Field survey focused on Opisthorchis viverrini infection in five provinces of Cambodia

Prevalence and distribution of trematodes hosted by Bithynia siamensis in Southern Thailand

This study aimed to investigate the occurrence of larval trematode infections in bithyniid snails across five provinces in southern Thailand. A total of 1,413 Bithynia siamensis snails were collected between October 2021 and October 2022 using handpicking and scooping methods. Among these, 844 were identified as B. s. siamensis and 569 as B. s. goniomphalos. The snail samples were examined for parasitic infections in the laboratory using shedding and crushing methods. Among the 27 sampling sites, snails from 6 sites were infected with various trematode species (infection rate: 4.95%, 70/1,413). Evaluation of the morphological and internal organ characteristics of the cercariae allowed for the categorization of the trematodes into five species of trematodes (belonging to four families). The identified species included Echinochasmus pelecani (family: Echinostomatidae), Echinostoma revolutum (family: Echinostomatidae), Haematoloechus similis (family: Haematoloechidae), Loxogenoides bicolor (family Lecithodendriidae), and Stictodora tridactyla (family: Heterophyidae), and the infection rates for these species were 3.26% (46/1,413), 0.35% (5/1,413), 0.42% (6/1,413), 0.78% (11/1,413), and 0.14% (2/1,413), respectively. The cercariae from the identified trematode species were studied for DNA analysis. The phylogenetic lineage reveals relationships among the species, confirming the morphological distinctions.

Multi-epitope protein production and its application in the diagnosis of opisthorchiasis

BACKGROUND

Opisthorchiasis and cholangiocarcinoma (CCA) continue to be public health concerns in many Southeast Asian countries. Although the prevalence of opisthorchiasis is declining, reported cases tend to have a light-intensity infection. Therefore, early detection by using sensitive methods is necessary. Several sensitive methods have been developed to detect opisthorchiasis. The immunological detection of antigenic proteins has been proposed as a sensitive method for examining opisthorchiasis.

METHODS

The Opisthorchis viverrini antigenic proteins, including cathepsin B (OvCB), asparaginyl endopeptidase (OvAEP), and cathepsin F (OvCF), were used to construct multi-antigenic proteins. The protein sequences of OvCB, OvAEP, and OvCF, with a high probability of B cell epitopes, were selected using BepiPred 1.0 and the IEDB Analysis Resource. These protein fragments were combined to form OvCB_OvAEP_OvCF recombinant DNA, which was then used to produce a recombinant protein in Escherichia coli strain BL21(DE3). The potency of the recombinant protein as a diagnostic target for opisthorchiasis was assessed using immunoblotting and compared with that of the gold standard method, the modified formalin-ether concentration technique.

RESULTS

The recombinant OvCB_OvAEP_OvCF protein showed strong reactivity with total immunoglobulin G (IgG) antibodies against light-intensity O. viverrini infections in the endemic areas. Consequently, a high sensitivity (100%) for diagnosing opisthorchiasis was reported. However, cross-reactivity with sera from other helminth and protozoan infections (including taeniasis, strongyloidiasis, giardiasis, E. coli infection, enterobiasis, and mixed infection of Echinostome spp. and Taenia spp.) and no reactivity with sera from patients with non-parasitic infections led to a reduced specificity of 78.4%. In addition, the false negative rate (FNR), false positive rate (FPR), positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy were 0%, 21.6%, 81.4%, 100%, and 88.9%, respectively.

CONCLUSIONS

The high sensitivity of the recombinant OvCB_OvAEP_OvCF protein in detecting opisthorchiasis demonstrates its potential as an opisthorchiasis screening target. Nonetheless, research on reducing cross-reactivity should be undertaken by detecting other antibodies in other sample types, such as saliva, urine, and feces.

Clonorchiasis and opisthorchiasis: epidemiology, transmission, clinical features, morbidity, diagnosis, treatment, and control

Clonorchis sinensis, Opisthorchis viverrini, and Opisthorchis felineus are important liver flukes that cause a considerable public health burden in eastern Asia, southeastern Asia, and eastern Europe, respectively. The life cycles are complex, involving humans, animal reservoirs, and two kinds of intermediate hosts. An interplay of biological, cultural, ecological, economic, and social factors drives transmission. Chronic infections are associated with liver and biliary complications, most importantly cholangiocarcinoma. With regard to diagnosis, stool microscopy is widely used in epidemiologic surveys and for individual diagnosis. Immunologic techniques are employed for screening purposes, and molecular techniques facilitate species differentiation in reference laboratories. The mainstay of control is preventive chemotherapy with praziquantel, usually combined with behavioral change through information, education and communication, and environmental control. Tribendimidine, a drug registered in the People's Republic of China for soil-transmitted helminth infections, shows potential against both C. sinensis and O. viverrini and, hence, warrants further clinical development. Novel control approaches include fish vaccine and biological control. Considerable advances have been made using multi-omics which may trigger the development of new interventions. Pressing research needs include mapping the current distribution, disentangling the transmission, accurately estimating the disease burden, and developing new diagnostic and treatment tools, which would aid to optimize control and elimination measures.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts is important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes and hence contribute to reduction of CCA in endemic areas.

High endemicity of Opisthorchis viverrini infection among people in northern Cambodia confirmed by adult worm expulsion

Opisthorchis viverrini infection is an emerging disease in Cambodia, especially in central and southeastern areas. However, its status in northern areas bordering Lao PDR has been relatively unknown. The present study was performed to investigate the status of O. viverrini infection among people in Preah Vihear and Stung Treng provinces through fecal examination to detect eggs and recovery of adult flukes from some of the egg-positive cases. Fecal examinations were performed on a total of 1101 people from 10 villages in the 2 provinces using the Kato-Katz thick smear technique. For recovery of adult flukes and other helminth parasites 10 volunteers positive for eggs of Opisthorchis viverrini and/or minute intestinal flukes (Ov/MIF), in Kampong Sangkae village, Preah Vihear province, were administered a single oral dose of 40 mg/kg praziquantel plus 5-10 mg/kg of pyrantel pamoate and purged with 40-50 g magnesium salts. Adult trematodes, together with nematodes and cestodes expelled in diarrheic stools were collected under a stereomicroscope or with the naked eye. The proportion of egg-positive cases for overall liver and intestinal helminths was high but not notably different between the 2 provinces, 65.5% in Preah Vihear versus 64.7% in Stung Treng. The average proportion of Ov/MIF egg-positive cases was 59.8%. A total of 315 adult specimens of O. viverrini were recovered from the 10 volunteers (4-98 specimens per individual; mean, 32). A smaller number of Haplorchis taichui adults, an intestinal fluke, were found mixed-infected in 7 (103 specimens in total; 1-31 per individual; mean, 15) of the 10 volunteers. Adult specimens of hookworms, Enterobius vermicularis, Trichostrongylus sp., and a Taenia tapeworm strobila were recovered in some cases. Based on the results, it has been confirmed that the surveyed areas in Preah Vihear and Stung Treng provinces, Cambodia, are highly endemic areas of O. viverrini infection with a low-grade mixed infection with H. taichui.

