Epidemiological study on Clonorchis sinensis infection in Shenzhen area of Zhujiang delta in China

Long-Term Trend Analysis of Major Human Helminth Infections - Guangdong Province, China, 1988-2021

INTRODUCTION

Although helminth infections threaten millions of people worldwide, the spatiotemporal characteristics remain unclear across China. This study systematically describes the spatiotemporal changes of major human helminth infections and their epidemiological characteristics from 1988 to 2021 in Guangdong Province, China.

METHODS

The survey data in Guangdong Province were primarily obtained from 3 national surveys implemented during 1988-1992, 2001-2004, and 2014-2016, respectively, and from the China Information System for Disease Control and Prevention during 2019-2021. A modified Kato-Katz technique was used to detect parasite eggs in collected fecal samples.

RESULTS

The overall standardized infection rates (SIRs) of any soil-transmitted helminths (STH) and Clonorchis sinensis decreased from 65.27% during 1988-1992 to 4.23% during 2019-2021. In particular, the SIRs of STH had even more of a decrease, from 64.41% during 1988-1992 to 0.31% during 2019-2021. The SIRs of Clonorchis sinensis in the 4 surveys were 2.40%, 12.17%, 5.20%, and 3.93%, respectively. This study observed different permutations of gender, age, occupation, and education level on the SIRs of helminths.

CONCLUSIONS

The infection rate of STH has substantially decreased. However, the infection rate of Clonorchis sinensis has had fewer changes, and it has become the dominant helminth.

Functional characterization of Clonorchis sinensis sodium-bile acid co-transporter (CsSBAT) as a steroid sulfate transporter

Clonorchis sinensis (Cs) is a common trematode in Asian countries. Infection by Cs can result in many clinical symptoms. Here, a cDNA encoding a Cs apical sodium-dependent bile acid transporter (CsSBAT) was isolated from a Cs cDNA library, and functional characterization was performed using Xenopus laevis oocyte expression system. When expressed in Xenopus laevis oocytes, CsSBAT mediated the transport of radiolabeled estrone sulfate and dehydroepiandrosterone sulfate. No trans-uptake of carnitine, estradiol 17 β-D glucuronide, prostaglandin E₂, p-aminohippuric acid, α-ketoglutaric acid, and tetraethylammonium was observed. CsSBAT-mediated estrone sulfate uptake was in a time- and sodium-dependent manner. CsSBAT showed no exchange properties in efflux experiments. Concentration-dependent results showed saturable kinetics consistent with the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 0.3 ± 0.04 μM for [³H]estrone sulfate. CsSBAT-mediated estrone sulfate uptake was strongly inhibited by sulfate conjugates but not glucuronide conjugates. These findings contribute to our understanding of CsSBAT transport properties and the cascade of estrogen metabolite movement in Cs.

Novel mechanism of hepatobiliary system damage and immunoglobulin G4 elevation caused by Clonorchis sinensis infection

Clonorchis sinensis infection is still a major public health problem. It is estimated that more than 15 million people worldwide are infected, especially in Northeast China, Taiwan, South Korea, and North Vietnam. The detection of Clonorchis sinensis eggs in feces and bile is still the only gold standard for the diagnosis of Clonorchis sinensis infection, and new detection methods are needed to improve the detection rate. After Clonorchis sinensis invades the human body, it mainly parasitizes the hepatobiliary tract. Therefore, it is closely related to hepatobiliary diseases such as cholangitis, bile duct stones, liver fibrosis, and cholangiocarcinoma. The increase in immunoglobulin G4 (IgG4) caused by Clonorchis sinensis infection is rare and there are few reports about the relevant mechanism. It may be related to the inflammatory factors interleukin (IL)-4, IL-10, and IL-13 produced by human phagocytes, T cells, B cells, and other immune cells in the process of resisting the invasion of Clonorchis sinensis. However, this finding still needs further clarification and confirmation. This article reviews the epidemiology, clinical manifestations, serology, imaging, pathogenic mechanism, and control measures of Clonorchis sinensis infection to help establish the diagnostic process for Clonorchis sinensis. We report novel mechanisms of IgG4 elevation due to Clonorchis sinensis infection to provide more experience and a theoretical basis for clinical diagnosis and treatment of this infection.

Are Melanoides tuberculata and Tarebia granifera (Gastropoda, Thiaridae), suitable first intermediate hosts of Clonorchis sinensis in Vietnam?

