[(CLONORCHIASIS: GLOBAL AND REGIONAL EPIDEMIOLOGY)].

All over the world, much attention is given to the comprehensive studies of parasites and their induced diseases in order to devise effective methods for the diagnosis, treatment, and prevention of parasitic diseases. This review summarizes the information available in the literature on the epidemiology of clonorchiasis caused by the Chinese liver fluke Clonorchis sinensis, including global and regional risk factors for the infection and its transmission. The existing knowledge of this important, but far from the most studied zoonosis, the cause of severe human hepatobiliary diseases, is required for the success of future investigations of parasitic infections.

Rapid detection and differentiation of Clonorchis sinensis and Opisthorchis viverrini using real-time PCR and high resolution melting analysis.

Clonorchis sinensis and Opisthorchis viverrini are both important fish-borne pathogens, causing serious public health problem in Asia. The present study developed an assay integrating real-time PCR and high resolution melting (HRM) analysis for the specific detection and rapid identification of C. sinensis and O. viverrini. Primers targeting COX1 gene were highly specific for these liver flukes, as evidenced by the negative amplification of closely related trematodes. Assays using genomic DNA extracted from the two flukes yielded specific amplification and their identity was confirmed by sequencing, having the accuracy of 100% in reference to conventional methods. The assay was proved to be highly sensitive with a detection limit below 1 pg of purified genomic DNA, 5 EPG, or 1 metacercaria of C. sinensis. Moreover, C. sinensis and O. viverrini were able to be differentiated by their HRM profiles. The method can reduce labor of microscopic examination and the contamination of agarose electrophoresis. Moreover, it can differentiate these two flukes which are difficult to be distinguished using other methods. The established method provides an alternative tool for rapid, simple, and duplex detection of C. sinensis and O. viverrini.

Effects of fish-human transmission and different life stages of fish on Clonorchiasis: A novel mathematical model.

Clonorchiasis is a zoonotic disease mainly caused by eating raw fish and shrimp, and there is no vaccine to prevent it. More than 30 million people are infected worldwide, of which China alone accounts for about half, and is one of the countries most seriously affected by Clonorchiasis. In this work, we formulate a novel Ordinary Differential Equation (ODE) model to discuss the biological attributes of fish within authentic ecosystems and the complex lifecycle of Clonorchis sinensis. This model includes larval fish, adult fish, infected fish, humans, and cercariae. We derive the basic reproduction number and perform a rigorous stability analysis of the proposed model. Numerically, we use data from 2016 to 2021 in Guangxi, China, to discuss outbreaks of Clonorchiasis and obtain the basic reproduction number R0=1.4764. The fitted curve appropriately reflects the overall trend and replicates a low peak in the case number of Clonorchiasis. By reducing the release rate of cercariae in 2018, the fitted values of Clonorchiasis cases dropped rapidly and almost disappeared. If we decrease the transmission rate from infected fish to humans, Clonorchiasis can be controlled. Our studies also suggest that strengthening publicity education and cleaning water quality can effectively control the transmission of Clonorchiasis in Guangxi, China.

[Epizootiological characteristics of clonorchiasis foci in the Amur River ecosystem in the Jewish autonomic region].

Malacofaunal and ichthyoparasitological studies were conducted in the floodplain-river ecosystem in the middle course of the Amur River. The studies covered its channels and tributaries, such as Big and Small Bira, Bidzhan, In, and Vertoprashikha Rivers, in the Birobidzhan, Leninskoye, and Smidovich districts of the Jewish Autonomic Region in the second half of August 2011. It was established that there were biotopes of the mollusk Parafossalurus manchouricus, the first intermediate host of Clonorchis sinensis, in the exosystems of the In, Bira, and Bidzhan Rivers. Sporadic P. manchouricus specimens were found in the Bidzhan channel in the vicinity of its estuary and on the flooded bank of the In River. The bay of the Bira River (the town of Birobidzhan) exhibited a biotope of P. manchouricus with a mollusk population density of 180 to 300 specimens/m2. Seven of 16 examined fish species showed metacercariae of Clonorchis. Among them there were not only Cyprinidae, but also representatives of other families and orders. The two-year-olds of orca-skripuns (Pseudobagrus fulvidraco), orca-whips (Tachysyrus ussuriensis), and Brazhnikov's orsas (Liocassis braschnikowi) were infected with C. sinensis metacercariae. Clonorchis metacercariae were first detected in Amur sleepers (Percottus glehni). This fish species has not been heretofore recorded as the second intermediate host ofC. sinensis. The highest invasion extent for C. sinensis metacercariae was revealed in Amur bitterlings (Rhodeus sericeus) born during the current year. In the biotopes ofdifferent water reservoirs, it changed from 10.0 to 48.0%. In 4 of 6 water reservoirs, Amur bitterlings were found to have larvae of this species of trematodes. The invasion rates were in the range from 1 to 4 metacercariae per fish. Only in individual cases, they were as great as 28 parasitic larvae per fish.

