Helminth infection in southern Laos: high prevalence and low awareness

Prevalence estimates of Opisthorchis viverrini and Clonorchis sinensis infection in the Greater Mekong subregion: a systematic review and meta-analysis

BACKGROUND

Opisthorchiasis and clonorchiasis, caused by Opisthorchis viverrini and Clonorchis sinensis, respectively, are significant yet neglected foodborne trematodiases in the Great Mekong Subregion (GMS). Despite the reporting of the prevalence of these human liver flukes in the region over the past decades, there has been a lack of a comprehensive and systematic consolidation of this data. Therefore, we aimed to conduct a thorough systematic review and meta-analysis to synthesize and analyze time-trend prevalence estimates of both O. viverrini and C. sinensis across the GMS for the past 30 years.

METHODS

This study undertakes a systematic review using a comprehensive search for published articles in PubMed, EMBASE, Scopus, Cochrane and Thai Journal Online databases until early 2023. The pooled prevalence of O. viverrini and C. sinensis infection was analyzed through a random-effects meta-analysis, with meta-regression analysis used to quantify associations with study characteristics. Sub-group analysis was conducted, whenever comparison data were available, to assess the risk of O. viverrini and C. sinensis infection in each GMS country. Heterogeneity among studies was assessed using the Q statistic and quantified by using the I 2 Index.

RESULTS

From a total of 2997 articles, 155 articles comprising 218 datasets and 751,108 participants were included for review. The GMS prevalence of O. viverrini was 21.11% [45,083/260,237; 95% confidence interval (CI): 17.74-24.47%]. Pooled prevalence estimates were highly observed in Laos (34.06%, 95% CI: 26.85-41.26%), followed by Thailand (18.19%, 95% CI: 13.86-22.51%), and Cambodia (10.48%, 95% CI: 5.52-15.45%). Myanmar and Vietnam had limited data sources for calculation. Clonorchis sinensis infection in GMS was 25.33% (95% CI: 18.32-32.34%), with Guangxi, China, exhibiting the highest prevalence rates at 26.89% (95% CI: 18.34-35.43%), while Vietnam had a prevalence rate of 20.30% (95% CI: 9.13-31.47%). O. viverrini prevalence decreased significantly over time, whereas C. sinensis infection appeared to be stable consistently over time in both China and Vietnam.

CONCLUSIONS

This comprehensive study, drawing from the largest datasets to date, offers an in-depth systematic prevalence review of human liver flukes in the Greater Mekong Subregion. It underscores the imperative for systematic surveillance, data collection, and the implementation of intervention and control measures for these infectious diseases of poverty.

A Socio-Ecological Framework for Examining Foodborne Parasitic Infection Risk

Human liver fluke infection through the consumption of raw freshwater fish is one of the foodborne parasitic infections of global concern. Despite decades of health campaign efforts, high prevalence of infection remains in different areas of the Lower Mekong Basin. This necessitates the consideration of the infection differences between places and the human-environment complexities of disease transmission. This paper used the socio-ecological model as a framework to unraveled the social science dimensions of liver fluke infection. We conducted questionnaire surveys in Northeast Thailand to gather participants' knowledge on liver fluke infection and reasons for raw fish consumption. We synthesized our findings with prior work to identify factors influencing liver fluke infection at four socio-ecological levels. At the individual level, gender and age differences in food consumption habits and personal hygiene of open defection presented the behavioral risks. At the interpersonal level, family tradition and social gathering affected the disease risk. At the community level, physical-social-economic environments of land use and modernization, community health infrastructure and health volunteer support accounted for the varying degree of infection. At the policy level, impacts of regional and national regulations on disease control, health system organization structure, and government development projects were of concerned. The findings provide insights into how infection risks are shaped by people's behavior, social connectedness, interactions with places, and the interplay of these multi-level socio-ecological influences. The framework therefore allows a more comprehensive understanding of liver fluke infection risks to inform a culturally sensitive and sustainable disease control program.

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.

Epidemiology and Control of Opisthorchis viverrini Infection: Implications for Cholangiocarcinoma Prevention

It is known that Opisthorchis viverrini (OV) is the most significant risk factor for the development of cholangiocarcinoma (CCA); hence, it is also known as carcinogenic parasite. Effective control and elimination of OV infection should significantly reduce O. viverrini-related CCA. This chapter includes details of the three recently developed innovative tools, namely the Isan cohort database software, an OV-RDT for screening of O. viverrini, and an ultrasound telecommunication system. Past and current control programs, i.e., education, medication, and sanitation were discussed and stressed the need for a comprehensive control program which encompasses primary, secondary, and tertiary patient care programs for confirmation and management of suspected CCA cases. The approach of mathematical modeling for control of OV and CCA was also briefly described. Additionally, we highlighted the current progress toward control of OV and CCA in Thailand and potential for expansion into nearby countries in Southeast Asia.

Effectiveness of public health interventions in reducing the prevalence of Opisthorchis viverrini: a protocol for systematic review and network meta-analysis

INTRODUCTION

The carcinogenic liver fluke Opisthorchis viverrini is a major public health problem in the Mekong basin region. The liver flukes can induce cholangiocarcinoma, a bile duct cancer that causes a significant burden of mortality and economic loss. Various public health interventions have been conducted to reduce opisthorchiasis but the prevalence of O. viverrini remains high in endemic regions. The aim is to quantify the effectiveness of public health interventions in reducing the prevalence of O. viverrini infection.

METHODS AND ANALYSIS

Seven databases (including PubMed, SCOPUS, Web of Science, EMBASE, ScienceDirect, Thai thesis database and TCI (Thai journals online)) will be searched from initiation through to 2022 to identify studies of interventions to reduce the prevalence of O. viverrini infection. The prevalence, incidence or number of O. viverrini-infected people will be used as the source of O. viverrini prevalence data. A conventional meta-analysis and a Bayesian network meta-analysis will be conducted to undertake direct and indirect comparisons of different interventions. Meta-regression will be used to determine the effect of each intervention. The risk of bias will be assessed using the Cochrane Collaboration's risk of bias tool. Heterogeneity between studies will be determined by forest plots and I2 and publication bias investigated with funnel plots and the Egger's test.

ETHICS AND DISSEMINATION

Ethical approval will not be required because this study will only use published data. The final report of this review will be disseminated through publication in a peer-reviewed scientific journal and will also be presented at relevant conferences.

PROSPERO REGISTRATION NUMBER

CRD42022323066.

Stunting as a Risk Factor of Soil-Transmitted Helminthiasis in Children: A Literature Review

As a high-burden neglected tropical disease, soil-transmitted helminth (STH) infections remain a major problem in the world, especially among children under five years of age. Since young children are at high risk of being infected, STH infection can have a long-term negative impact on their life, including impaired growth and development. Stunting, a form of malnutrition in young children, has been long assumed as one of the risk factors in acquiring the STH infections. However, the studies on STH infection in children under five with stunting have been lacking, resulting in poor identification of the risk. Accordingly, we collected and reviewed existing related research articles to provide an overview of STH infection in a susceptible population of stunted children under five years of age in terms of prevalence and risk factors. There were 17 studies included in this review related to infection with Ascaris lumbricoides, Trichuris trichiura, hookworm, and Strongyloides stercoralis from various countries. The prevalence of STH infection in stunted children ranged from 12.5% to 56.5%. Increased inflammatory markers and intestinal microbiota dysbiosis might have increased the intensity of STH infection in stunted children that caused impairment in the immune system. While the age from 2 to 5 years along with poor hygiene and sanitation has shown to be the most common risk factors of STH infections in stunted children; currently there are no studies that show direct results of stunting as a risk factor for STH infection. While stunting itself may affect the pathogenesis of STH infection, further research on stunting as a risk factor for STH infection is encouraged.