Opisthorchis viverrini-Current Understanding of the Neglected Hepatobiliary Parasite

Opisthorchiasis due to Opisthorchis viverrini infection continues to be a significant public healthcare concern in various subregions of Southeast Asia, particularly in Thailand, Laos, Cambodia, Myanmar, and Vietnam. The main mode of transmission is via consumption of raw or undercooked fish, which is deeply embedded in the culture and tradition of the people living near the Mekong River. After ingestion, the flukes migrate to the bile ducts, potentially causing many hepatobiliary complications, including cholangitis, cholecystitis, cholelithiasis, advanced periductal fibrosis and cholangiocarcinoma. Several mechanisms of opisthorchiasis-associated cholangiocarcinogenesis have been proposed and elucidated in the past decade, providing insight and potential drug targets to prevent the development of the sinister complication. The gold standard for diagnosing opisthorchiasis is still via stool microscopy, but the advent of novel serological, antigen, and molecular tests shows promise as more convenient, alternative diagnostic methods. The mainstay of treatment of opisthorchiasis is praziquantel, while treatment of opisthorchiasis-associated cholangiocarcinoma depends on its anatomic subtype and resectability. Thus far, the most successful fluke control programme is the Lawa model based in Thailand, which raised awareness, incorporated education, and frequent surveillance of intermediate hosts to reduce transmission of opisthorchiasis. Development of vaccines using tetraspanins shows promise and is currently ongoing.

Global prevalence of 4 neglected foodborne trematodes targeted for control by WHO: A scoping review to highlight the gaps

BACKGROUND

Foodborne trematodiases (FBTs) are a group of trematodes targeted for control as part of the World Health Organization (WHO) road map for neglected tropical diseases from 2021 to 2030. Disease mapping; surveillance; and capacity, awareness, and advocacy building are critical to reach the 2030 targets. This review aims to synthesise available data on FBT prevalence, risk factors, prevention, testing, and treatment.

METHODS

We searched the scientific literature and extracted prevalence data as well as qualitative data on the geographical and sociocultural risk factors associated with infection, preventive/protective factors, and methods and challenges of diagnostics and treatment. We also extracted WHO Global Health Observatory data representing the countries that reported FBTs during 2010 to 2019.

RESULTS

One hundred and fifteen studies reporting data on any of the 4 FBTs of focus (Fasciola spp., Paragonimus spp., Clonorchis sp., and Opisthorchis spp.) were included in the final selection. Opisthorchiasis was the most commonly reported and researched FBT, with recorded study prevalence ranging from 0.66% to 88.7% in Asia, and this was the highest FBT prevalence overall. The highest recorded study prevalence for clonorchiasis was 59.6%, reported in Asia. Fascioliasis was reported in all regions, with the highest prevalence of 24.77% reported in the Americas. The least data was available on paragonimiasis, with the highest reported study prevalence of 14.9% in Africa. WHO Global Health Observatory data indicated 93/224 (42%) countries reported at least 1 FBT and 26 countries are likely co-endemic to 2 or more FBTs. However, only 3 countries had conducted prevalence estimates for multiple FBTs in the published literature between 2010 to 2020. Despite differing epidemiology, there were overlapping risk factors for all FBTs in all geographical areas, including proximity to rural and agricultural environments; consumption of raw contaminated food; and limited water, hygiene, and sanitation. Mass drug administration and increased awareness and health education were commonly reported preventive factors for all FBTs. FBTs were primarily diagnosed using faecal parasitological testing. Triclabendazole was the most reported treatment for fascioliasis, while praziquantel was the primary treatment for paragonimiasis, clonorchiasis, and opisthorchiasis. Low sensitivity of diagnostic tests as well as reinfection due to continued high-risk food consumption habits were common factors.

CONCLUSION

This review presents an up-to-date synthesis on the quantitative and qualitative evidence available for the 4 FBTs. The data show a large gap between what is being estimated and what is being reported. Although progress has been made with control programmes in several endemic areas, sustained effort is needed to improve surveillance data on FBTs and identify endemic and high-risk areas for environmental exposures, through a One Health approach, to achieve the 2030 goals of FBT prevention.

RAW ATTITUDES: Socio-Cultures, Altered Landscapes, and Changing Perceptions of an Underestimated Disease

Raw attitudes relate to the food cultures, eating habits, and behaviours of people in relation to the consumption of raw, partially cooked, and fermented freshwater fish dishes, which puts people at risk of Ophistochis viverrini and other parasitic infections. The chapter reviews raw attitudes within the countries and across the borders of the greater Mekong region, particularly northeast Thailand, Lao PDR, Vietnam, and Cambodia. Rather than treat each nation-state as an isolated epidemiological box, the chapter explores transborder complexity in relation to multiple anthropogenic transformations to the landscapes of the region and developmental impacts upon ecosystems and life cycles. Economic projects such as multiple hydropower dams, irrigation schemes, water-diversions, roads, and aquaculture ponds have significant impacts on FTZ life-cycle dynamics. In addition, many ecological changes are transboundary ones, and there are added complications relating human mobility, altered agrarian landscapes, and significant numbers of migrant workers. The chapter also examines public health programmes and educational interventions which are altering perceptions of O. viverrini and cholangiocarcinoma over time. A key argument is the need for transdisciplinary scientific and social science strategies alongside multi-pronged health interventions, such as 'the CASCAP model'. There exist many unknowns and gaps relating to widespread anthropogenic modifications upon life cycles, upon lifestyles, livelihoods, and human behaviours, which require research projects that span socio-economic, ecological, geographical, and public health dynamics of disease.