Background

Two thiarid snail species, Melanoides tuberculata and Tarebia granifera have been reported as first intermediate hosts of the liver fluke Clonorchis sinensis; however, their role as true first intermediate hosts has not been verified. Thus, the present study aimed to clarify the suitability of these two snail species as first intermediate hosts of C. sinensis. This was accomplished by collecting snails from a highly endemic area for C. sinensis in Vietnam, the Thac Ba reservoir, and identifying shed cercariae using molecular techniques. We also conducted experimental infections of five snail species including M. tuberculata and T. granifera with eggs of C. sinensis.

Methodology/Principal findings

A total of 11,985 snails, representing 10 species were sampled. Five snail species, M. tuberculata, T. granifera, Lymnaea swinhoei, Parafossarulus manchouricus, and Bithynia fuchsiana were found shedding cercariae with an overall prevalence of infection ranging from 0.7% to 11.5%. Seven cercarial types were recorded. Cercariae of C. sinensis were only found in Parafossarulus manchouricus. Using a multiplex PCR approach for detecting C. sinensis infection, the prevalence in P. manchouricus was 4.2%. Additionally, all five snail species were experimentally exposed to C. sinensis eggs, however only P. manchouricus was successfully infected with an infection rate of 7.87%.

Conclusions/Significance

We confirmed that in the Thac Ba reservoir, Vietnam, the two thiarids, M. tuberculata and T. granifera are not suitable first intermediate hosts of C. sinensis. Only P. manchouricus was found infected by C. sinensis in nature, and was the only species that became infected experimentally.

Currently 13 snail species are reported as first intermediate hosts of Clonorchis sinensis, including two species of the Thiaridae, Melanoides tuberculata and Tarebia granifera. Both snail species have wide distributions in tropical and subtropical waters across the World, while the distribution of C. sinensis is much narrower and only occurs in endemic areas of East Asia. The role that these two thiarid snail species plays as successful hosts of C. sinensis, however, has been refuted in other studies. The present study was conducted to clarify this issue. Based on the results from field surveys in a newly discovered and highly endemic area for C. sinensis, as well as, data obtained under experimental conditions, we confirm that in Northern Vietnam, the two thiarid snail species are not successful first intermediate host of C. sinensis. C. sinensis was only detected in a single snail species, Parafossarulus manchouricus, through observation, molecular analyses and experimental infections.

Zoonotic parasites carried by invasive alien species in China

BACKGROUND

The invasive alien species may lead to great environmental and economic crisis due to its strong capability of occupying the biological niche of native species and altering the ecosystem of the invaded area. However, its potential to serve as the vectors of some specific zoonotic pathogens, especially parasites, has been neglected. Thus, the damage that it may cause has been hugely underestimated in this aspect, which is actually an important public health problem. This paper aims to discuss the current status of zoonotic parasites carried by invasive alien species in China.

MAIN BODY

This review summarizes the reported zoonotic parasites carried by invasive alien species in China based on the Database of Invasive Alien Species in China. We summarize their prevalence, threat to human health, related reported cases, and the roles of invasive alien species in the life cycle of these parasites, and the invasion history of some invasive alien species. Furthermore, we sum up the current state of prevention and control of invasive alien species in China, and discuss about the urgency and several feasible strategies for the prevention and control of these zoonoses under the background of booming international communications and inevitable globalization.

CONCLUSIONS

Information of the zoonotic parasites carried by invasive alien species neither in China or worldwide, especially related case reports, is limited due to a long-time neglection and lack of monitoring. The underestimation of their damage requires more attention to the monitoring and control and compulsory measures should be taken to control the invasive alien species carrying zoonotic parasites.

Mothers' Opisthorchis viverrini infection status and raw fish dish consumption in Lao People's Democratic Republic: determinants of child infection status

Background

Opisthorchis viverrini (Ov) infection is one of the foodborne trematodiases, which is highly endemic in Lao People’s Democratic Republic (PDR). The infection occurs especially when people eat raw fish containing Ov metacercariae. As eating raw fish is a traditional culture in Lao PDR, changing this behavior is difficult. A new approach is necessary to control Ov infection because people easily get re-infected even after taking praziquantel unless they change their behaviors. This study aimed to explore factors associated with Ov infection among children and to identify the existing behaviors and perception that might contribute to the control of Ov infection in Lao PDR. We conducted a cross-sectional study in Yommalath district, Khammouane province, in Lao PDR in August and September 2015. In this cross-sectional study, we used a semi-structured questionnaire and interviewed 348 mothers who had a child aged 5–15 years. We also collected the fecal samples from each mother-child pair and used the Kato-Katz method (three slides/sample) to detect Ov eggs.