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 of Opisthorchis viverrini and Its Associated Risk Factors in the Phon Sawan District of Nakhon Phanom Province, Thailand

Background:

Opisthorchis viverrini is one of the endemic helminths in Thailand. Nonetheless, O. viverrini still exist and raise concerns regarding public health. This study aimed to evaluate the current prevalence of O. viverrini infections and underlying risk factors among rural communities in Northeast Thailand.

Methods:

A cross-sectional study was conducted between Sep and Dec 2019 in Phon Sawan district in Nakhon Phanom Province, Thailand. The participants were selected using a voluntary sampling method after the proportional allocation of the total sample size. Demographic data were collected using a standardized questionnaire. One stool sample was collected from each participant and the presence of O. viverrini and other intestinal parasite infections were determined using the modified Kato-Katz technique.

Results:

Overall, 250 participants aged 21 yr or older were enrolled. Overall, the prevalence of O. viverrini and Strongyloides stercoralis was 24% (95% confidence interval [CI]: 18.8–29.8) and 1.2% (95% CI: 0.2–3.5), respectively. Of the positive O. viverrini cases, the parasite rate significantly differed between gender, age group and in those who had a history of eating raw fish and taking the anti-helminthic drug (all P<0.05). Nevertheless, multivariate regression analysis among O. viverrini cases revealed that only being male (adjusted odds ratio [aOR] 1.9 [95% CI: 1.1 – 3.6], P = 0.033) and aged ≥61 yr (aOR 6.7 [95% CI: 1.4 – 32.5], P=0.018) were positively associated with a higher risk of O. viverrini infection.

Conclusion:

Opisthorchiasis and strongyloidiasis are still endemic in this area and there is a need for projects to eliminate these parasites.

Cluster of Angiostrongyliasis Cases Following Consumption of Raw Monitor Lizard in the Lao People's Democratic Republic and Review of the Literature

Angiostrongyliasis in humans causes a range of symptoms from mild headache and myalgia to neurological complications, coma and death. Infection is caused by the consumption of raw or undercooked intermediate or paratenic hosts infected with Angiostrongylus cantonensis or via contaminated vegetables or water. We describe a cluster of cases involved in the shared meal of wild raw monitor lizard in the Lao PDR. Seven males, aged 22–36 years, reported headaches, abdominal pain, arthralgia, myalgia, nausea/vomiting, diarrhea, neurological effects and loss of appetite. Five were admitted to hospital. The final diagnosis was made by clinical presentation and case history, and positive A. cantonensis PCR for two cases. All hospitalized patients recovered fully following supportive treatment. The remaining two individuals sought local home remedies and made full recovery. Whilst most published reports concern infections via consumption of molluscs, few detailed reports exist on infections that result from the consumption of reptiles and there exists little awareness in Lao PDR. This case cluster, which originates from a single meal, highlights the potential public health risk of the consumption of raw and wild-caught meat in Lao PDR and the Southeast Asia region. Without specific diagnostics, clinical history and the consideration of recent food consumption are important when evaluating patients.

Insights into hookworm prevalence in Asia: a systematic review and meta-analysis

INTRODUCTION

Hookworm infections are neglected tropical diseases of humans and animals worldwide. A meta-analysis and systematic review was designed to evaluate the prevalence of hookworm infection in animal and human hosts in Asia until July 2018.

METHODS

The available online articles of five English databases (PubMed, Scopus, Science Direct, Web of Science and Google Scholar) were explored.

RESULTS

The most parasitized carnivores were jackal (48%, CI: 4 to 91%), followed by dog (41%, CI: 29 to 53%), cat (26%, CI: 14 to 38%) and the red fox (19%, CI: 13 to 24%). The weighted prevalence of Ancylostoma braziliensis, A. caninum, A. ceylanicum, A. tubaeforme and Uncinaria stenocephala isolated from different canids were found to be 27% (CI: 21 to 33%), 23% (CI: 7.0 to 53%), 24% (CI: 12 to 35%), 44% (CI: 37 to 51%) and 37% (CI: 18 to 55%), respectively. In total, 98 records were obtained for human hookworms from 3209 760 examined individuals and the calculated weighted prevalence in this population was 19% (CI: 17 to 20%).

CONCLUSIONS

These findings highlight a desirable ecological milieu for parasite survival and transmission in such territories, which implicates revisiting control programs and public health infrastructures in those areas.

Prevalence and Risk Factors of Intestinal Helminthiasis in Remote Mountainous Villages of Northern Lao PDR: A Cross-Sectional Study

Helminth infections are prevalent in Lao People’s Democratic Republic (Lao PDR). This study aimed at determining the prevalence and risk factors of intestinal helminthiasis in remote mountainous villages of northern Lao PDR. During the dry season in January 2017, a cross-sectional survey was conducted in 3 remote mountainous villages in Oudomxay province, Lao PDR. Villagers older than 18 years of age who agreed to submit stool samples or undergo an interview, were recruited. Stool samples from 198 individuals were examined by the Kato-Katz method, and a questionnaire surveyed 161 individuals among them. Univariable and multivariable logistic regression analyses were used to identify risk factors associated with the intestinal helminthiasis. An overall prevalence of intestinal helminthiasis was 75.8%. Hookworm infection was the most common (63.1%), followed by Opisthorchis viverrini/minute intestinal flukes (17.7%), Taenia spp. (15.2%), Trichuris trichiura (2.0%), Ascaris lumbricoides (1.5%), and Enterobius vermicularis (1.0%). Questionnaire analysis revealed sex (male) and absence of latrine to be significant risk factors for hookworm infection and consumption of raw meat for taeniasis. These results suggest that the mountainous area in northern Lao PDR has a different composition of helminth infections from other studies conducted in Lao PDR; a high prevalence of hookworm infection and taeniasis and low prevalence of T. trichiura and A. lumbricoides infections were observed. Also, liver flukes or intestinal flukes were similarly prevalent in the mountainous area.