Susceptibility patterns of Bithynia siamensis siamensis and Bithynia funiculata to Opisthorchis viverrini infection: an indication of the risk of opisthorchiasis transmission in non-endemic areas

Among the snail species acting as hosts for medically significant trematodes, only three taxa of Bithynia are responsible for transmitting the carcinogenic liver fluke Opisthorchis viverrini to humans in different geographical areas. Although B. siamensis goniomphalos is the primary species responsible for O. viverrini transmission in endemic areas, B. siamensis siamensis and B. funiculata remain potential hosts for transmission. This study objects to determine the susceptibility of B. siamensis siamensis and B. funiculata to O. viverrini to assess the risk of O. viverrini transmission in non-endemic areas. The snails of both species were first introduced to O. viverrini eggs, after which O. viverrini infection was investigated using specific PCR primers after a period of 1, 7, 14, 28, and 56 days post-infection (dpi). Opisthorchis viverrini infection in both B. siamensis siamensis and B. funiculata was high in the early period (1 and 7 dpi) while decreasing over time. It was also shown that the odds of susceptibility to O. viverrini infection in B. siamensis siamensis were 64.5% higher relative to the odds of susceptibility in B. funiculata (P < 0.05). Results of this study provide an early insight into the Bithynia-Opisthorchis relationship and thus have great potential to assess risk and raise awareness of opisthorchiasis in non-endemic regions, especially in regions endemic for B. siamensis siamensis.

Current status of human liver fluke infections in the Greater Mekong Subregion

The Greater Mekong Subregion (GMS) is a trans-national region of the Mekong River basin in Southeast Asia comprising Cambodia, the People's Republic of China (specifically Yunnan Province and Guangxi Zhuang Autonomous Region), Lao People's Democratic Republic (Lao PDR), Myanmar, Thailand, and Vietnam home to more than 340 million people or almost 4.5% of the global population. Human liver fluke infections caused by Opisthorchis viverrini and Clonorchis sinensis have been major public health problems in this region for decades. Opisthorchiasis caused by O. viverrini is prevalent in Thailand, Lao PDR, Cambodia and central-southern Vietnam with more than 12 million people infected. Clonorchiasis caused by C. sinensis is endemic in northern Vietnam and Guangxi with estimated 3.5 -5 million infected. The infections can cause several liver and biliary diseases such as cholangitis, periductal fibrosis, gallstones, and cholangiocarcinoma (CCA), a fatal bile duct cancer. Key determinants of the geographical distribution differences of the two liver fluke species are snail species and geographic barriers. Main risk behaviour of the infections is the culture of eating raw fish "the raw attitude" of people in the GMS, especially the Tai/Dai/Thai/Laos ethnic groups, the major population in the GMS. Over the past 20 years, there is a big change in prevalence of the infections. Opisthorchiasis has long been endemic, particularly in northern and northeastern Thailand and Lao PDR with over 8-10 million cases estimated. However, after several rounds of national campaign against opisthorchiasis using integrated control approach in Thailand over the past three decades, the prevalence of O. viverrini infection has reduced from over 15% in 1996 to 2.2% in 2019. High prevalence of O. viverrini infection continues in Lao PDR and central Vietnam. Emerging high prevalence, up to a maximum of 47.5%, has been noted in Cambodia during the past 10 years possibly due to more studies being conducted rather than increasing prevalence. O. viverrini infection has now also been reported in Lower Myanmar in recent years. Clonorchiasis has been known in northern Vietnam and southern China for a long time. Several surveys have reported infections in Guangxi in the last 10 years, and until now liver fluke infected cases have not been reported in Yunnan. Overall, nowadays, there is a shift in high risk areas for GMS liver fluke infection from northeastern Thailand to Lao PDR, Cambodia, Vietnam, Myanmar, and Guangxi P.R. China. Urgent systematic disease mapping and integrated liver fluke control using One Health approaches should be implemented nationwide in GMS countries.

Prevalence and Intensity of Opisthorchis viverrini Metacercarial Infection in Fish from Phnom Penh, Takeo, and Kandal Provinces, Cambodia

The prevalence and intensity of Opisthorchis viverrini metacercariae (OvMc) were investigated in fish from 3 southern administrative regions along the Mekong River in Cambodia, i.e., Phnom Penh, Takeo, and Kandal Provinces from 2017 to 2020. A total of 295 freshwater fish (24 species) were transported to our laboratory with ice and examined using the artificial digestion method. In Phnom Penh, among 4 fish species positive for OvMc, 9 (23.7%) of 38 specimens examined were infected, and their intensity of infection averaged 4.3 metacercariae per infected fish. In Takeo Province, among 10 fish species positive for OvMc, 24 (38.1%) out of 63 fish examined were infected, and their intensity of infection was av. 14.4 metacercariae per infected fish. In particular, all of 3 Osteochilus schlegelii fish examined were infected, and their infection intensity was high, 34.7 metacercariae per fish. In Kandal Province, among 6 fish species positive for OvMc, 46 (90.2%) out of 51 specimens examined were infected, and their infection intensity was 24.0 metacercaraie per infected fish. All fish of Systomus orphoides (n=17), Barbonymus altus (n=14), and Rasbora aurotaenia (n=2) were infected, and their intensity of infection averaged 37.7, 21.6, and 18.5 metacercariae per fish, respectively. Metacercariae of Haplochis yokogawai, Haplorchis taichui, and Centrocestus formosanus were detected in fish from Takeo and Kandal Provinces. From these results, it has been confirmed that a variety of fish species from Phnom Penh, Takeo, and Kandal Provinces are commonly infected with OvMc, and preventive measures to avoid human O. viverrini infection should be performed in Cambodia.

Epidemiology and determinants of clonorchiasis in school children in southeastern China

Clonorchiasis is an important food-borne parasitic disease in China because of the popularity in ingesting raw freshwater fish. To explore the epidemiology and determinants of clonorchiasis in children, a cross-sectional survey was implemented in two middle schools in Qiyang county, Hunan province, in southeastern China. Questionnaire survey and fecal examination were implemented. Questionnaires were fed back by 627 students, while stool samples were collected from 557 students, out of which 545 ones also provided questionnaire information. The percentage of students ingesting raw freshwater fish was 40.5% (254/627), while the prevalence with Clonorchis sinensis infection was 18.9% (105/557). Such factors contributed significantly to the students' practice in eating raw freshwater fish including boys, fathers' eating raw freshwater fish, mothers' eating raw freshwater fish, and preparation of raw freshwater fish at home, with an adjusted odds ratio of 1.9 (95% confidence intervals (95% CI): 1.3-2.8), 3.9 (95% CI: 2.3-6.5), 3.0 (95% CI: 1.8-4.8) and 2.8 (95% CI: 1.8-4.5), correspondingly. Ingestion of raw freshwater fish, fathers' eating raw freshwater fish and preparation of raw freshwater fish at home were risk factors of C. sinensis infection in students, and the adjusted odds ratio was 3.2 (95% CI: 1.9-5.5), 2.1 (95% CI: 1.1-3.9) and 1.8 (95% CI: 1.0-3.2), respectively. Thus, clonorchiasis was endemic in the surveyed schools due to the ingestion of raw freshwater fish, which is influenced by family environment. Education should be implemented in schools to promote behavioral change of eating raw freshwater fish.