Rapid screening of Clonorchis sinensis infection: Performance of a method based on raw-freshwater fish-eating practice.

Clonorchis sinensis infection is caused by ingestion of raw freshwater fish containing the infective larvae of Clonorchis sinensis. It is highly endemic in East Asia, especially in China. Selective chemotherapy of people who report habitual eating of raw freshwater fish is a control measure. As the performance of this screening technique has not yet been fully evaluated in China, a cross-sectional study was conducted, covering 17 counties in four major clonorchiasis-endemic provinces. About 1 000 participants were enrolled from each county. Fecal samples were collected and examined for helminth eggs and each person enrolled was asked about their practice with respect to eating raw freshwater fish. In total, 16 230 participants from 16 counties were finally included. The overall prevalence of C. sinensis infection was 10.8%, ranging from 0 to 53.7% in the 16 counties, while the percentage of inhabitants eating raw freshwater fish was 26.5%, ranging from 0 to 79.1%. The overall sensitivity and specificity of screening for C. sinensis infection in this approach was 82.3% and 80.3%, respectively, yielding a Youden's index of 0.6. The overall positive and negative likelihood ratios were 4.2 and 0.2, respectively, while the overall positive and negative predictive values were 33.5% and 97.4%, respectively. Furthermore, the sensitivity was higher with regard to high-intensity infections compared to light infections.

High prevalence of Clonorchis sinensis infections and coinfection with hepatitis virus in riverside villages in northeast China.

In China, the prevalence of Clonorchis sinensis (C. sinensis) infections is only evaluated at the provincial level by national sampling surveys, and data from villages and counties are still lacking. In this study, we conducted a cross-sectional survey in 10 villages located along the Lalin River in northeast China. Clonorchiasis was diagnosed using a modified Kato-Katz method that detects the C. sinensis egg in stools. A total of 3,068 persons were screened and 2,911 were recruited for the study. Overall, the prevalence of C. sinensis infection was 29.3%. Among 175 participants who were cured after antiparasitic treatment, 54 (30.86%) were re-infected in this survey. After calibration of potential confounders, male gender, occupation as a farmer, smoking, and occasionally or frequently eating raw fish were independent risk factors for C. sinensis infection. The results of laboratory examinations in the C. sinensis/hepatitis B or C virus co-infection group were similar to those in the hepatitis B or C virus mono-infection groups. In conclusion, C. sinensis is highly endemic in villages along the Lalin River, and the primary route of infection is the consumption of raw freshwater fish. Co-infection with C. sinensis did't aggravate the clinical manifestations of viral hepatitis in this cross-sectional study.

The control of clonorchiasis in Guangdong province, southern China.

Oriental liver fluke disease (clonorchiasis), caused by Clonorchis sinensis, is endemic in 81 counties in Guangdong province, China. This study was conducted following increasing lack of clonorchiasis awareness and increased consumption of raw freshwater fish and raw fish porridge at home and restaurants, which has been attributed to improved living standards in China, and is considered to have led to a higher C. sinensis infection rate in the country. A total of 61,517 individuals were investigated from 123 sites during a provincial survey in 1988, with average C. sinensis infection rate of 1.82% that increased to 4.08% (335/8217) in 1997. Higher infection rate was observed in adult men than women, with heavy infection rate in fishermen and businessmen because they have access and means to get raw fishes for consumption. Thus, clonorchiasis has become a serious public health problem in Guangdong province. Efforts targeting clonorchiasis prevention and control in Guangdong province started in the 1990s. These included carrying out large-scale surveys and chemotherapy in epidemic regions, research on promotion of environmental sanitation and methods for freshwater aquaculture. Establishment and promotion of clonorchiosis demonstration plots for comprehensive control measures, as well as the development of clonorchiasis-prevention community-out-patient clinics were initiated and their effectiveness was evaluated. However, there seem to be no obvious decline in the prevalence of C. sinensis with 4.90% (608/12,401) in 2015, at Guangdong province due to the people's habit of eating raw fishes in endemic areas. This has led to increasing calls to improve environmental sanitation in the aquaculture industry. It is, however, believed that control efforts on clonorchiosis in the province are at an early stage and require strengthening through the cooperation of different departments to work out effective strategies for sustainable field application of control mechanisms.