Prevalence of anemia and its associated factors among children aged 6-59 months in the Lao People's Democratic Republic: A multilevel analysis

Anemia is a major public health concern among children aged <5 years in the Lao People’s Democratic Republic. Thus far, no study has determined the factors associated with anemia among children aged <5 years in the Lao People’s Democratic Republic using a nationwide representative sample. Therefore, this study aimed to evaluate the prevalence of anemia and its associated factors with multilevel variations among children aged 6–59 months. This quantitative, cross-sectional study used a nationally representative sample from the Lao Social Indicator Survey II, 2017. Children aged 6–59 months tested for anemia were included in this study through multistage sampling approaches. Anemia was defined as a hemoglobin level of <11.0 g/dL. Multilevel binary logistic regression analyses were used to determine the adjusted effect of the factors associated with anemia. Among the 5,087 children included, the overall prevalence of anemia was 43.0%. Three factors were associated with higher odds of developing anemia—male sex (adjusted odds ratio, 1.16; 95% confidence interval, 1.01–1.34), underweight (adjusted odds ratio, 1.30; 95% confidence interval, 1.09–1.55), and residence in central provinces (adjusted odds ratio, 1.59; 95% confidence interval, 1.30–1.95) and southern provinces (adjusted odds ratio, 1.42; 95% confidence interval, 1.11–1.81). However, the other three factors—age, educational level of the household head, and Hmong-Mien ethnicity—were inversely associated with anemia. To resolve the problem regarding the severity of the anemia among children aged <5 years in the Lao People’s Democratic Republic. Our findings highlight the need for designing an effective approach to address each factor associated with childhood anemia. Interventions should focus on the prevention of childhood anemia, which is considered a major priority of public health intervention in the Lao People’s Democratic Republic.

Prevalence of strongyloidiasis in the general population of the world: a systematic review and meta-analysis

Strongyloides stercoralis is a neglected soil-transmitted helminth affects approximately 100-370 million people globally. The life cycle is unusual as only larvae can be found in stool specimens. Thecurrent review and meta-analysis represented the distribution of strongyloidiasis in general population of the world based on published papers. Five English databases (Science Direct, Scopus, PubMed, Web of Science, and Google Scholar(were explored for literature published before October 2019.Altogether 235 studies (862243 participants) was eligible. Regarding diagnostic method, the overall prevalence for studies performed microscopic, culture, immunological and molecular method was 1.47% (95% CI = 1.56%), 10.08% (95% CI = 8.99% - 11.16%), 23.88% (95% CI =  20.82% - 26.94%) and 9.3% (95% CI  =  7.2% - 11.3%), respectively. Based on microscopic methods, the highest prevalence was related to the Western Pacific region [9.47% (95% CI =  8.55% - 10.39%)]. According to the culture method, Western Pacific region [21.36% (95% CI  =  16.32% - 26.39%)] had the highest estimated pooled prevalence. In immunological studies, Eastern Mediterranean Region [40.72% (95% CI  =  36.74% - 44.70%)] had the highest seroprevalence.Also in molecular surveys, the highest prevalence was related to the African region [19.72% (95% CI  =  16.71% - 22.73%)]. The current study indicated that strongyloidiasis is still considered a health problem in many parts of the world. Thus a comprehensive control program and improvement of public health sectors are required.

Zoonotic transmission of intestinal helminths in southeast Asia: Implications for control and elimination

Intestinal helminths are extremely widespread and highly prevalent infections of humans, particularly in rural and poor urban areas of low and middle-income countries. These parasites have chronic and often insidious effects on human health and child development including abdominal problems, anaemia, stunting and wasting. Certain animals play a fundamental role in the transmission of many intestinal helminths to humans. However, the contribution of zoonotic transmission to the overall burden of human intestinal helminth infection and the relative importance of different animal reservoirs remains incomplete. Moreover, control programmes and transmission models for intestinal helminths often do not consider the role of zoonotic reservoirs of infection. Such reservoirs will become increasingly important as control is scaled up and there is a move towards interruption and even elimination of parasite transmission. With a focus on southeast Asia, and the Philippines in particular, this review summarises the major zoonotic intestinal helminths, risk factors for infection and highlights knowledge gaps related to their epidemiology and transmission. Various methodologies are discussed, including parasite genomics, mathematical modelling and socio-economic analysis, that could be employed to improve understanding of intestinal helminth spread, reservoir attribution and the burden associated with infection, as well as assess effectiveness of interventions. For sustainable control and ultimately elimination of intestinal helminths, there is a need to move beyond scheduled mass deworming and to consider animal and environmental reservoirs. A One Health approach to control of intestinal helminths is proposed, integrating interventions targeting humans, animals and the environment, including improved access to water, hygiene and sanitation. This will require coordination and collaboration across different sectors to achieve best health outcomes for all.

Infection status with zoonotic trematode metacercariae in fish from Lao PDR

Studies on the infection status with fishborne zoonotic trematode (FZT) metacercariae were reviewed with our data, which obtained from the fish survey in 8 administrative localities, i.e., Vientiane Municipality, Luang Prabang, Xieng Khouang, Vientiane, Khammuane, Savannakhet, Saravane and Champasak Provinces of Lao PDR (Laos) in 10 times. Total 1046 freshwater fishes (69 species) were examined with the artificial digestion method from 2002 to 2011. Total 6 species of zoonotic trematode, i.e., Opisthorchis viverrini, Haplorchis taichui, Haplorchis yokogawai, Haplorchis pumilio, Centrocestus formosanus and Procerovum varium, metacercariae were detected in fishes from Laos. The metacercariae of O. viverrini were detected in 284 (37.9%) out of 749 fishes (26 spp.), and their average density was 297 per fish infected. The prevalences of 4 heterophyid species, i.e., H. taichui, H. yokogawai, H. pumilio and C. formosanus, metacercariae were 45.4% (out of 941 fishes in 46 spp. examined), 45.1% (811 fishes in 35 spp.), 8.8% (457 fishes in 11 spp.) and 18.1% (475 fishes in 13 spp.), their average densities were 291, 218, 4 and 15 per fish infected respectively. The endemicities of O. viverrini metacercariae were much higher in fishes from Savannakhet Province and Vientiane Municipality (2002). Those of H. taichui metacercariae were much higher in fishes from Khammuane and Luang Prabang (2011) Provinces. By the present study, it was confirmed that some species of FZT metacercariae are highly prevalent in fishes from Laos.

Bayesian spatial analysis of cholangiocarcinoma in Northeast Thailand

Cholangiocarcinoma (CCA) is a malignant neoplasm of the biliary tract. Thailand reports the highest incidence of CCA in the world. The aim of this study was to map the distribution of CCA and identify spatial disease clusters in Northeast Thailand. Individual-level data of patients with histopathologically confirmed CCA, aggregated at the sub-district level, were obtained from the Cholangiocarcinoma Screening and Care Program (CASCAP) between February 2013 and December 2017. For analysis a multivariate Zero-inflated, Poisson (ZIP) regression model was developed. This model incorporated a conditional autoregressive (CAR) prior structure, with posterior parameters estimated using Bayesian Markov chain Monte Carlo (MCMC) simulation with Gibbs sampling. Covariates included in the models were age, sex, normalized vegetation index (NDVI), and distance to water body. There was a total of 1,299 cases out of 358,981 participants. CCA incidence increased 2.94 fold (95% credible interval [CrI] 2.62–3.31) in patients >60 years as compared to ≤60 years. Males were 2.53 fold (95% CrI: 2.24–2.85) more likely to have CCA when compared to females. CCA decreased with a 1 unit increase of NDVI (Relative Risk =0.06; 95% CrI: 0.01–0.63). When posterior means were mapped spatial clustering was evident after accounting for the model covariates. Age, sex and environmental variables were associated with an increase in the incidence of CCA. When these covariates were included in models the maps of the posterior means of the spatially structured random effects demonstrated evidence of spatial clustering.