Model-based spatial-temporal mapping of opisthorchiasis in endemic countries of Southeast Asia

Opisthorchiasis is an overlooked danger to Southeast Asia. High-resolution disease risk maps are critical but have not been available for Southeast Asia. Georeferenced disease data and potential influencing factor data were collected through a systematic review of literatures and open-access databases, respectively. Bayesian spatial-temporal joint models were developed to analyze both point- and area-level disease data, within a logit regression in combination of potential influencing factors and spatial-temporal random effects. The model-based risk mapping identified areas of low, moderate, and high prevalence across the study region. Even though the overall population-adjusted estimated prevalence presented a trend down, a total of 12.39 million (95% Bayesian credible intervals [BCI]: 10.10–15.06) people were estimated to be infected with O. viverrini in 2018 in four major endemic countries (i.e., Thailand, Laos, Cambodia, and Vietnam), highlighting the public health importance of the disease in the study region. The high-resolution risk maps provide valuable information for spatial targeting of opisthorchiasis control interventions.

Very low prevalence of Opisthorchis viverrini s.l. cercariae in Bithynia siamensis siamensis snails from the canal network system in the Bangkok Metropolitan Region, Thailand

The liver fluke Opisthorchis viverrini s.l. is associated with a long-term public health problem in Thailand. However, O. viverrini s.l. infection in Bithynia snails in the canal network system (CNS) in the Bangkok Metropolitan Region (BMR) has never been assessed. This study aimed to investigate the occurrence of B. siamensis siamensis and the prevalence of O. viverrini s.l. infection in this snail in the CNS in BMR along with morphological examination and molecular analyses on O. viverrini s.l. cercariae. The snails were randomly sampled from the CNS in all BMR areas from January 2018 to July 2019. Snail specimens were identified and examined for digenean infection by shedding and dissection. The cercariae were identified using morphology and molecular methods, including PCR with a species-specific primer and a Bayesian phylogenetic analysis of ITS2 sequences. Bithynia siamensis siamensis was found in almost all sampling localities, with different quantities and detected frequencies. From a total of 7473 B. s. siamensis specimens, O. viverrini s.l. infections were detected in the Northern Bangkok, Muang Nakhon Pathom, Krathum Baen, and Lam Luk Ka areas with an overall prevalence of 0.05% (4/7473) and prevalence of 0.22% (1/455), 0.21% (1/469), 0.40% (1/253), and 0.16% (1/614) in individual localities with positive snails, respectively. This study is the first investigation of digenean infection in the canal network system-type habitat in Thailand and revealed extremely low O. viverrini s.l. prevalence.

Discovery of Carcinogenic Liver Fluke Metacercariae in Second Intermediate Hosts and Surveillance on Fish-Borne Trematode Metacercariae Infections in Mekong Region of Myanmar

Countries of lower Mekong regions are highly alarmed by the spread of fish-borne trematode infections, i.e., small liver flukes and minute intestinal flukes especially in Thailand, Lao People’s Democratic Republic (Lao PDR), Vietnam, Cambodia and Myanmar. Moreover; the incidence of cholangiocarcinoma has also been increasing in the endemic area of liver fluke infections. Only a few reports have been published concerning the fish-borne trematodes infections in the central region of Myanmar. However; there is still a lack of information regarding the status of trematodes infections in second intermediate hosts in the Mekong region of Myanmar. Therefore, we conducted surveillance on the distribution of trematode metacercariae in small cyprinoid fishes collected from the Mekong region of Myanmar. A total of 689 fishes (12 different species of cyprinoid fishes) have been collected and examined by pepsin digestion methods. We discovered four species of fish-borne trematode metacercariae infections, i.e., carcinogenic liver fluke, Opisthorchis viverrini; minute intestinal flukes, Haplorchis taichui; Haplorchis pumilio and Haplorchoides sp. in Tachileik, the Mekong Region of Myanmar. The outcome of this study could be a useful index for the fish-borne zoonotic trematode epidemiology in the Mekong area. Besides, the results of our study contribute to filling the gap of information necessary for the control and prevention of fish-borne trematode zoonotic infections in the Mekong region.

Recent advances on the immunobiology of Bithynia spp. hosts of Opisthorchis viverrini

This article reviews the past and present scientific reports regarding Bithynia spp. focusing on the biology, ecology and life cycle of Bithynia snails and their responses to Opisthorchis viverrini infection. Moreover, new data regarding comparative molecular genomics and proteomic approaches have recently revealed novel molecular components involved in the immune defence responses from Bithynia spp., providing additional perspectives for future studies. Studies on the specific interaction between Bithynia snails and their trematodes will contribute to further understanding the snail-parasite relationship with regards to epidemiology and control of Opisthorchiasis and broaden the scope on comparative immunology of gastropod snails.

Genetic structure and geographical variation of Bithynia siamensis goniomphalos sensu lato (Gastropoda: Bithyniidae), the snail intermediate host of Opisthorchis viverrini sensu lato (Digenea: Opisthorchiidae) in the Lower Mekong Basin revealed by mitochondrial DNA sequences

The freshwater snail Bithynia siamensis goniomphalos sensu lato is widely distributed in the Lower Mekong Basin where it acts as the first intermediate host of the liver fluke Opisthorchis viverrini, a group 1 carcinogen causing cholangiocarcinoma. This study explores the genetic structure and geographical variation of B. s. goniomphalos from eight previously studied catchments and eight new catchments. These catchments belong to five previously studied catchment systems and one new catchment system (Tonlesap) in the Lower Mekong Basin. Two new catchment systems, Prachin Buri and Bang Pakong from eastern and central Thailand, respectively, were also examined. We collected 289 specimens of B. s. goniomphalos from 15 previously studied localities and 18 new localities in Thailand, Lao PDR (People's Democratic Republic), and Cambodia. The mitochondrial cytochrome c oxidase subunit 1 and 16S ribosomal DNA sequences were used to determine genetic variation. Classification of haplotypes specified 100 at the cox1 locus and 15 at the rrnL locus. Comparison between 16 catchment populations found significant genetic differences (Ф_ST) between all populations. The phylogenetic tree and haplotype network analyses classified B. s. goniomphalos into three evolutionary lineages (lineage I-III). Lineage I contained B. s. goniomphalos from the Mekong, Chi, Mun, Prachin Buri and Bang Pakong catchments in Thailand, including the Nam Ngum catchment in Lao PDR. Lineage II contained all specimens from the Tonlesap catchment, whereas lineage III contained specimens from the Mekong and Sea Bang Heang catchments in Thailand and Lao PDR, respectively. Interestingly, Bithynia siamensis siamensis was placed between lineages I and II of B. s. goniomphalos. This study supports the hypothesis that B. s. goniomphalos is a species complex containing at least three distinct evolutionary lineages in the Lower Mekong Basin, and that comprehensive molecular genetic analyses need to be conducted to further our understanding of the evolutionary and systematic relationships of these Bithynia snail taxa.