Experimental model in rats for study on transmission dynamics and evaluation of Clonorchis sinensis infection immunologically, morphologically, and pathologically.

This study aims to gain a better insight into the transmission patterns and immunologic profile of Clonorchis sinensis infection and make a headway on the pathogenesis regarding cholangiocarcinoma and hepatic lesions. Experimental models orally infected by C . sinensis metacercariae were constructed in rats. Immunological assays were performed to measure serum level of IgA, IgE, IgG1, IgG2a, IFN-gamma, and IL-4. Infection parameters were assessed by worm recovery rate, eggs per gram faece and worm size. Pathological sections with livers were managed with immunofluorescence, hematoxylin, eosin, and Masson's trichrome staining to evaluate the hepatic pathological changes. Interestingly, rats infected with only one C . sinensis metacercariae even gained a high worm recovery rate of 83.3% compared with rats infected with more metacercariae. Serological changes according to different infection doses indicated that immune response presented a tendency to Th2 type by expressing transient high level of IgG1, IL-4, and IgE. Hepatic tissues appeared inflammatory and fibrotic, revealed by different stainings. Intrahepatic bile ducts displayed cholangiectasis and proliferation with excreted/secreted antigen histologically located. C . sinensis, as a fish-borne zoonosis, presented novel transmission patterns which explained high infection rate in endemic areas; infection rate of C . sinensis was frequency-dependent and dose-related. Humoral immunity played a prevalent role in resisting to C . sinensis based on the rat models. C . sinensis infection played an undoubted role in biliary and hepatic diseases.

Mathematical modeling the dynamics of Clonorchiasis in Guangzhou City of China.

In this paper, we have set up a mathematical model on the basic life cycle of clonorchiasis to fit the data of human clonorchiasis infection ratios of Guangzhou City of Guangdong Province in China from 2006-2012. By this model, we have proved that the condition of the basic reproductive number R0>1 or R0<1 corresponds the globally asymptotically stable of the endemic equilibrium or the disease-free equilibrium, respectively. The basic reproductive number is estimated as 1.41 with those optimal parameters. Some efficient strategies to control clonorchiasis are provided by numerical analysis of the mathematical model.

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.

The role of evolutionary biology in research and control of liver flukes in Southeast Asia.

Stimulated largely by the availability of new technology, biomedical research at the molecular-level and chemical-based control approaches arguably dominate the field of infectious diseases. Along with this, the proximate view of disease etiology predominates to the exclusion of the ultimate, evolutionary biology-based, causation perspective. Yet, historically and up to today, research in evolutionary biology has provided much of the foundation for understanding the mechanisms underlying disease transmission dynamics, virulence, and the design of effective integrated control strategies. Here we review the state of knowledge regarding the biology of Asian liver Fluke-host relationship, parasitology, phylodynamics, drug-based interventions and liver Fluke-related cancer etiology from an evolutionary biology perspective. We consider how evolutionary principles, mechanisms and research methods could help refine our understanding of clinical disease associated with infection by Liver Flukes as well as their transmission dynamics. We identify a series of questions for an evolutionary biology research agenda for the liver Fluke that should contribute to an increased understanding of liver Fluke-associated diseases. Finally, we describe an integrative evolutionary medicine approach to liver Fluke prevention and control highlighting the need to better contextualize interventions within a broader human health and sustainable development framework.

Investigation on the epidemiological factors of Clonorchis sinensis infection in an area of south China.