Predictors of hookworm and Opisthorchis viverrini infection among adolescents in urban Laos: a cross-sectional study

Purpose: Infection with hookworm and Opisthorchis viverrini are serious health problems among children and adolescents in Laos. In this study, we demonstrated the factors related to hookworm and O. viverrini infection, including primary school health programs, among secondary school students in Vientiane city of Laos.

Material and methods: A cross-sectional survey and stool examination were conducted among secondary school students in Vientiane. One stool sample from each participant was examined using two Kato-Katz smears. Data of 164 participants were analyzed and the associations among parasitic infections, sociodemographic characteristics, and the school health program in primary school were assessed in a univariate logistic regression analysis. Predictors with p<0.25 were retained in a multivariate logistic regression model. Odds ratios (ORs) and 95% confidence intervals (CIs) were reported. The significance level was set at p<0.05.

Results: The infection rates of O. viverrini and hookworm were 39.0% and 36.0%, respectively. Older students (OR=1.55, 95% CI: 1.01–2.37, p=0.046) and those whose father had irregular income (OR=0.47, 95% CI: 0.13–0.93, p=0.036) had a higher risk for hookworm infection. Students whose mother had irregular income (OR=0.30, 95% CI: 0.13–0.69, p=0.005) had a higher risk for O. viverrini infection. Higher primary school health program scores were associated with a lower risk for hookworm infection in the univariate model but not in the multivariate model.

Conclusion: Sociodemographic factors have a strong influence on infections with both hookworm and O. viverrini. Current school health programs in Laos may be insufficient to reduce O. viverrini infections. Other approaches, such as supporting parents in finding employment with regular income, may be needed.

Intestinal helminth infections in HIV-infected patients in Savannakhet after establishment of an HIV registration network in Lao People's Democratic Republic

Background

In Lao People’s Democratic Republic (PDR), which borders China, Vietnam, Cambodia, Thailand, and Myanmar, the number of HIV-infected patients has increased in recent years. HIV-infected patients diagnosed in Lao PDR are enrolled in a registration network and receive antiretroviral therapy (ART) covered by governmental financial support. Based on the registration network, we investigated intestinal helminth infections and coinfection with HTLV-1 in HIV-infected patients treated with an early intervention using ART in Lao PDR.

Methods

This cross-sectional study of all 252 HIV-infected patients at Savannakhet Provincial Hospital, located in the southern part of Lao PDR, was conducted between February and March 2018. Socioepidemiological information and clinical information were collected from a registration network database and by questionnaire administered to participants. Microscopic examination of intestinal helminth infections in stool samples and particle agglutination for anti-HTLV-1 antibody in plasma were performed.

Results

The median age of all 252 participants was 39 years old (range, 18–59). Based on the registration network database, there were 156 (61.9%) HIV-infected patients with a CD4-positive cell count ≥ 200 cells/μL and 146 (57.9%) with an HIV viral load < 250 copies/mL. Among 212 stool samples, 75 (35.4%) were found to contain one or more intestinal helminth species, including Opisthorchis viverrini (16.5%), Strongyloides stercoralis (10.8%), hookworm (10.4%), and Taenia saginata (3.3%). This rate of intestinal helminth infections was lower than that of a previous report conducted before the establishment of the registration network for HIV-infected patients in Lao PDR. There was no significant association between intestinal helminth infections and a lower CD4-positive T cell count or higher HIV viral load. HIV-infected patients with anti-HTLV-1 antibody positivity were not found in this cohort.

Conclusion

The registration network and an early intervention using ART may provide good medical care and improve the clinical course of HIV-infected patients in Lao PDR. However, the incidence of intestinal helminth infections remains high at 35.4%. The development of a specific medical care system for helminth infection for HIV-infected patients is necessary.

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.

Epidemiology of soil transmitted Helminth infections in the middle-belt of Ghana, Africa

BACKGROUND

Helminths are among the most widespread infectious agents prevalent in tropical and sub-tropical regions of the developing world defined by inadequate sanitation, poverty and unsafe water sources. This study was carried out to describe the distribution of helminth and malaria parasite infections in the middle-belt of Ghana in sub-Saharan Africa where disease burden, including anaemia is rife and helminths are perceived to be significant contributors of the burden.

METHODS

A cross-sectional survey involving 1826 residents located in the middle belt of Ghana where no or very little previous community-based helminth work had been carried out. The participants randomly recruited at household level provided biological samples collected over a 12-month period following a rigorous consenting process and these were analysed to describe the different types and seasonal distribution of helminths.

FINDINGS

Overall, 19.3% intestinal helminth infection prevalence was documented. Also based on parasites targeted for elimination, 12.1% Hookworm, 4.0% Hymenolepis nana/Hymenolepis dimunita, 1.5% Ascaris lumbricoides, 1.5% Taenia species, 0.9% Strongyloides stercoralis and 0.8% Trichuris trichiura, with about 1.0% polyphelminthiasis were recorded in the survey. About 55.4% and 44.4% of the participants had heavy hookworm and Trichuris infections respectively. Most of the Ascariasis (83.3%) infections were light in intensity. Hookworm infection was identified with significant odds considering decreasing age (OR = 2.09, p = 0.03), inappropriate footwear use (OR = 1.88, p = 0.021), malaria parasite co-infection (OR = 1.62, p = 0.018), not scrubbing nails during hand washing (OR = 0.68, p = 0.048), source of drinking water (OR = 2.51, p = 0.027) and religion (OR = 4.36, p = 0.002).

CONCLUSIONS

Hookworm infection was significantly higher in younger age groups and among those who did not have safe drinking water. Proper sanitation, protective footwear, religion and good personal hygiene practices were found to influence helminth and hookworm prevalence in the area. Malaria parasite coinfection with helminths, especially hookworm infections increased 2-fold.

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.

Transmission of Opisthorchis viverrini, Schistosoma mekongi and soil-transmitted helminthes on the Mekong Islands, Southern Lao PDR

BACKGROUND

Prevalence of Opisthorchis viverrini, Schistosoma mekongi and soil-transmitted helminths (STH) remains high in Lao People's Democratic Republic (Lao PDR), despite control efforts including mass-drug administration, education and communication campaigns. New approaches are required to advance helminth control.

METHODS

An ecohealth study was conducted on two Mekong islands in Southern Laos. Demographic and behavioural data were collected by questionnaire. Human and animal reservoir stools were examined. Bithynia spp. and Neotricula aperta snails were examined using shedding. Fresh water fish were examined using digestion technique. Multivariate random-effects analysis was used to find risk factors associated with helminth infections.

RESULTS

Human infection rates with O. viverrini, hookworm, S. mekongi, Trichuris trichiura, Ascaris lumbricoides and Taenia spp. were 60.7%, 44.1%, 22.2%, 4.1%, 0.6% and 0.1%, respectively. Heavy intensity infections were 4.2%, 3.6% and 1.8% for O. viverrini, S. mekongi and hookworm, respectively. O. viverrini and S. mekongi infection rates among dogs and cats were 25.0% and 14.7%, respectively. Of the cats tested, 53.1% were infected with O. viverrini. Prevalence of O. viverrini and S. mekongi in snails was 0.3% and 0.01%, respectively. Overall prevalence of O. viverrini infection in fresh water fish was 26.9%, with the highest infection rates occurring in Hampala dispa (87.1%), Cyclocheilichthys apogon (85.7%) and Puntius brevis (40.0%). Illiteracy and lower socioeconomic status increased the risk of O. viverrini infection, while those aged 10-16 years and possessing latrines at home were less likely to be infected. Household dogs and cats that consumed raw fish were significantly and positively associated with O. viverrini infection of the household members. For S. mekongi, children under 9 years old were exposed significantly to this infection, compared to older age groups.