Multi-disciplinary integration of networking through the RNAS+: Research on other target diseases

In 2005, the network decided to increase its number of target diseases to include other helminthic zoonoses such as fascioliasis, clonorchiasis, opisthorchiasis, paragonimiasis and cysticercosis and in the process expanding membership to include South Korea, Vietnam, Thailand and Japan. NTDs were eventually included as awareness is heightened on these diseases affecting poor and developing countries. Researches on clonorchiasis and opisthorchiasis unravel the mechanism by which these diseases eventually predispose to cholangiocarcinoma. The liver cancer associated with these liver fluke infections necessitate the need to clarify the global burden of disease of these infections. The magnitude of these liver fluke diseases in endemic countries like China, Vietnam, Laos, Cambodia and Thailand is described. Success in elimination of lymphatic filariasis in PR China and Cambodia is highlighted to show how intensified multisectoral collaboration and strong political become strong ingredients in elimination of parasitic diseases like LF. New advances are presented that clarify species and strain differences in Fasciola spp., Paragonimus spp., Taenia spp. and Echinococcocus spp. Conventional diagnostic techniques are compared with new serologic techniques that are being developed. New control strategies such as the Lawa model are presented.

From country control programmes to translational research

From the time it was conceptualized in 1998 to the present, RNAS⁺ has largely concentrated on research that will generate results to facilitate control, prevention and elimination of its target diseases. Diagnostics has remained an active field of research in order to develop tools that are appropriate for each stage from the first efforts until attempts to block transmission. For example, with regard to schistosomiasis, chemotherapy has excellent impact on morbidity, while better diagnostics and vaccine research have been promoted to complement the other components of the control programme. The need for surveillance in areas where the prevalence has been brought down to very low levels necessitated development of spatio-temporal tools and ecological models based on geographical information systems (GIS) to produce risk and distribution maps for monitoring and evaluation of programme success. New knowledge and experiences in management of the diseases contribute to the formulation of new schemes in management and treatment. Ways of drawing attention to the disease, such as determining disability weights for use in computation of burden of disease, updating epidemiological profile and unravelling new aspects of the disease provide bases for modifying the operation of control programmes as we move forward. Programme evaluation based on reports of actual implementation of activities brought to the fore problems related to the distribution of chemotherapy as well as social, cultural and behavioural aspects of endemic communities. Importantly, this highlighted the necessity of adapting control activities to specific situations of the endemic areas. New models evolving from reviews of this kind and success stories, such us the elimination of lymphatic filariasis (LF) in PR China and Cambodia are presented.

A comprehensive review of omics and host-parasite interplays studies, towards control of Opisthorchis viverrini infection for prevention of cholangiocarcinoma

Opisthorchis viverrini infection, opisthorchiasis, is a food-borne trematodiasis that is the main cause of cholangiocarcinoma, a bile duct cancer, in the Lower Mekong sub-region of Lao PDR, Cambodia, Vietnam, and Thailand. Despite extensive research on opisthorchiasis, the eradication of this disease has yet to be achieved. One of the major reasons for this failure is due to the multi-host life cycle of the parasite, which requires complex medical and public health interventions to eradicate. Another reason is due to a lack of knowledge of not only the interactions between the parasite and the human immune system, but also the interactions between the parasite and its various hosts during its complicated life cycle. Recent advances in various high-throughput omics technologies has allowed for the identification of key biomolecules crucial to the processes of parasitic transmission, and the identification of novel drug and/or vaccine targets. In this paper, omics studies dealing with O. viverrini host-parasite biology will be reviewed. In particular, there will be a focus on the strategies O. viverrini uses to trigger, evade, and manipulate the host's defense systems. Recently-identified biological molecules with potential as targets for interventions will also be reviewed. The results obtained from these omics approaches to analyzing O. viverrini and host interactions will be of great importance in the future when developing effective and sustainable medical and public health models for the prevention and control of opisthorchiasis and opisthorchiasis-induced CCA.

Is Opisthorchis viverrini Emerging in Cambodia?

Opisthorchis viverrini infection is widely prevalent in Southeast Asia. In Cambodia information on this helminth infection is scare. Recent reports suggest that O. viverrini is an emerging public health problem. We aimed to synthesize all information in relation to the infection, epidemiology, and morbidity of O. viverrini in Cambodia; from published as well as thus far unpublished sources. First reports on O. viverrini date back to 1995. In 2006 an O. viverrini initiative was launched by the national helminth control program. Since then O. viverrini has been reported in all - except two - provinces. Villages with high prevalences (>20%) were found in provinces from Preah Vihear to Takeo. The infection has a highly focal distribution. In many villages no infections were detected. O. viverrini infection was also reported in cats, dogs and intermediate hosts. No report on morbidity associated with O. viverrini was found. The current evidence suggests that O. viverrini infection remains underreported in Cambodia. It is likely that the transmission will further increase in the future with potentially serious consequences for human health.

Liver Flukes: Clonorchis and Opisthorchis

Clonorchis sinensis, Opisthorchis viverrini, and O. felineus are liver flukes of human and animal pathogens occurring across much of Europe and Asia. Nevertheless, they are often underestimated compared to other, better known neglected diseases in spite of the fact that many millions of people are infected and hundreds of millions are at risk. This is possibly because of the chronic nature of the infection and disease and that it takes several decades prior to a life-threatening pathology to develop. Several studies in the past decade have provided more information on the molecular biology of the liver flukes which clearly lead to better understanding of parasite biology, systematics, and population genetics. Clonorchiasis and opisthorchiasis are characterized by a chronic infection that induces hepatobiliary inflammation, especially periductal fibrosis, which can be detected by ultrasonography. These chronic inflammations eventually lead to cholangiocarcinoma (CCA), a usually fatal bile duct cancer that develops in some infected individuals. In Thailand alone, opisthorchiasis-associated CCA kills up to 20,000 people every year and is therefore of substantial public health importance. Its socioeconomic impacts on impoverished families and communities are considerable. To reduce hepatobiliary morbidity and CCA, the primary intervention measures focus on control and elimination of the liver fluke. Accurate diagnosis of liver fluke infections in both human and other mammalian, snail and fish intermediate hosts, are important for achieving these goals. While the short-term goal of liver fluke control can be achieved by praziquantel chemotherapy, a comprehensive health education package targeting school children is believed to be more beneficial for a long-term goal/solution. It is recommended that a transdisciplinary research or multisectoral control approach including one health and/or eco health intervention strategy should be applied to combat the liver flukes, and hence contribute to reduction of cholangiocarcinoma in endemic areas.