To detect the epidemiological factors of Clonorchis sinensis infection in Hengxian County, one of counties in Guangxi Zhuang Autonomous Region where Schistosoma japonicum was endemic but eliminated in the late 1980s, a questionnaire was designed with 37 questions covering socioeconomic conditions and human behavior, contamination of the environment and fish ponds, inadequate farming/fishery practices; and the formalin-ether sedimentation technique was used to examine the feces of cats, dogs and pigs for the eggs of C. sinensis. Fresh fish was sliced and digested to detect the metacercariae of C. sinensis under a stereomicroscope. Of 1,521 people interviewed, 64% of the interviewees did not know about fluke disease or its transmission route, 46% of those who knew about the fluke believed that the infection caused no harm or only slight harm to their health. More than half of the interviewees (51%) ate raw fish at least 1-2 times per month, more among the middle-aged males. Eight percent of them used the same utensils for both raw fish and cooked food. When advice was given not to eat raw fish, 73% of the interviewees thought it was not feasible. In relation to pisciculture, 25% and 9% of the owners of fish ponds fed their fish with feces of domestic animals and human feces, respectively. The prevalences of C. sinensis infection in cats, dogs and pigs were 70, 50 and 27%, respectively, and the infection rate in fish was 40%. These results indicate the poor knowledge, and beliefs, and unhealthy behaviors in the human population. They also show poor environmental hygiene and inappropriate farming/fishery practices are important in the increase of C. sinensis prevalence in humans. Combined interventions, including health education, environmental modification, reform of traditional farming/fishery practices, mass screening and chemotherapy for humans, and the management of domestic animals are needed in developing control strategies to decrease C. sinensis infection in the human population.

Viability of metacercariae of Clonorchis sinensis in frozen or salted freshwater fish.

Metacercariae of Clonorchis sinensis were collected from freshwater fish (Pseudorasbora parva) after storage in a freezer at -12 degrees C for 10-20 days, in a freezer at -20 degrees for 3-7 days, or treating with heavy salt (fish/salt = 10 gm/3 gm) at 26 degrees for 5-15 days. The metacercariae from the frozen fish were inoculated into 30 rats and eight rabbits, and those from the salted fish into 33 rats. Metacercariae from freshwater fish stored at -12 degrees for 10-18 days or -20 degrees for 3-7 remained viable and infective. Moreover, those kept at the heavy salt concentration for 5-7 days remained viable and infective. These findings indicate that freezing or storing infected freshwater fish in heavy salt may not be effective in the prevention of clonorchiasis. However, it appears that refrigeration, or keeping the fish in salt for longer periods, may be suitable for prevention of the infection.

Epidemiology of clonorchiasis in Ninh Binh Province, Vietnam.

Clinical and stool examinations for clonorchiasis were carried out in an endemic area, Kim Son District, Ninh Binh Province, Vietnam. Stool examination with the Kato-Katz technic revealed that in 306 residents selected randomly, 42 people (13.7%) were infected with Clonorchis sinensis. The rate was biased towards men (23.4%) as opposed to women (1.5%) and increased with age. No children younger than 10 years old were infected, reflecting difference in a chance for acquisition of infection through a habit of eating raw fish. Few clinical abnormalities were found by blood and urine examinations of the patients. Treatment with praziquantel decreased the infection rate to 5.3% at 6 weeks later. Snails, Melanoides tuberculatus, collected from ponds around the settlements were infected with cercariae at a rate of 13.3%. Farmed fish (Hypophthalmichtys molitrix) in the ponds were infected with metacercariae at rates of 56.4% in small individuals and 100% in large ones. The life cycle of C. sinensis is exclusively completed in the ponds and the traditional habit of eating raw fish in summer was thought to be a major route of infection.

Epidemiologic characteristics of Clonorchiasis sinensis in Guandong Province, China.