Results

Of 284 children, 82.8% were infected with Ov. The children were more likely to be infected with Ov when their mothers were infected with Ov (adjusted odds ratio [AOR] 10.45, 95% confidence interval [CI] 3.13–34.86) or when their mothers liked raw fish dishes (AOR 2.47, 95% CI 1.07–5.69). Even though most mothers are primarily in charge of cooking family meals, fathers were also involved in the preparation of raw fish dishes.

Conclusion

This study suggests that a new approach to control Ov infection should target families or communities, rather than children only. Cooking or food preparation behaviors should be investigated in more depth.

Clonorchis sinensis and Clonorchiasis: The Relevance of Exploring Genetic Variation

Parasitic trematodes (flukes) cause substantial mortality and morbidity in humans. The Chinese liver fluke, Clonorchis sinensis, is one of the most destructive parasitic worms in humans in China, Vietnam, Korea and the Russian Far East. Although C. sinensis infection can be controlled relatively well using anthelmintics, the worm is carcinogenic, inducing cholangiocarcinoma and causing major suffering in ~15 million people in Asia. This chapter provides an account of C. sinensis and clonorchiasis research-covering aspects of biology, epidemiology, pathogenesis and immunity, diagnosis, treatment and control, genetics and genomics. It also describes progress in the area of molecular biology (genetics, genomics, transcriptomics and proteomics) and highlights challenges associated with comparative genomics and population genetics. It then reviews recent advances in the sequencing and characterisation of the mitochondrial and nuclear genomes for a Korean isolate of C. sinensis and summarises salient comparative genomic work and the implications thereof. The chapter concludes by considering how advances in genomic and informatics will enable research on the genetics of C. sinensis and related parasites, as well as the discovery of new fluke-specific intervention targets.

An Integrated Control Strategy Takes Clonorchis sinensis Under Control in an Endemic Area in South China

Clonorchis sinensis is an important foodborne zoonosis worldwide and prevalent in China for more than 2000 years. According to the experience of controlling Schistosoma japonica, China started to establish the integrated control strategy for C. sinensis in endemic areas. Lou village, the largest village in Shenzhen city in South China was taken as a pilot site. This longitudinal study assessed the infection status of C. sinensis among people and intermediate hosts from 2006 to 2014 in Lou village. After a continuous intervention with the integrated control strategy, the prevalence of C. sinensis decreased significantly to 2.01% in 2014. The infection intensity also reduced significantly with eggs per gram varying from 45.6 ± 3.4 in 2010 to 21.7 ± 1.6 in 2012. There is also a statistically significant decrease of the prevalence of C. sinensis metacercariae in fish hosts from 16.51% in 2008 before the intervention to 5.33% in 2014. All the old-styled toilets were replaced by sanitary ones with a harmless processing design in 2014. No viable parasite eggs were detected in stool samples from the reconstructed toilets. Health education played an important role in changing the eating habits among the local residents, with a significant decrease in the prevalence of eating raw fish from 91.99% in 2008 to 59.87% in 2014. The evaluation suggested that the integrated strategy we have performed in Lou village is effective in controlling the C. sinensis infection and maintaining the infection rate at a lower level, which can be promoted in other endemic areas.

Epidemiological and Clinical Parameters Features of Patients with Clonorchiasis in the Geum River Basin, Republic of Korea

This study was conducted to evaluate the infection rates of Clonorchis sinensis and laboratory findings in infected people. The 3,167 fecal samples, from nine villages in Okcheon-gun, were examined.