Cholangiocarcinoma: a guide for the nonspecialist

Cholangiocarcinoma (CCA) is a tumor with increasing prevalence around the world. The prevalence of CCA is highest in East Asia and most significantly in the countries through which the Mekong River flows, owing to the presence of liver flukes, which are consumed in raw fish dishes. Outside Asia, the causes of bile duct cancers for the most part are unknown. In this review, we assess the current state of knowledge in both fluke-associated and sporadic CCA, from etiological, diagnostic, and treatment perspectives.

Human liver fluke Opisthorchis viverrini (Trematoda, Opisthorchiidae) in Central Myanmar: New records of adults and metacercariae identified by morphology and molecular analysis

Opisthorchis-like metacercariae were found in cyprinoid fish, Puntius brevis, bought from markets in the Bago region, Central Myanmar. Adult worms recovered from experimentally-infected hamsters resembled Opisthorchis viverrini. DNA was extracted from adults and metacercariae. A portion of the mitochondrial cytochrome c oxidase subunit 1 (cox1) and the internal transcribed spacer 2 (ITS2) regions were amplified using the polymerase chain reaction and then sequenced. The sequences confirmed that the flukes were O. viverrini. In phylogenetic analyses, sequences of O. viverrini, including our new sequences, clustered in a group with high bootstrap support for ITS2 (80%) and the cox1 gene (99%). Interestingly, ITS2 and cox1 sequences of O. viverrini and O. lobatus were very similar, raising a question about the identity of the latter. This is the first report of O. viverrini in cyprinoid fish in Central Myanmar, and only the second report of the species in Myanmar. It is an urgent warning against consuming raw or semi-cooked freshwater fish dishes. Development of an effective food-safety strategy should be provided for the prevention and control of opisthorchiasis and other foodborne diseases.

Active screening of gastrointestinal helminth infection in migrant workers in Thailand

Objective

This study aimed to detect gastrointestinal helminth infection in migrant workers in Thailand.

Methods

A cross-sectional survey study was conducted in 403 migrant workers in the factories of Nakhon Ratchasima Province, northeastern Thailand during October 2016 to June 2017. Gastrointestinal helminth infections were detected by the formalin ether acetate concentration technique and microscopy. The data were analyzed using the χ²-test and logistic regression.

Results

The rate of gastrointestinal helminth infection was 24.07%. The most common species involved in infection was Opisthorchis viverrini (11.91%), followed by hookworm (5.46%), Trichuris trichiura (5.21%), Strongyloides stercoralis (0.5%), Ascaris lumbricoides (0.5%), and Taenia spp. (0.5%). The majority of infections were found in men aged ≥40 years, married participants, uneducated participants, laborers, those who worked for 1 year, and those who had an income of 9000 to 12,000 THB.

Conclusions

Gastrointestinal helminth infection is still found in migrant workers. Therefore, active surveillance is required in this large group for investigating and eradicating this type of infection.

Common Illnesses in Tropical Asia and Significance of Medical Volunteering

This study was conducted to provide practical information for actual preparation of medical volunteering in tropical Asia, mainly the distribution of common illnesses encountered during mission. From 2012 to 2017, we visited two rural areas of Eastern Cambodia for medical volunteering missions, Cham Lak and Khsoem. Neither area has electricity or public water. We classified the common cases encountered during missions into six groups (upper respiratory infection, gastroenteritis, vaginitis and/or cystitis, dermatitis, work-related pain and parasite prevention) and assessed the distribution. In Cham Lak and Khsoem, 558 and 371 people were treated, respectively. The most commonly encountered cases in children under age of 18 were upper respiratory infection, followed by parasite control and dermatitis, in both areas. There was no significant difference in distribution between the two areas. For adults, the most common illnesses in Cham Lak area were vaginitis and/or cystitis, followed by gastroenteritis and work-related pain. In Khsoem area, the common illnesses were work-related pain followed by gastroenteritis, and upper respiratory infection. The distribution between the two areas differed significantly (p <0.001). The difference might be due to the water source and main crops of agriculture. Successful preparation of a medical volunteering needs deep understanding of the destination community.

Snail-borne parasitic diseases: an update on global epidemiological distribution, transmission interruption and control methods

Background

Snail-borne parasitic diseases, such as angiostrongyliasis, clonorchiasis, fascioliasis, fasciolopsiasis, opisthorchiasis, paragonimiasis and schistosomiasis, pose risks to human health and cause major socioeconomic problems in many tropical and sub-tropical countries. In this review we summarize the core roles of snails in the life cycles of the parasites they host, their clinical manifestations and disease distributions, as well as snail control methods.

Main body

Snails have four roles in the life cycles of the parasites they host: as an intermediate host infected by the first-stage larvae, as the only intermediate host infected by miracidia, as the first intermediate host that ingests the parasite eggs are ingested, and as the first intermediate host penetrated by miracidia with or without the second intermediate host being an aquatic animal. Snail-borne parasitic diseases target many organs, such as the lungs, liver, biliary tract, intestines, brain and kidneys, leading to overactive immune responses, cancers, organ failure, infertility and even death. Developing countries in Africa, Asia and Latin America have the highest incidences of these diseases, while some endemic parasites have developed into worldwide epidemics through the global spread of snails. Physical, chemical and biological methods have been introduced to control the host snail populations to prevent disease.

Conclusions

In this review, we summarize the roles of snails in the life cycles of the parasites they host, the worldwide distribution of parasite-transmitting snails, the epidemiology and pathogenesis of snail-transmitted parasitic diseases, and the existing snail control measures, which will contribute to further understanding the snail-parasite relationship and new strategies for controlling snail-borne parasitic diseases.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0414-7) contains supplementary material, which is available to authorized users.

Epidemiology of Opisthorchis viverrini Infection

Opisthorchiasis in the Lower Mekong Subregion is a parasitic disease caused by the liver fluke Opisthorchis viverrini. This parasite has a well-documented distribution in Thailand, Lao PDR, Cambodia, Myanmar and Southern Vietnam. In this chapter, we describe the current knowledge of the epidemiology of O. viverrini infection, highlighting advances in control efforts made in the last four decades in Thailand and identifying ongoing gaps in our epidemiological knowledge which need to be filled to support efforts to permanently overcome the heavy morbidity and mortality burden caused by these parasites within their endemic regions.