CONCLUSIONS

There is a pressing need to design and implement an integrated helminth control intervention on the Mekong Islands in southern Lao PDR. Given the highly dynamic transmission of O. viverrini, S. mekongi, STH and extended multiparasitism, annual mass-drug administration is warranted along with environmental modifications, health education and improved access to clean water and adequate sanitation to consolidate morbidity control and move towards elimination.

TRAIL REGISTRATION NUMBER

Our findings presented here are from a cross-sectional study, therefore, it has not been registered.

A cross-sectional survey of soil-transmitted helminthiases in two Myanmar villages receiving mass drug administration: epidemiology of infection with a focus on adults

BACKGROUND

Soil-transmitted helminths (STH) are still highly prevalent in southeast Asia. The country of Myanmar has had ongoing mass drug administration (MDA) programmes since 2003 in an attempt to control STH and reduce STH-related morbidities. Whilst the MDA programmes have reported high nationwide coverage, there have been no epidemiological surveys that included measurements from adults. This paper details three cross-sectional surveys that took place over the course of a year in two villages endemic for STH and receiving MDA in lower Myanmar.

RESULTS

At baseline, 27.81% of participants were infected with at least one type of STH. The most prevalent STH was Trichuris trichiura (18.12%) followed by hookworm (8.71%) and Ascaris lumbricoides (5.34%). Most infections were of low intensity, measured by eggs per gram of faeces (EPG). Gender stratification revealed that A. lumbricoides prevalence was significantly higher in females, whereas hookworm prevalence was significantly higher in males. The distribution of EPG in the study sample was highly overdispersed, suggesting that most people release few eggs whereas a few people release many eggs. Adults harbour a major proportion of the overall STH burden; 65.15% of STH infections were harboured by adults.

CONCLUSIONS

STH infection remains at medium prevalence in the study villages despite past and recent MDA. Recorded prevalence of STH in school-aged children has not substantially decreased since the last monitoring and evaluation activities in Myanmar in 2013. Analyses suggest that adults are a major contributor to the total STH prevalence and EPG burden, probably perpetuating transmission.

Prospects and Challenges towards Sustainable Liver Fluke Control

The liver fluke Opisthorchis viverrini (Ov) is endemic in Southeast Asia where more than 10 million people are estimated to be infected. The infection is associated with several hepatobiliary diseases, including cholangiocarcinoma (CCA). Northeast Thailand is a hotspot for Ov transmission, and, despite extensive public health prevention campaigns led by the government, the prevalence of Ov infection is still high. High infection rates result from cultural and ecological complexities where wet-rice agrarian habitats, centuries-old raw-food culture, and the parasite's complex biology combine to create an ideal transmission arena. Here we review the state of our knowledge regarding the social-ecological determinants underlying Ov transmission. We also describe an integrative research rationale for liver fluke control better aligned with sustainable health development.

Role of socio-cultural and economic factors in cyprinid fish distribution networks and consumption in Lawa Lake region, Northeast Thailand: Novel perspectives on Opisthorchis viverrini transmission dynamics

Opisthorchis viverrini (Ov) is a fish-borne parasite endemic in parts of Lao PDR, Cambodia, southern Vietnam and Northeast Thailand (Isaan) where an estimated 10 million people are infected. Human Ov infection, associated with hepatobiliary complications, including cholangiocarcinoma (CCA), occurs when infected fish are consumed raw or undercooked, a longstanding cultural tradition in the region. This mixed- methods descriptive study was carried out in Isaan villages around Lawa Lake, Khon Kaen Province, known for their Ov endemicity. Focus group discussions (FGDs) and in depth interviews (IDIs) were used to explore socio-cultural determinants underlying raw fish consumption practices, and global positioning system (GPS) devices to map local fish distribution networks. Qualitative data affirmed major socio-cultural and dietary lifestyle transitions occurring consequent on recent decades of modernization policies and practices, but also the persistence of Isaan traditional raw-fish eating practices and incorrect beliefs about infection risk avoidance. Fish traders/middlemen purchase most of the catch at the lakeshore and play the dominant role in district market fish distribution networks, at least for the larger and less likely infected, fish species. The lower economic value of the small potentially-infected cyprinid fish means local fishermen typically distribute them free, or sell cheaply, to family and friends, effectively concentrating infection risk in already highly Ov infected villages. Our study confirmed the persistence of traditional Isaan raw-fish meal practices, despite major ongoing socio-cultural lifestyle transitions and decades of Ov infection health education programs. We contend that diffuse socio-cultural drivers underpin this practice, including its role as a valued cultural identity marker. A "fish economics" factor was also evident in the concentration of more likely infected fish back into local villages due to their low economic value at district market level. The complexity of factors supporting "risky" fish-eating traditions in Isaan underscores the importance of integrated liver fluke infection control strategies to draw on transdisciplinary knowledge beyond biomedicine and also embrace participatory protocols for engaging communities in developing, implementing and evaluating interventions.

[Present Situation of Opisthorchiasis in Vientiane Capital, Lao Peoples' Democratic Republic]

Opisthorchiasis is the commonest liver disease caused by Opisthorchis viverrini in Thailand, Lao People's Democratic Republic (PDR) and Cambodia, which will be a major cause of future human cholangiocarcinoma in these regions. In this short review, we describe the epidemic aspects of this parasite infection and the outline of results of our recent surveys of the fluke in humans and its intermediate hosts in Vientiane Capital, where information on the opisthorchiasis epidemic is insufficient. We examined the stool from a total of 296 persons living in the Phailom village (population, 1545, 1999) from 2011 to 2012. As a result, the intestinal parasitism rate was very high from 54 to 59%. Among intestinal infections, O. viverrini infection was observed at highest rates from 51 to 53%. On the other hand, the rate of infection by nematodes was very low. We also conducted intermediate-host investigations in the river and damp areas at 3 villages in the Vientiane capital and 2 villages in Vientiane Province in 2012. As shown by these results, no Opisthorchis species was detected in 147 samples of the host genus Bythinia. However, metacercariae were detected in 3 samples of Cyclocheilichthys sp. and in a Hampala sp. in 303 cyprinid fishes collected from the Haikham village area of Vientiane Capital.

Concomitant helminth infection downmodulates the Vaccinia virus-specific immune response and potentiates virus-associated pathology

The aim of this work was to elucidate the immunopathological mechanisms of how helminths may influence the course of a viral infection, using a murine model. Severe virulence, a relevant increase in the virus titres in the lung and a higher mortality rate were observed in Ascaris and Vaccinia virus (VACV) co-infected mice, compared with VACV mono-infected mice. Immunopathological analysis suggested that the ablation of CD8⁺ T cells, the marked reduction of circulating CD4⁺ T cells producing IFN-γ, and the robust pulmonary inflammation were associated with the increase of morbidity/mortality in co-infection and subsequently with the negative impact of concomitant pulmonary ascariasis and respiratory VACV infection for the host. On the other hand, when evaluating the impact of the co-infection on the parasitic burden, co-infected mice presented a marked decrease in the total number of migrating Ascaris lung-stage larvae in comparison with Ascaris mono-infection. Taken together, our major findings suggest that Ascaris and VACV co-infection may potentiate the virus-associated pathology by the downmodulation of the VACV-specific immune response. Moreover, this study provides new evidence of how helminth parasites may influence the course of a coincident viral infection.