Risk factors for Clonorchis sinensis infection transmission in humans in northern Vietnam: A descriptive and social network analysis study

Clonorchis sinensis is major fish-borne trematode, endemic in North Vietnam. Risk factors described so far include individual eating behaviors and environmental factors. Here, additional to conventional risk factors, we report on socially influenced liver fluke transmission in endemic communities. A cross-sectional study on risk factors and fish sharing networks was conducted in 4 villages of Gia Thinh Commune, Ninh Binh Province. A total of 510 residents in 272 households were recruited for risk factor analysis while 220 households, 28 fishermen and 10 fish-sellers were enrolled for social network study. Fecal examination for C. sinensis eggs was performed. Average C. sinensis infection rate at Gia Thinh commune was 16.5% (range 2% to 34.4%). Higher infection rates were significantly associated with males, lower educational levels, eating raw fish, and location of the villages. Social network analysis (SNA) showed a strong positive correlation between ego network size (number of households in fish sharing network) and quantity of raw fish consumed (r=0.603, P<0.05). The infection rate in people who ate raw-fish caught from a nearby river was significantly higher than those who consumed fish taken from farmed ponds (P<0.05). The amount of raw-fish meal consumed per resident/year was significantly higher in villages that had a strong network of sharing raw-fish food (P<0.001). This study reports for the first time on fish-food sharing among neighbors, proximity to water bodies, frequency of eating raw fish from natural water bodies and low education were key risk factors in C. sinensis infection transmission in northern Vietnam.

Clonorchiasis

On Aug 21, 1875, James McConnell published in The Lancet his findings from a post-mortem examination of a 20-year-old Chinese man--undertaken at the Medical College Hospital in Calcutta, India--in whom he found Clonorchis sinensis in the bile ducts. Now, exactly 140 years later, we have a sound understanding of the lifecycle of this liver fluke, including key clinical, diagnostic, and epidemiological features. Developments in the so-called -omics sciences have not only advanced our knowledge of the biology and pathology of the parasite, but also led to the discovery of new diagnostic, drug, and vaccine targets. C sinensis infection is primarily related to liver and biliary disorders, especially cholangiocarcinoma. Clonorchiasis mainly occurs in east Asia, as a result of the region's social-ecological systems and deeply rooted cultural habit of consuming raw freshwater fish. The Kato-Katz technique, applied on fresh stool samples, is the most widely used diagnostic approach. Praziquantel is the treatment of choice and has been considered for preventive chemotherapy. Tribendimidine showed good safety and therapeutic profiles in phase 2 trials and warrants further investigation. Still today, the precise distribution, the exact number of infected people, subtle morbidities and pathogenesis, and the global burden of clonorchiasis are unknown. Integrated control strategies, consisting of preventive chemotherapy; information, education, and communication; environmental management; and capacity building through intersectoral collaboration should be advocated.

Molecular cloning and functional characterization of a glucose transporter (CsGLUT) in Clonorchis sinensis

A complementary DNA (cDNA) encoding a glucose transporter of Clonorchis sinensis (CsGLUT) was isolated from the adult C. sinensis cDNA library. The open reading frame of CsGLUT cDNA consists of 1653 base pairs that encode a 550-amino acid residue protein. Hydropathy analysis suggested that CsGLUT possess 12 putative membrane-spanning domains. The Northern blot analysis result using poly(A)(+)RNA showed a strong band at ~2.1 kb for CsGLUT. When expressed in Xenopus oocytes, CsGLUT mediated the transport of radiolabeled deoxy-D-glucose in a time-dependent but sodium-independent manner. Concentration-dependency results showed saturable kinetics and followed the Michaelis-Menten equation. Nonlinear regression analyses yielded a Km value of 588.5 ± 53.0 μM and a Vmax value of 1500.0 ± 67.5 pmol/oocyte/30 min for [1,2-(3)H]2-deoxy-D-glucose. No trans-uptakes of bile acid (taurocholic acid), amino acids (tryptophan and arginine), or p-aminohippuric acid were observed. CsGLUT-mediated transport of deoxyglucose was significantly and concentration-dependently inhibited by radio-unlabeled deoxyglucose and D-glucose. 3-O-Methylglucose at 10 and 100 μM inhibited deoxyglucose uptake by ~50 % without concentration dependence. No inhibitory effects by galactose, mannose, and fructose were observed. This work may contribute to the molecular biological study of carbohydrate metabolism and new drug development of C. sinensis.

