoonotic Trematodes, Vietnam

Residents of the Red River Delta region of northern Vietnam have a long tradition of eating raw fish. Fish-borne zoonotic trematodes (FZTs) are estimated to infect ≈1 million persons in Vietnam. It remains uncertain at what stages in the aquaculture production cycle fish become infected with FZTs. Newly hatched fish (fry) from 8 hatcheries and juveniles from 27 nurseries were therefore examined for FZT infection. No FZTs were found in fry from hatcheries. In nurseries, FZT prevalence in juveniles was 14.1%, 48.6%, and 57.8% after 1 week, 4 weeks, and when overwintered in ponds, respectively. FZT prevalence was higher in grass carp (p<0.001) than in other carp species. Results show that nurseries are hot spots for FZT infections in fish. Thus, sustainable FZT prevention strategies must address aquaculture management practices, particularly in nurseries, to minimize the risk of distributing infected juveniles to grow-out ponds and, subsequently, to markets for human consumption.

Fish-Borne Zoonotic Trematodes in Cultured and Wild-Caught Freshwater Fish from the Red River Delta, Vietnam

Nam Dinh province in Red River Delta, Vietnam, is an endemic area for the human liver fluke Clonorchis sinensis, but little is known about its occurrence in the fish intermediate host in this region. A cross-sectional study was carried out to identify fish-borne zoonotic trematodes (FZT) species diversity and to estimate the prevalence and infection densities of FZT in three major types of fish: cultured species and self-recruiting species from family ponds and wild-caught species from irrigation canals in Nam Dinh province. A total of 714 wild-caught fish from canals and 829 fish from family ponds were examined for FZT infection. Only a single fish from a pond was infected with Cl. sinensis. The intestinal fluke Haplorchis pumilio was very common and found in more than 50% of fish irrespective of origin. Four other intestinal FZT species were found at low prevalence (<4.0%) except Procerovum varium, which was found in 14.4% of wild-caught fish. There was no significant difference (p > 0.05) in FZT prevalence in cultured fish (64.3%) compared with wild-caught fish (68.9%), nor between cultured fish species (65.1%) and self-recruiting species obtained from ponds (58.1%). The prevalence of FZT in silver carp (Hypophthalmichthys molitrix) (82.7%), grass carp (Ctenopharyngodon idellus) (76.9%), and mrigal (Cirrhinus mrigala) (63.8%) was significantly higher than that in rohu (Labeo rohita) (49.1%) (p < 0.001). The density of FZT metacercariae in fish from canals (0.56 metacercariae/g) was significantly higher (p < 0.001) than that in fish from ponds (0.03 metacercariae/g). The frequent occurrence of intestinal flukes in all fish types indicates that wild-caught and cultured fish are equally at risk of infection with FZT, particularly in species commonly used in Nam Dinh to prepare raw fish dishes. These results underscore the need for greater awareness of the risk from raw fish dishes among public health agencies and consumers.

Prevalence and risks for fishborne zoonotic trematode infections in domestic animals in a highly endemic area of North Vietnam

Fishborne zoonotic trematodes (FZT) are endemic in humans and cultured fish in Vietnam but little is known about FZT in domestic animals. A study was designed to determine FZT prevalence and species diversity, and risk factors for infection, in dogs, cats and pigs. Faecal samples from 186 dogs, 94 cats and 168 pigs belonging to 132 households in Nghia Hung district, Nam Dinh province, were examined for small trematode eggs; those were trematode eggs with length less than 50 μm. Prevalence of FZT varied significantly between cats (70.2%), dogs (56.9%) and pigs (7.7%). Forty-nine of the egg-positive animals (25 dogs, 20 cats and 4 pigs) were necropsied to obtain adult trematodes for identification. The liver fluke, Clonorchis sinensis, and 11 species of intestinal flukes including Haplorchis, Stellantchasmus, Stictodora and Centrocestus were recovered from the infected animals. The practice of feeding raw fish to the animals was a significant risk factor for infection; this risk was reduced if the animals were periodically treated with anthelmintics. Based on the high prevalence of FZT and certain risky husbandry practices, domestic animals are likely to be major contributors of FZT eggs to the environment. Therefore, education of farmers to avoid feeding raw fish and to perform regular anthelmintic treatment of dogs, cats and pigs is needed in integrated FZT control programs.