Seasonal and Spatial Environmental Influence on Opisthorchis viverrini Intermediate Hosts, Abundance, and Distribution: Insights on Transmission Dynamics and Sustainable Control

BACKGROUND

Opisthorchis viverrini (Ov) is a complex-life-cycle trematode affecting 10 million people in SEA (Southeast Asia). Human infection occurs when infected cyprinid fish are consumed raw or undercooked. Ov requires three hosts and presents two free-living parasitic stages. As a consequence Ov transmission and infection in intermediate and human hosts are strongly mediated by environmental factors and understanding how environmental variability influences intermediate host abundance is critical. The objectives of this study were 1) to document water parameters, intermediate hosts abundance and infection spatio-temporal variation, 2) to assess their causal relationships and identify windows of transmission risk.

METHODOLOGY/PRINCIPAL FINDINGS

Fish and snails were collected monthly for one year at 12 sites in Lawa Lake, an Ov-endemic region of Khon Kaen Province in Northeast Thailand. Physicochemical water parameters [pH, temperature (Tp), dissolved oxygen (DO), Salinity, electrical conductivity (EC), total dissolved solid (TDS), nitrite nitrogen (NO2-N), lead (Pb), total coliform bacteria (TCB) and fecal coliform bacteria (FCB)] were measured. Multivariate analyses, linear models and kriging were used to characterize water parameter variation and its influence on host abundance and infection prevalence. We found that sampling sites could be grouped in three clusters and discriminated along a nitrogen-salinity gradient where higher levels in the lake's southern region predicted higher Bithynia relative abundance (P<0.05) and lower snail and fish species diversity (P<0.05). Highest Bithynia abundance occurred during rainy season (P<0.001), independently of site influence. Cyprinids were the most abundant fish family and higher cyprinid relative abundance was found in areas with higher Bithynia relative abundance (P<0.05). Ov infection in snails was anecdotal while Ov infection in fish was higher in the southern region (P<0.001) at sites showing high FCB.

CONCLUSIONS/SIGNIFICANCE

Our results indicate that water contamination and waterways configuration can influence freshwater communities' assemblages possibly creating ideal conditions for sustained transmission. Sustainable control may require a better appreciation of the system's ecology with wise governance and development planning particularly in the current context of SEA agricultural intensification and landscape modification.

Seroprevalence of fascioliasis, toxocariasis, strongyloidiasis and cysticercosis in blood samples diagnosed in Medic Medical Center Laboratory, Ho Chi Minh City, Vietnam in 2012

Background

Despite the global effort against neglected tropical diseases (NTDs), developing countries with middle to low income are still burdened by them. Vietnam has been undergoing substantial economic growth and urbanization, but underprivileged people living in rural and suburban areas are still having little access to public health infrastructure and proper sanitation. Hitherto, limited information is available for seroprevalence and risk factors of several parasitic diseases in Vietnam.

Methods

A retrospective study was performed on diagnostic results of Fasciola spp., Toxocara spp., Strongyloides stercoralis and Taenia solium IgG ELISA tests from Medic Medical Center Laboratory, Ho Chi Minh City in 2012. The data were first stratified before statistical analyses were performed. Seroprevalence of fascioliasis, toxocariasis, strongyloidiasis and cysticercosis was determined and the age and gender risk factors were evaluated.

Results

Seroprevalence of fascioliasis, toxocariasis, strongyloidiasis and cysticercosis was 5.9 % (590/10,084; 95 % CI: 5.44–6.36), 45.2 % (34,995/77,356; 95 % CI: 44.85–45.55), 7.4 % (3,174/42,920; 95 % CI: 7.15–7.65) and 4.9 % (713/14,601; 95 % CI: 4.55–5.25), respectively. Co-exposure to multiple parasites was detected in 890 males (45.7 %; 95 % CI: 43.49–47.91) and 1,059 females (54.3 %; 95 % CI: 52.09–56.51). Social structure and differences in behavioural factors caused the gender factor to have a significant effect on the prevalence of all the diseases, while the seropositivity for fascioliasis and strongyloidiasis were age group-related.

Conclusions

The seroprevalence of fascioliasis, toxocariasis, strongyloidiasis and cysticercosis in the blood samples diagnosed in Medic Medical Center Laboratory, Ho Chi Minh City, in year 2012 were comparatively high. The Vietnamese customs and cultures, dietary habits and agricultural practices exposed them to high risk of contracting NTDs. Despite the possibility of false positive results due to antigenic cross-reactions, detection of IgG antibodies remains as a reliable method in sero-epidemiological study as it is non-invasive and demonstrates previous exposure of individuals to the parasites. Besides the implementation of strategies to control these diseases, epidemiological analysis and surveillance of diseases should also be continually strengthened to monitor the effectiveness of regimens and interventions.

Untangling the Complexity of Liver Fluke Infection and Cholangiocarcinoma in NE Thailand Through Transdisciplinary Learning

This study demonstrates how a transdisciplinary learning approach provided new insights for explaining persistent Opisthorchis viverrini infection in northern Thailand, as well as elucidating problems of focusing solely on the parasite as a means of addressing high prevalence of cholangiocarcinoma. Researchers from diverse backgrounds collaborated to design an investigative homestay program for 72 Singaporean and Thai university students in five northeast Thai villages. The students explored how liver fluke infection and potential cholangiocarcinoma development are influenced by local landscape dynamics, aquatic ecology, livelihoods, food culture and health education. Qualitative fieldwork was guided daily by the researchers in a collaborative, co-learning process that led to viewing this health issue as a complex system, influenced by interlinked multidimensional factors. Our transdisciplinary experience has led us to believe that an incomplete understanding of these linkages may reduce the efficacy of interventions. Further, viewing liver fluke infection and cholangiocarcinoma as the same issue is inadvisable. Although O. viverrini infection is an established risk factor for the development of cholangiocarcinoma, multiple factors are known to influence the likelihood of acquiring either. Understanding the importance of the current livelihood transition, landscape modification and the resulting mismatch between local cultures and new socio-ecological settings on cholangiocarcinoma initiation and liver fluke transmission is of critical importance as it may help readjust our view of the respective role of O. viverrini and other socioeconomic risk factors in cholangiocarcinoma etiology and refine intervention strategies. As demonstrated in this study, transdisciplinary approaches have the potential to yield more nuanced perspectives to complex diseases than research that focuses on specific aspects of their epidemiology. They may therefore be valuable when designing effective solutions to context-sensitive diseases such as liver fluke infection and cholangiocarcinoma.