Prevalence and risk factors of clonorchiasis among residents of riverside areas in Muju-gun, Jeollabuk-do, Korea

We evaluated the status of Clonorchis sinensis infection and potential risk factors among residents of riverside areas (Geumgang) in Muju-gun, Jeollabuk-do (Province), Korea. From January to February 2010, a total of 349 (171 males, 178 females) stool samples were collected and examined by the formalin-ether concentration technique. Also, village residents were interviewed using questionnaires to obtain information about C. sinensis infection-related risk factors. Overall egg-positive rate of C. sinensis was 13.2%. Egg-positive rates were significantly higher in males, farmers, and residents who had lived there more than 20 years, and in residents who had eaten raw freshwater fish than in opposite groups, respectively. However, there was no significant difference between age groups, education levels, cigarette smoking, alcohol drinking, health status, past history of infection, and experience of clonorchiasis medication and examination. Logistic regression analysis was performed to determine risk factors for clonorchiasis. On univariate analysis, the odds ratios for males, farmers, those who had lived there more than 20 years, and who had eaten raw freshwater fish were 2.41, 4.44, 3.16, and 4.88 times higher than those of the opposites, respectively. On multivariate analysis, the odds ratio of residents who had eaten raw freshwater fish was 3.2-fold higher than that of those who had not. These results indicate that residents living in Muju-gun, along the Geum River, Korea, have relatively high C. sinensis egg-positive rates, and the habit of eating raw freshwater fish was the major factor for the maintenance of clonorchiasis.

Prevalence and Risk Factors of Clonorchiasis among the Populations Served by Primary Healthcare Posts along Five Major Rivers in South Korea

Objectives:

Clonorchiasis is an infectious disease caused by the Chinese liver fluke Clonorchis sinensis. In this study, we investigated the prevalence and risk factors of clonorchiasis among the populations served by primary healthcare posts along five major rivers in South Korea.

Methods:

Forty primary healthcare posts that are located less than 5 km from one of the five rivers were selected from 26 counties. For the purpose of the survey, community health practitioners selected the nearest villages from the riversides in their own catchment area. From January to May 2009, a total of 2788 stool samples were collected and examined using the formalin–ether sedimentation technique. Village inhabitants were also interviewed by means of questionnaires in order to obtain information on potential risk factors.

Results:

The prevalence rates of clonorchiasis at various river basins were as follows: Seomjin River, 21.3%; Nakdong River, 13.5%; Geum River, 9.2%; Han River, 7.6%; and Yeongsan River, 4.9%. The total number of people infected with C. sinensis was 329 (11.3%). By gender, 14.3% of males and 7.6% of females were infected. In case of both males and females, the prevalence rate was highest in those in their 40s. Consumption of raw freshwater fish was confirmed as a risk factor based on a logistic regression analysis.

Conclusion:

The present findings suggest that clonorchiasis is still highly prevalent among the inhabitants of riverside areas in southern Korea, and, accordingly, it is necessary to implement a systematic control program in the endemic areas.

The identification of antigenic proteins: 14-3-3 protein and propionyl-CoA carboxylase in Clonorchis sinensis

Clonorchis sinensis, the causative agent of clonorchiasis, is widespread in East and Southeast Asia, including China, Vietnam and the Republic of Korea. We identified antigenic proteins from adult C. sinensis liver flukes using immunoproteomic analysis. In this study, we found 23 candidate antigenic proteins with a pI in the range of 5.4-6.2 in total lysates of C. sinensis. The antigenic protein spots reacted against sera from clonorchiasis patients and were identified as cysteine proteases, glutathione transferases, gelsolin, propionyl-CoA carboxylase (PCC), prohibitin and 14-3-3 protein (14-3-3) using LC-coupled ESI-MS/MS and an EST database for C. sinensis. PCC and 14-3-3 were identified for the first time as serological antigens for the diagnosis of C. sinensis. To validate the antigenicity of PCC and 14-3-3, recombinant proteins were immunoblotted with sera from clonorchiasis patients. The structural, functional and immunological characteristics of the putative amino acid sequence were predicted by bioinformatics analysis. Our novel finding will contribute to the development of diagnostics for clonorchiasis. These results suggest that immunoproteomic approaches are valuable tools to identify antigens that could be used as targets for effective parasitic infection control strategies.

Prevalence of Clonorchis sinensis infection in dogs and cats in subtropical southern China

BACKGROUND

Clonorchiasis, caused by Clonorchis sinensis, is one of the major parasitic zoonoses in China, particularly in China's southern Guangdong province where the prevalence of C. sinensis infection in humans is high. However, little is known of the prevalence of C. sinensis infection in its reservoir hosts dogs and cats. Hence, the prevalence of C. sinensis infection in dogs and cats was investigated in Guangdong province, China between October 2006 and March 2008.