Prevalence of zoonotic trematode parasites in fish fry and juveniles in fish farms of the Mekong Delta, Vietnam

Zoonotic parasites are a significant food safety problem, particularly in Asia. In Vietnam fishborne zoonotic trematodes (FZT) are highly prevalent in fish cultured in grow-out farms. However, FZT infection status of juveniles produced and distributed by hatcheries and nurseries is unknown. Here we report an epidemiological investigation on FZT in fry and juveniles of major cultured freshwater fish species in four provinces of the Mekong Delta of Vietnam. No FZT infections were found in 14 species of fry sampled from hatcheries. In contrast, nursery juveniles of river catfish, hybrid catfish, giant gouramy, climbing perch, common carp, kissing gouramy, silver barb, silver carp, grass carp, Indian carp, pacu, tilapia and snakeskin gouramy were frequently infected with FZT metacercariae (range 1.2–29.7%). Seasonal variation in prevalence was observed: prevalence in river catfish and hybrid catfish were maximal in January, at the end of the flooding season, while the prevalence in juveniles of giant gouramy, climbing perch, common carp, kissing gouramy, silver barb, silver carp grass carp, mrigal and pacu were higher in the wet season, June to November. Overall, FZT prevalence was highest in climbing perch and giant gouramy (29.7% and 27.8%, respectively) and the lowest in river catfish (1.2%). The density of FZT metacercariae in fish varied seasonally only in climbing perch which was maximal in the wet season (P<0.05), compared to the dry season (430 vs 28 metacercariae/100 g of fish). These results demonstrate that acquisition of infected seed stock from nurseries is a serious risk for Vietnamese grow-out fish farms, and stress that interventions to control FZT must focus also on these stages of the cultured fish production cycle.

Animal Reservoir Hosts and Fish-borne Zoonotic Trematode Infections on Fish Farms, Vietnam

Fish-borne zoonotic trematodes (FZT) pose a risk to human food safety and health and may cause substantial economic losses in the aquaculture industry. In Nghe An Province, Vietnam, low prevalence of FZT for fish farmers but high prevalence for fish indicate that reservoir hosts other than humans may play a role in sustaining transmission. To determine whether domestic animals may be reservoir hosts, we assessed prevalence and species composition of FZT infections in dogs, cats, and pigs in a fish-farming community in Vietnam. Feces from 35 cats, 80 dogs, and 114 pigs contained small trematode eggs at 48.6%, 35.0%, and 14.4%, respectively; 7 species of adult FZT were recovered from these hosts. These results, combined with data from previous investigations in this community, imply that domestic animals serve as reservoir hosts for FZT and therefore must be included in any control programs to prevent FZT infection in humans.

Prevalence of fishborne zoonotic parasites in important cultured fish species in the Mekong Delta, Vietnam

A seasonal investigation on the occurrence of fishborne zoonotic trematodes (FZT) in economically important mono-cultured hybrid catfish and giant gouramy was conducted in the Mekong Delta of Vietnam. Fish from carp poly-culture and intensive small-scale integrated vegetable-aquaculture-animal husbandry farming (VAC) systems were also examined. No FZT metacercariae were found in any mono-cultured hybrid catfish. FZT metacercariae were common, however, in fish from the other three systems: All metacercariae belonged to the Heterophyidae family of trematodes, Haplorchis pumilio, H. taichui, Centrocestus formosanus and Stellantchasmus falcatus. The FZT prevalence was 1.7% in mono-cultured giant gouramy, 6.6% in carp from the poly-culture and 3.0% in fish raised in the VAC system. H. pumilio was the most common FZT species constituting more than 58.0% of all metacercariae recovered. The prevalence of infection was significantly higher in the flooding season compared to the non-flooding season for both giant gouramy and fish reared in the VAC system. FZT intensity was greatest in fish from carp poly-culture, particularly in the flooding season. The results indicate that certain fish production systems are at risk for FZT, and control approaches will benefit from understanding these risk factors.