Extensive survey of the distribution of the liver fluke Clonorchis sinensis in Guandong Province, China, has revealed high frequencies in human populations in some areas and absence in others. The distribution relates in part to the demography of first and second intermediate hosts and animal reservoir hosts, but it relates more clearly to the differing food habits of various populations in particular geographic areas. Thus clonorchiasis is concentrated in the Zhu Jiang (Pearl River) delta and along the Han Jiang (Han River) but is absent in the Leizhou Peninsula and in the western region of the province. Males tend to have higher infection rates than females. Age distribution is not uniform: in some communities infection rates increase with age where adults eat raw or undercooked fish, while in other infections reaches its peak in early teenage children and declines thereafter where children eat small raw fish but the habit does not persist into adult life. While there is some evidence that high C. sinensis rates correlate with high liver cancer rates and vice versa, this issue requires in depth investigation at community level to differentiate hepatocellular carcinoma and early cholangiocarcinoma, since it is possible that C. sinensis infection promotes higher risk of the latter form of liver cancer.

Snail-borne parasitic zoonoses in Korea.

A total of 22 snail-borne parasites causing various parasitic zoonoses in Korea are listed and reviewed. All of these parasites are indigenous except Heterophyes heterophyes, H. dispar and Angiostrongylus cantonensis detected in patients who traveled outside of Korea.

[Clinico-parasitological research in a mixed focus of clonorchiasis and intestinal nematodiasis in Hanamnin Province (the Socialist Republic of Vietnam)]. / Kliniko-parazitologicheskie issledovaniia v smeshannom ochage klonorkhoza i kishechnykh nematodozov v provintsii Khanamnin' (SRV).

The authors described the clonorchiasis focus in the Vietnam province at the seaside delta of the Red River where the aforementioned invasion was accompanied with multiple invasions with intestinal nematodes. Clonorchiasis infestation rate was 28.4% ascaridiasis, 50.5%, trichocephaliasis, 21.3% ancylostomiasis, 7.0%. Clonorchiasis invasion was the result of consumed uncooked carp fish in the salad. It was revealed that the fish was reared in the ponds near the settlements and was fed untreated human and animal feces. The meal was more common among the male persons in the presence of the alcohol intake. Clinical symptoms of the mixed clonorchiasis and intestinal nematodiasis invasion was featured by pains, dyspepsia and the asthenoneurotic syndrome.

The zoonotic, fish-borne liver flukes Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini.

Clonorchis sinensis, Opisthorchis felineus and Opisthorchis viverrini are the three most important liver flukes involved in human health, infecting more than 45 million people worldwide. Both C. sinensis and O. viverrini, and possibly O. felineus, can induce human cholangiocarcinoma as well as inducing other hepatobiliary pathology. Although the life cycles of all three species are similar, only that of O. felineus in Europe remains predominantly zoonotic, while O. felineus in Asia and C. sinensis have a stronger mixture of zoonotic and anthroponotic components in their life cycles. Opisthorchis viverrini from the Mekong area of southeastern Asia is predominantly anthroponotic. Here we discuss the comparative epidemiology of these three taxa comparing in detail the use of first, second and final animal hosts, and consider the potential role of humans in spreading these pathogens. In addition we discuss the genetic structure of all three species in relation to potentially cryptic species complexes.

[Status of Clonorchis sinensis infection and its influencing factors among migrant workers in Baoan District, Shenzhen City].

OBJECTIVE: To understand the status of Clonorchis sinensis infection and its risk factors among migrant workers in Baoan District of Shenzhen City, so as to provide the evidence for the development of control strategies. METHODS: A total of 642 migrant workers were chosen as the investigation samples by the stratified cluster sampling method. Their sera were collected and tested for Clonorchis sinensis infection with ELISA, and a questionnaires survey was performed to collect the information of clonorchiasis sinensis related to knowledge and behaviors. The influencing factors were summarized with the case-control study method. RESULTS: A total of 642 subjects were investigated, in which 530 subjects received the serological examinations and the positive rate was 6.6% (35/530). The significant differences were not found between genders (Chi2 = 1.19, P = 0.28) or among the age groups (Chi2 = 0.45, P = 0.80). The awareness rates of knowing infection route, health hazard and prevention knowledge were 50.16%, 33.64% and 27.41%, respectively. The rates of healthy behaviors such as not eating semi-cooked fish, not feeding pets with raw fish or shrimps, and differentiating between the raw and cooked food when using cutting boards were 80.67%, 78.41% and 45.95%, respectively. The awareness rate of prevention knowledge was positively related to the infection (OR = 0.16, P < 0.01). CONCLUSION: The prevention and control of Clonorchis sinensis infection among migrant workers could not be neglected, and the health education should be strengthened.