RESULTS

A total of 503 dogs and 194 cats from 13 administrative regions in Guangdong province were examined by post-mortem examination. The worms were examined, counted, and identified to species according to existing keys and descriptions. The average prevalences of C. sinensis infection in dogs and cats were 20.5% and 41.8%, respectively. The infection intensities in dogs were usually light, but in cats the infection intensities were more serious. The prevalences were higher in some of the cities located in the Pearl River Delta region which is the most important endemic area in Guangdong province, but the prevalences were relatively lower in seaside cities.

CONCLUSIONS

The present investigation revealed a high prevalence of C. sinensis infection in its reservoir hosts dogs and cats in China's subtropical Guangdong province, which provides relevant "base-line" data for conducting control strategies and measures against clonorchiasis in this region.

A brief review of foodborne zoonoses in China

Foodborne zoonoses have a major impact on public health in China. Its booming economy and rapid socioeconomic changes have affected food production, food supplies and food consumption habits, resulting in an increase in the number of outbreaks of foodborne zoonoses. Both emerging and re-emerging foodborne zoonoses have attracted increasing national and international attention in recent years. This paper briefly reviews the main foodborne zoonoses that have had a major impact on public health over the last 20 years in China. The major causative microorganisms, including foodborne bacteria, parasites and viruses, are discussed. The prevention and control of foodborne zoonoses are difficult challenges in China. The information provided here may aid the development of effective prevention and control strategies for foodborne zoonoses.

Distribution of freshwater snails in family-based VAC ponds and associated waterbodies with special reference to intermediate hosts of fish-borne zoonotic trematodes in Nam Dinh Province, Vietnam

Fish-borne zoonotic trematodes, such as Clonorchis sinensis, heterophyids and others, constitute a public health concern in parts of northern Vietnam and infections with these trematodes are often thought to be linked to fish culture. One common fish culture system is the integrated fish-livestock (VAC) ponds where individual households have 1 or more ponds. Fish fry, mainly of various carp species, produced in hatcheries, not necessarily local, are introduced into nursery ponds and after approximately 6 weeks, juvenile fishes are transferred to household ponds, referred to as grow-out ponds. Grow-out ponds are usually fertilized with organic debris, including animal excreta, to stimulate algal growth and subsequently fish growth. This paper describes the distribution of freshwater snails and occurrence of trematode infections in these in VAC ponds and associated habitats as part of a major study on risk factors of FZT infections in cultured fish in two communes, Nghia Lac and Nghia Phu, Nghia Hung District, Nam Dinh Province. The area is under intense rice cultivation with an extensive canal network supplying fields and also household VAC ponds. A total of 16 snail species was found and four were widely distributed i.e. Angulyagra polyzonata, Melanoides tuberculata, Bithynia fuchsiana and Pomacea insularum. Snail diversity and counts were higher in nursery ponds than in grow-out ponds. Species of the families Thiaridae and Viviparidae were more abundant than other species in VAC ponds while species of the Bithyniidae, Stenothyridae and Planorbidae dominated in rice fields and small canals. Trematode infections were found in eight snail species and among these M. tuberculata had the highest overall prevalence of infection (13.28%). No trematode infections were found in species of the Viviparidae and Ampullaridae except for metacercariae. Parapleurolophocercous and pleurolophocercous cercariae constituted the most common type of cercariae recovered, contributing 40.6% of all infections followed by echinostome cercariae (35.0%) and xiphidiocercariae (17.3%). Bithynia fuschiana and M. tuberculata had the most diverse trematode fauna. C. sinensis was not recorded in this study. The VAC pond system in this area, is very important for transmission of minute intestinal trematodes while they play little role in transmission of C. sinensis as its intermediate hosts, bithynid snails, rarely occur in these ponds. From a public health perspective this is positive as the effects of infections with intestinal trematodes are considered mild. On the other hand it is possible that even such subtle effects could have importance in public health as transmission is very intense in the area. And this in combination with the aquaculture importance, reduced marketability of fishes with high metacercariae loads, warrants that control efforts against these trematodes are initiated to reduce transmission in this production system.