Taenia solium Taeniasis and Cysticercosis in Southeast Asia

Human taeniasis/cysticercosis caused by the pork tapeworm Taenia solium has been identified as a potentially eradicable disease by the International Task Force for Disease Eradication of the World Health Organization. In southeast Asia, T. solium taeniasis/cysticercosis is considered one of the major neglected tropical diseases afflicting the region. In the last few decades, a considerable effort has been invested toward establishing the epidemiology and burden of disease in several southeast Asian countries. Moreover, further evidence is emerging as to understanding the dynamics of disease transmission and cultural, political, and socioeconomic factors influencing the success of control and eradication efforts within the region. However, despite major collaborations by several champion groups, advances have been slow and little remains known about the complete epidemiology of taeniasis/cysticercosis and the barriers to programmatic success. This review article aims to address the above issues with a further focus on the challenges to control and eradicate taeniasis/cysticercosis within the southeast Asia region.

Opisthorchis viverrini infections and associated risk factors in a lowland area of Binh Dinh Province, Central Vietnam

Opisthorchiasis caused by Opisthorchis viverrini is a major public health problem in the Mekong Basin in South East Asia. It is associated with cholangiocarcinoma, a fatal cancer of the bile duct, which is very common in some areas of Thailand and Lao PDR. Although there is evidence of opisthorchiasis in the central and Southern provinces of Vietnam, data are scarce and Vietnam is often not considered an opisthorchiasis endemic area in the international literature. We conducted a cross-sectional survey in June 2015 in a lowland rural area of Binh Dinh Province in Central Vietnam to investigate the apparent prevalence of O. viverrini infection in the population and the associated risk factors. A total of 254 stool samples were collected and examined by the Kato Katz method. Consenting people shedding Opisthorchis-like eggs with their stools were treated with praziquantel and MgSO4 and adult worms were collected from stools for morphological and molecular identifications. Risk factors were studied with a structured questionnaire and the association with infection was evaluated by univariate and multivariate Firth's logistic regression analysis. The apparent prevalence in the investigated population determined by stool examination was 11.4% (CI: 8-16%). Infection with O. viverrini was confirmed in all 11 individuals consenting to receive praziquantel treatment and subsequent worm recovery from stools. The mean number of worms recovered after treatment/purgation was 14.5 (range 2-44). Male gender and the consumption of dishes prepared from raw small wild-caught freshwater fish (Carassius auratus) were found to be significant risk factors associated with opisthorchiasis in the area. These findings confirm the presence of O. viverrini infection in Central Vietnam related to the consumption of raw fish dishes. Awareness campaigns and control programs should be implemented in the region to combat this potentially fatal fluke infection.

Prevalence of Endemic Pig-Associated Zoonoses in Southeast Asia: A Review of Findings from the Lao People's Democratic Republic

The increasing intensification of pork production in southeast Asia necessitates an urgent requirement to better understand the dual impact of pig-associated zoonotic disease on both pig production and human health in the region. Sharing porous borders with five countries and representing many regional ethnicities and agricultural practices, the Lao People's Democratic Republic (Lao PDR) appears well placed to gauge the levels of pig-associated zoonoses circulating in the wider region. Despite this, little is known about the true impact of zoonotic pathogens such as leptospirosis, Trichinella, hepatitis E virus (HEV), Japanese encephalitis (JE), and Taenia solium on human health and livestock production in the country. A comprehensive review of the published prevalences of these five pig-associated zoonoses in Lao PDR has demonstrated that although suspicion remains high of their existence in pig reservoirs across the country, epidemiological data are scarce; only 31 epidemiological studies have been undertaken on these diseases in the past 25 years. A greater understanding of the zoonoses prevalence and subsequent risks associated with pork production in the southeast Asian region could help focus public health and food safety interventions at key points along the value chain, benefiting both livestock producers and the broader animal and human health systems in the region.

Cultural drivers and health-seeking behaviours that impact on the transmission of pig-associated zoonoses in Lao People's Democratic Republic

Pig rearing is an important income source in the Lao People's Democratic Republic (PDR), with many smallholder farmers using traditional free-range pig production systems. Despite the potentially significant health risks posed by pig production regarding pig-associated zoonoses, information on the sociocultural drivers of these zoonoses is significantly lacking. This review summarises the existing sociocultural knowledge on eight pig-associated zoonoses suspected to be endemic in Southeast Asia: brucellosis, Q fever (Coxiella burnetii), trichinellosis, hepatitis E virus, leptospirosis, Japanese encephalitis, Streptococcus suis and Taenia solium taeniasis-cysticercosis. It summarises current knowledge on these diseases grouped according to their clinical manifestations in humans to highlight the propensity for underreporting. A literature search was conducted across multiple databases for publications from 1990 to the present day related to the eight pig-associated zoonoses and the risk and impact connected with them, with Lao PDR as a case study. Many of these pig-associated zoonoses have similar presentations and are often diagnosed as clinical syndromes. Misdiagnosis and underreporting are, therefore, substantial and emphasise the need for more robust diagnostics and appropriate surveillance systems. While some reports exist in other countries in the region, information is significantly lacking in Lao PDR with existing information coming mainly from the capital, Vientiane. The disease burden imposed by these zoonoses is not only characterised by morbidity and mortality, but directly impacts on livelihoods through income reduction and production losses, and indirectly through treatment costs and lost work opportunities. Other factors crucial to understanding and controlling these diseases are the influence of ethnicity and culture on food-consumption practices, pig rearing and slaughter practices, hygiene and sanitation, health-seeking behaviours and, therefore, risk factors for disease transmission. Published information on the knowledge, attitudes and beliefs of people regarding pig zoonoses and their risk factors is also extremely limited in Lao PDR and the broader Southeast Asian region. The need for more transdisciplinary research, using a One Health approach, in order to understand the underlining social determinants of health and their impacts on health-seeking behaviours, disease transmission and, ultimately, disease reporting, cannot be more emphasized.

Subtle to severe hepatobiliary morbidity in Opisthorchis viverrini endemic settings in southern Laos

Evidence of severe hepatobiliary morbidity associated with Opisthorchis viverrini liver fluke infection including cholangiocarcinoma (CCA) is scarce in Laos although O. viverrini infection is highly prevalent. We assessed hepatobiliary morbidity using abdominal ultrasonography (US) in O. viverrini adult patients in Saravan province, Southern Laos. A random sample of 431 O. viverrini patients from 10 villages underwent abdominal US. Mild, moderate and markedly advanced periductal fibrosis was diagnosed in 7.0%, 66.5%, and 17.0% of patients, respectively. Normal liver parenchyma was seen in only 9.5% of patients. Presence of gall stones (13.2%), sludge (1.4%), gall wall thickening (1.2%), bile duct dilatation (1.6%), fatty liver (12.0%), kidney stones (8.6%) and cysts (7.9%) were diagnosed in considerable frequencies. In five patients (1.2%) hepatobiliary lesions suggesting CCA were diagnosed. Tumour markers, i.e. Interleukin-6, plasminogen activator inhibitor and carbohydrate antigen 19-9 were within normal range. The number of CCA suspected liver masses and hepatobiliary morbidity diagnosed among clinically asymptomatic adult patients in O. viverrini endemic area presents a major public health concern in Laos. However, definitive diagnosis of Opisthorchis-related severe sequelae including CCA is urgently needed to gauge the burden of this deadly disease in Laos.