Chicken IgY-based coproantigen capture ELISA for diagnosis of human opisthorchiasis

Diagnosis of Opisthorchis viverrini infection by conventional stool examination is increasingly difficult due to the low intensity of the infection after several rounds of control programmes in endemic regions as well as coinfections with intestinal flukes. Therefore sensitive and specific diagnostic test is needed. In this study, a coproantigen sandwich ELISA using recombinant O. viverrini cathepsin F (rOv-CF) was developed. This sandwich ELISA employing chicken IgY raised against rOv-CF in combination with rabbit IgG antibody to the somatic O. viverrini antigens showed a lower detection limit (LLD) of 70ng native O. viverrini somatic antigens by spiking the parasite antigens into control feces. When applied to the diagnosis, the IgY-based sandwich ELISA exhibited sensitivity and specificity of 93.3% and 76.7%, respectively, in an investigation of 90 human cases positive or negative for opisthorchiasis. The positive predictive value (PPV) and negative predictive value (NPV) for this coproantigen detection were 66.7% and 95.2%, respectively. This IgY-based sandwich ELISA using parasite cathepsin F detection shows a promising immunodiagnostic alternative for human opisthorchiasis in endemic regions.

The role of domestic dogs in the transmission of zoonotic helminthes in a rural area of Mekong river basin

Dogs have been bred since ancient times for companionship, hunting, protection, shepherding and other human activities. Some canine helminth parasites can cause significant clinical diseases in humans as Opisthorchis viverrini causing cholangiocarcinoma in Southeast Asian Countries. In this study, socio-cultural questionnaire, canine parasitological analysis, necropsy, parasite molecular confirmation and dog roaming data were evaluated in Savannakhet, Lao-PDR, a typical Mekong Basin area. Dog owners comprised 48.8% of the studied population, with 61.2% owning one dog, 25.1% 2 dogs, 8.5% 3 dogs and 1.8% owning more than 4 dogs. Data from GPS logger attached to dogs showed they walked from 1.4 to 13.3 km per day, covering an area of 3356.38m2 average, with a routine of accessing water sources. Thirteen zoonotic helminth species were observed. Causative agents of visceral and cutaneous larva migrans occurred in 44.1% and 70% of the samples respectively. Spirometra erinaceieuropaei was detected in 44.1% of samples. Importantly, O. viverrini was found in 8.8% of samples. Besides the known importance of dogs in the transmission of Ancylostoma spp., Toxocara spp. and S. erinaceieuropaei, the observed roaming pattern of dogs confirmed it as an important host perpetuating O. viverrini in endemic areas; their routine access to waterbodies may spread O. viverrini eggs in a favorable environment for the fluke development, facilitating the infection of fishes, and consequently infecting humans living in the same ecosystem. Therefore, parasitic NTDs control programs in humans should be done in parallel with parasite control in animals, especially dogs, in the Mekong River basin area.

First report and molecular identification of Opisthorchis viverrini infection in human communities from Lower Myanmar

Opisthorchis viverrini is endemic in the South East Asian region, especially in Cambodia, Lao People's Democratic Republic, Vietnam and Thailand, but there have been no previous records from Myanmar. During stool surveys of rural populations in three regions of Lower Myanmar, Opisthorchis-like eggs were found in 34 out of 364 (9.3%) participants by stool microscopy after using the modified formalin-ether concentration technique. DNA was extracted from these positive stool samples and a portion of the mitochondrial cytochrome c oxidase subunit I (cox1) gene was amplified using the polymerase chain reaction and then sequenced. DNA sequences, successfully obtained from 18 of 34 positive samples (Bago Region, n = 13; Mon State, n = 3; Yangon Region, n = 2), confirmed that the eggs were of O. viverrini. Sequences showed 99.7% identity with O. viverrini mitochondrial cox1 (GenBank accession no. JF739555) but 95%, 88.7%, 82.6% and 81.4% identities with those of Opisthorchis lobatus from Lao People's Democratic Republic (GenBank accession nos. HQ328539-HQ328541), Metorchis orientalis from China (KT239342), Clonorchis sinensis from China (JF729303) and Opisthorchis felineus from Russia (EU921260), respectively. When alignement with other Opisthorchiidae trematodes, 81% similarity with Metorchis bilis from Czech Republic (GenBank accession nos. KT740966, KT740969, KT740970) and Slovakia (GenBank accession nos. KT740971-KT740973), 84.6% similarity with Metorchis xanthosomus from Czech Republic (GenBank accession no. KT740974), 78.6% similarity with M. xanthosomus from Poland (GenBank accession no. KT740968) and 82.2% similarity with Euamphimerus pancreaticus from Czech Republic (GenBank accession no. KT740975) were revealed. This study demonstrated, for the first time, O. viverrini from rural people in Myanmar using molecular methods and is an urgent call for surveillance and control activities against opisthorchiasis in Myanmar.

Prevalence and Factors Associated with Opisthorchis viverrini Infection in Khammouane Province, Lao PDR

Opisthorchis viverrini (OV) liver flukes are common parasites found in central and southern Laos and constitute a major public health problem in the country. Laos people continue to have the habit of extensively consuming raw or half-cooked fish which are intermediate hosts. This study aimed to study the prevalence and factors associated with OV infection in the population of Thakek district, Khammouane Province. This cross-sectional analytic study covered 237 subjects who filled out structured questionnaires. Fecal examination for OV infection was performed by Kato's thick smear method. Data analysis was carried out using STATA Version 10.0. Multiple logistic regression was applied. The results showed that the infection rate of OV was 54.8 %. Factors associated with OV infections were gender, a habit of defecation in fields and raw fish (goi bplaa dip) consumption. Opisthorchiasis and associated cholangiocarcinoma development thus appear to remain as important concerns in Laos.

Clonorchis sinensis and Opisthorchis spp. in Vietnam: current status and prospects

Clonorchis sinensis and Opisthorchis viverrini are clinically important small liver flukes because of their known association with development of cholangiocarcinoma. In Vietnam, high prevalence of C. sinensis infection in humans was previously reported in northern provinces, and O. viverrini infection has been detected in several central provinces. However, diagnosis of C. sinensis and O. viverrini infections in the past was merely based on faecal egg examination. This method alone can lead to misidentification at the species level because of morphological similarity between the eggs of these liver flukes and minute intestinal trematodes of the family Heterophyidae. In fact, recent surveys in Vietnam revealed that infection with several minute intestinal flukes, such as Haplorchis pumilio and H. taichui, are much more common than infection with C. sinensis or O. viverrini, and they often co-infect humans. Thus, previously reported prevalence of small liver fluke infection in Vietnam was likely over-estimated due to mis identification of parasites in copro-parasitological examinations. In addition, there is some confusion about identification of cercariae, metacercariae and also adults of C. sinensis and O. viverrini in intermediate and definitive hosts. The aim of this review is, therefore, to draw realistic pictures of the past and present scientific reports on the epidemiology and biology of C. sinensis and Opisthorchis spp. infection in Vietnam.