Epidemiological investigation of Clonorchis sinensis infection in freshwater fishes in the Pearl River Delta

Pearl River Delta region is a high clonorchiasis-endemic area in China. However, no complete epidemiological data exist regarding its infection in freshwater fishes, an important epidemic factor for Clonorchis sinensis. The present study collected freshwater fishes and shrimps from 32 sites of nine cities in the Pearl River Delta, and the encysted metacercariae of C. sinensis were detected by digesting these specimens with artificial gastric juice. The mean infection rate of freshwater fishes was 37.09% (2,160/5,824) with a mean number of 14.269 encysted metacercariae in every infected fish and 0.460 encysted metacercariae in every gram of fish meat. Of these freshwater fishes, 5,219 were domesticated, and the infection rate was 36.69% with a mean number of 10.743 encysted metacercariae in every infected fish and 0.312 encysted metacercariae in every gram of fish meat; the other 605 were wild, and the infection rate was 40.50% with a mean number of 41.829 encysted metacercariae in every infected fish and 8.812 encysted metacercariae in every gram of fish meat. A total of 228 shrimps were examined, and 3.07% of them were infected with a mean number of 1.00 encysted metacercariae in every infected shrimp. Pseudorasbora parva and Ctenopharyngodon idellus had the highest infection rate and degree of infection in the fishes studied. The results demonstrated a high incidence of C. sinensis infection in freshwater fishes and shrimps within Pearl River Delta region and a great difference in the infection rate among different collection sites and different fish species.

Sensitive and rapid detection of Clonorchis sinensis infection in fish by loop-mediated isothermal amplification (LAMP)

The fish-borne clonorchiasis caused by the oriental liver fluke Clonorchis sinensis is endemic in a number of countries with over 35 million people being infected globally. Rapid and accurate detection of C. sinensis in its intermediate host fish is important for the control and prevention of clonorchiasis in areas where the disease is endemic. In the present study, we established a loop-mediated isothermal amplification (LAMP) approach for the sensitive and rapid detection of C. sinensis metacercariae in fish. The specificity and sensitivity of primers designed from the C. sinensis cathepsins B3 gene were evaluated, and specific amplification products were obtained with C. sinensis, while no amplification products were detected with DNA of related trematodes, demonstrating the specificity of the assay. The LAMP assay was proved to be 100 times more sensitive than a conventional polymerase chain reaction for detection of C. sinensis. The established LAMP assay provides a useful tool for the rapid and sensitive detection of C. sinensis in fish, which has important implications for the effective control of human clonorchiasis.

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 microm. 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.

Display of proteins on Bacillus subtilis endospores

The targeting and anchoring of heterologous proteins and peptides to the outer surface of bacteriophages and cells is becoming increasingly important, and has been employed as a tool for fundamental and applied research in microbiology, molecular biology, vaccinology, and biotechnology. Less known are endospores or spores produced by some Gram-positive species. Spores of Bacillus subtilis are surrounded by a spore coat on their outside, and a few proteins have been identified being located on the outside layer and have been successfully used to immobilize antigens and some other proteins and enzymes. The major advantage of spores over the other published systems is their synthesis within the cytoplasm of the bacterial cell. Therefore, any heterologous protein to be anchored on the outside does not have to cross any membrane. Furthermore, spores are extremely resistant against high temperature, irradiation and many chemicals, and can be stored for many years at room temperature.

Molecular characterization of a novel Clonorchis sinensis secretory phospholipase A(2) and investigation of its potential contribution to hepatic fibrosis

A gene encoding a homologue of phospholipase A(2) was identified from the Clonorchis sinensis adult cDNA plasmid library. The deduced amino acid sequence including a signal peptide that has 28-46% identity with secretory phospholipase A(2), group III (group III sPLA(2)) of other species. It also has typical features of group III sPLA(2)s including 10 cysteines, the key residues of the Ca(2+) loop and catalytic site. The recombinant protein encoded by this gene expressed in Escherichia coli showed a product of about 34kDa in SDS-PAGE. Prediction of signal peptide and Western blot analysis indicated the group III secretory phospholipase A(2) of C. sinensis (CsGIIIsPLA(2)) was an excretory-secretory product (ES product). The enzyme activity of the recombinant protein was determined using phosphatidylcholine as substrates. The result revealed that the protein was a Ca(2+)-dependent PLA(2). Both MTT test and cell cycle analysis of LX-2 showed a higher percentage of cells are in proliferation phase. Semi-quantitative RT-PCR experiments demonstrated an up-regulated expression of collagen III in these cells after incubation with the recombinant protein. We also identified that the recombinant CsGIIIsPLA(2) could bind to some membrane proteins on LX-2 cells specifically by immunofluorescence, thus there might be receptors of CsGIIIsPLA(2) on the LX-2 cell membrane. Our results suggest that CsGIIIsPLA(2) might play an important role in the initiation and development of hepatic fibrosis caused by C. sinensis.