A 13-Year Retrospective Study on Primary Liver Cancer in Cambodia: A Strikingly High Hepatitis C Occurrence among Hepatocellular Carcinoma Cases

OBJECTIVES

Hepatocellular carcinoma (HCC) is the main type of primary liver cancer (PLC) worldwide, but cholangiocarcinoma (CCA) may be predominant in some specific regions of Southeast Asia. The aim of the present study was to delineate a pattern of Cambodian PLC patients attending the Calmette Hospital in the Cambodian capital Phnom Penh.

MATERIALS AND METHODS

A total of 553 medical charts diagnosing PLCs from January 2003 to May 2015 were obtained from both the Oncology and Hepato-Gastroenterology Departments of the Calmette Hospital.

RESULTS

HCC was the predominant type of PLC recorded, with 511 cases (92.4%), whereas CCA represented merely 7.6% (42 cases) of the overall series. Hepatitis B virus (HBV; 44.3%) and hepatitis C virus (HCV; 43%) infection rates were similar among the HCC patients, while small subsets of CCA patients were infected with HBV (15.4%) or HCV (11.5%). Most HCC (84%) and CCA (73.8%) patients received palliative treatment only.

CONCLUSION

The present study indicates that HCC is the main form of primary hepatic neoplasm among PLC patients attending a hospital in Cambodia. HBV and HCV infections represented equivalent burdens and major contributing factors to HCC. Therefore, the implementation of prevention programs for these infectious agents should become a priority for health policy makers in the country.

Immunodiagnosis of opisthorchiasis using parasite cathepsin F

Opisthorchis viverrini, a food-borne trematode parasite endemic in the lower Mekong countries, is conventionally diagnosed by stool examination. However, parasitological stool-based diagnosis can be unreliable in light infections. The goal of this study was to develop the immunodiagnosis of opisthorchiasis using cathepsin F cysteine protease of O. viverrini in both indirect and sandwich ELISA assays. A recombinant O. viverrini cathepsin F (rOv-CF) of 40 kDa was expressed in E. coli strain BL21 (DE3), affinity purified, and deployed in ELISA assays. Human sera from 272 cases were investigated by indirect rOv-CF-based ELISA. Positive antibody response to rOv-CF was found in 137 out of 272 cases (50.37 %) using a cutoff OD (0.400) determined by ROC analysis. In comparison to parasitological stool examined for fluke eggs, the gold standard, the rOv-CF indirect ELISA showed a sensitivity and specificity of 62.1 and 84.05 %, respectively. Serum antibody levels correlated well with egg counts per gram feces (EPG) (P < 0.001). In addition, chicken IgY antibody raised against rOv-CF was tested in a sandwich ELISA for detection of coproantigen in the feces of experimentally infected hamsters. The sandwich ELISA using this chicken IgY in combination with rabbit antibody to O. viverrini somatic antigens showed sensitivity and specificity of 93.3 and 78.57 %, respectively. Together, these findings indicated the potential of rOv-CF for diagnosis of opisthorchiasis, including for uses with chicken IgY for detection of coproantigens of O. viverrini.

Intestinal parasite infections in symptomatic children attending hospital in Siem Reap, Cambodia

BACKGROUND

Infections with helminths and other intestinal parasites are an important but neglected problem in children in developing countries. Accurate surveys of intestinal parasites in children inform empirical treatment regimens and can assess the impact of school based drug treatment programmes. There is limited information on this topic in Cambodia.

METHODS

In a prospective study of intestinal parasites in symptomatic children attending Angkor Hospital for Children, Siem Reap, Cambodia, April-June 2012, samples were examined by microscopy of a direct and concentrated fecal sample. Two culture methods for hookworm and Strongyloides stercoralis were employed when sufficient sample was received. Demographic, clinical and epidemiological data were collected.

PRINCIPAL FINDINGS

We studied 970 samples from 865 children. The median (inter-quartile range) age of the children was 5.4 (1.9-9.2) years, 54% were male. The proportion of children with abdominal pain was 66.8%, diarrhea 34.9%, anemia 12.7% and malnutrition 7.4%. 458 parasitic infections were detected in 340 (39.3%) children. The most common parasites using all methods of detection were hookworm (14.3%), Strongyloides stercoralis (11.6%) and Giardia lamblia (11.2%). Giardia lamblia was most common in children aged 1-5 years, hookworm and Strongyloides stercoralis were more common with increasing age. Hookworm, Strongloides stercoralis and Giardia lamblia were more common in children living outside of Siem Reap town. In a multivariate logistic regression increasing age was associated with all three infections, defecating in the forest for hookworm infection, the presence of cattle for S. stercoralis and not using soap for handwashing for G. lamblia.

CONCLUSIONS/SIGNIFICANCE

This study confirms the importance of intestinal parasitic infections in symptomatic Cambodian children and the need for adequate facilities for laboratory diagnosis together with education to improve personal hygiene and sanitation.

Prevalence of intestinal helminths among inhabitants of Cambodia (2006-2011)

In order to investigate the status of intestinal helminthic infections in Cambodia, epidemiological surveys were carried out on a national scale, including 19 provinces. A total of 32,201 fecal samples were collected from schoolchildren and adults between 2006 and 2011 and examined once by the Kato-Katz thick smear technique. The overall egg positive rate of intestinal helminths was 26.2%. The prevalence of hookworms was the highest (9.6%), followed by that of Opisthorchis viverrini/minute intestinal flukes (Ov/MIF) (5.7%), Ascaris lumbricoides (4.6%), and Trichuris trichiura (4.1%). Other types of parasites detected were Enterobius vermicularis (1.1%), Taenia spp. (0.4%), and Hymenolepis spp. (0.2%). The northwestern regions such as the Siem Reap, Oddar Meanchey, and Banteay Meanchey Provinces showed higher prevalences (17.4-22.3%) of hookworms than the other localities. The southwestern areas, including Koh Kong and Preah Sihanouk Provinces showed higher prevalences of A. lumbricoides (17.5-19.2%) and T. trichiura (6.1-21.0%). Meanwhile, the central and southern areas, in particular, Takeo and Kampong Cham Provinces, showed high prevalences of Ov/MIF (23.8-24.0%). The results indicate that a considerably high prevalence of intestinal helminths has been revealed in Cambodia, and thus sustained national parasite control projects are necessary to reduce morbidity due to parasitic infections in Cambodia.