Cost comparison of rapid questionnaire screening for individuals at risk of clonorchiasis in low- and high-prevalence communities in northern Vietnam

Clonorchiasis is an emerging food-borne trematode infection in Vietnam. Due to the absence of cost-effective preventive measures its control largely relies on morbidity reduction by chemotherapy with praziquantel. We performed a comparative cost estimation of three different diagnostic and intervention approaches in areas of high and low prevalence of clonorchiasis in northern Vietnam in order to select more cost-effective chemotherapy. Our study confirmed that a questionnaire investigating the habit of eating raw, freshwater fish was a rapid, cost-effective and operationally feasible tool for identifying individuals at risk of clonorchiasis in both high-prevalence and low-prevalence areas. The cost of diagnosis and intervention per person and per true positive case was 20-fold higher in low-prevalence areas, regardless of the type of approach. Geographical mapping of high-risk areas prior to screening is, therefore, recommended to maximize the cost-effectiveness of the intervention activities.

Molecular genetic profiles among individual Clonorchis sinensis adults collected from cats in two geographic regions of China revealed by RAPD and MGE-PCR methods

Clonorchis sinensis causes the important food-borne zoonosis, clonorchiasis, which is endemic in East Asia, especially in China mainly in Guangdong, Guangxi and Heilongjiang provinces and Korea. Although comparisons on isoenzymes and some molecular profiles of C. sinensis collected from different parts of China and Korea have been studied, few works on the genetic variation among the individuals from different regions of China has been reported. In the present study, individual adults of C. sinensis were collected from cats in two geographic locations (Guangdong province in the South and Heilongjiang province in the North) of China and 44 of them were examined by using random amplified polymorphic DNA (RAPD)-PCR and mobile genetic elements (MGEs)-PCR techniques to assess the individual genetic variability within and between the two groups of this parasite. Six arbitrary primers and two pairs of MGE primers were employed in the genomic DNA amplification. The molecular patterns showed significant polymorphism among the individuals. The RAPD data displayed that the similarity coefficient (SC) of the individuals within Heilongjiang group was much higher than that of the Guangdong group, which was further confirmed by MGE-PCR results. Individuals from Heilongjiang were found genetically closer with lesser polymorphisms than those collected from Guangdong province. These results demonstrated that RAPD and MGE-PCR techniques, particularly RAPD method, could be useful for investigating genetic variations among C. sinensis individuals. They may also indicate that the genetic variation of C. sinensis occurs in the subtropical region--Guangdong--faster than that in the cold-region--Heilongjiang province--due to more generations (life cycle) occurred.

Prevalence, intensity and risk factors for clonorchiasis and possible use of questionnaires to detect individuals at risk in northern Vietnam

A high prevalence of the liver flukes Clonorchis sinensis and Opisthorchis viverrini has been reported in a number of provinces in Vietnam. Knowledge about C. sinensis infection gained from Thailand over the past decade suggests that the habit of eating raw freshwater fish is a major risk factor for infection. However, further information to confirm this is needed. In the present study 1155 villagers in two communes in northern Vietnam were interviewed and their stools were examined for the presence of liver flukes. The prevalence of infection was 26% and was 3.6 times higher in males than in females. The habit of eating raw fish increased the risk of C. sinensis infection 53-fold. These results provide evidence of a strong correlation between the intensity of C. sinensis infection and the cumulative quantity of freshwater fish consumed in a lifetime and suggest that simple questionnaires could be used in endemic areas to quickly identify populations at risk and enable targeted treatment.

Immunogenicity of recombinant Bacillus subtilis spores expressing Clonorchis sinensis tegumental protein

Clonorchis sinensis, which causes clonorchiasis, is of major socioeconomic importance in China. In this study, we report the use of CotC, a major component of the Bacillus subtilis spore coat, as a fusion partner for the expression of C. sinensis TP20.8 (Tegumental Protein 20.8 kDa) on the spore coat. Western blotting was used to identify TP20.8 surface expression on spores. Recombinant spores displaying the TP20.8 antigen were used for oral immunization and were shown to generate mucosal response in rats. TP20.8-specific secretory IgA in feces reached significant levels 2 weeks after oral dosing. This report shows that surface display of recombinant C. sinensis TP20.8 on B. subtilis spores was immunogenic and B. subtilis spores can be used as a mucosal immunization vehicle for parasite prevention and control.