Repeated stool sampling and use of multiple techniques enhance the sensitivity of helminth diagnosis: a cross-sectional survey in southern Lao People's Democratic Republic

Intestinal parasitic infections are common in Lao People's Democratic Republic (Lao PDR). We investigated the accuracy of the Kato-Katz (KK) technique in relation to varying stool sampling efforts, and determined the effect of the concurrent use of a quantitative formalin-ethyl acetate concentration technique (FECT) for helminth diagnosis and appraisal of concomitant infections. The study was carried out between March and May 2006 in Champasack province, southern Lao PDR. Overall, 485 individuals aged ≥6 months who provided three stool samples were included in the final analysis. All stool samples were subjected to the KK technique. Additionally, one stool sample per individual was processed by FECT. Diagnosis was done under a light microscope by experienced laboratory technicians. Analysis of three stool samples with KK plus a single FECT was considered as diagnostic 'gold' standard and resulted in prevalence estimates of hookworm, Opisthorchis viverrini, Ascaris lumbricoides, Trichuris trichiura and Schistosoma mekongi infection of 77.9%, 65.0%, 33.4%, 26.2% and 24.3%, respectively. As expected, a single KK and a single FECT missed a considerable number of infections. While our diagnostic 'gold' standard produced similar results than those obtained by a mathematical model for most helminth infections, the 'true' prevalence predicted by the model for S. mekongi (28.1%) was somewhat higher than after multiple KK plus a single FECT (24.3%). In the current setting, triplicate KK plus a single FECT diagnosed helminth infections with high sensitivity. Hence, such a diagnostic approach might be utilised for generating high-quality baseline data, assessing anthelminthic drug efficacy and rigorous monitoring of community interventions.

An ecological study of Bithynia snails, the first intermediate host of Opisthorchis viverrini in northeast Thailand

Infection with the food-borne trematodiasis, liver fluke Opisthorchis viverrini, is a major public health concern in Southeast Asia. While epidemiology and parasitic incidence in humans are well studied, ecological information on the O. viverrini intermediate hosts remains limited. This study aimed to investigate the factors affecting the distribution and abundance of the first intermediate host, Bithynia siamensis goniomphalos snails. Water quality and snails were sampled in 31 sites in Muang District, Khon Kaen Province, Thailand from June 2012 to January 2013 to characterize the B.s. goniomphalos snail habitats. Species relative abundance and Shannon's diversity and evenness indices were employed to describe snail compositions and diversities across different habitat types. Statistical analyses were conducted to examine the extent to which the water quality variables and species interactions account for the relative abundance of B.s. goniomphalos snails. The results showed that the freshwater habitats of ponds, streams and rice paddies possessed significantly different abiotic water qualities, with water temperature and pH showing distinct statistical differences (P<0.05). Different habitats had different snail diversity and species evenness, with high B.s. goniomphalos snail abundance at rice paddy habitats. The differences in snail abundance might be due to the distinct sets of abiotic water qualities associated with each habitat types. The relative abundance of B.s. goniomphalos snails was found to be negatively correlated with that of Filopaludina martensi martensi snails (r=-0.46, P<0.05), underscoring the possible influence of species interaction on B.s. goniomphalos snail population. Field work observations revealed that rice planting seasons and irrigation could regulate snail population dynamics at rice paddy habitats. This study provides new ecological insights into the factors affecting Bithynia snail distribution and abundance. It bridges the knowledge gap in O. viverrini disease ecology and highlights the potential effect of anthropogenic irrigation practices on B.s. goniomphalos snail ecology.

Multiparasitism and intensity of helminth infections in relation to symptoms and nutritional status among children: a cross-sectional study in southern Lao People's Democratic Republic

The occurrence and spatial distribution of intestinal helminth infection in children is fairly well understood. However, knowledge on how helminth infections govern intestinal morbidity is scarce. We conducted a cross-sectional study to assess and quantify the relationship between single and multiple species helminth infection with clinical and self-reported morbidity indicators and nutritional status in Champasack province, southern Lao People's Democratic Republic (Lao PDR). A random sample of 1313 children, aged 6 months to 12 years, from villages in nine rural districts were enrolled and examined for helminth infection using duplicate Kato-Katz thick smears. Morbidity was assessed by self-reported symptoms, coupled with clinical examination and appraisal of nutritional status and anaemia. Bivariate and multivariate logistic regression was employed to study associations between helminth infection and morbidity indicators and anaemia. We found considerable morbidity among the surveyed children, including hepatomegaly (13.7%), pale conjunctiva (13.2%) and abdominal pain (10.4%). Anaemia was recorded in 60.4% of the children, whilst signs of stunting and low body mass index (BMI) were observed in 49.8% and 33.3% of the surveyed children, respectively. Hookworm and Opisthorchis viverrini were the predominant helminth species with prevalences of 51.0% and 43.3%, respectively. The prevalence of Schistosoma mekongi in the surveyed children was 5.6%. Multiple species helminth infections were recorded in 40.4% of the study cohort. Morbidity was associated with specific helminth species infection (e.g. S. mekongi with hepatomegaly; adjusted odds ratio (aOR): 9.49, 95% confidence interval (CI): 2.07-43.51) and multiparasitism (e.g. two or more helminth species with abdominal pain; aOR: 2.40, 95% CI: 1.46-3.93). Anaemia was associated with hookworm infection (aOR: 1.64, 95% CI: 1.16-2.34) and multiparasitism (aOR: 1.64, 95% CI: 1.18-2.29). Low BMI was associated with O. viverrini infection (aOR: 1.68, 95% CI: 1.14-2.49) and multiparasitism (aOR: 1.42, 95% CI: 1.01-2.00). The multiple strong associations reported here between helminth infections (single or multiple species) and intestinal morbidity among children in rural parts of southern Lao PDR call for concerted efforts to control helminth infections, which in turn might improve children's health and development.

Seasonal cercarial emergence patterns of Opisthorchis viverrini infecting Bithynia siamensis goniomphalos from Vientiane Province, Lao PDR

BACKGROUND

Snail intermediate hosts play a pivotal role in maintaining the life cycles of trematodes, including Opisthorchis viverrini. We investigated the emergence patterns of O. viverrini cercariae infecting Bithynia siamensis goniomphalos at foci in an endemic area in Vientiane Province, Lao PDR.

FINDINGS

Samples of B. s. goniomphalos collected during the hot-dry, rainy and cool-dry seasons were examined for O. viverrini infection by cercarial shedding. Emergence of cercariae from O. viverrini-positive snails was monitored daily from 06:00-18:00 h for seven consecutive days at 2 hourly intervals. Snail infections varied seasonally, being highest in the cool-dry season. Peak cercarial emergence was not consistent in different seasons, occurring between 08.00-10.00 h during the hot-dry season and between 12.00-14.00 h during the rainy and cool-dry seasons. The cercarial output was highest in the hot-dry season. The prevalence of infection and the emergence of cercariae were strongly dependent on snail size.

CONCLUSIONS

This study shows that size of snails and environmental factors (such as season) may affect the emergence patterns of cercariae of O. viverrini in snails. These results have both fundamental and applied implications for opisthorchiasis epidemiology and control.

Prevalence of hookworm infection: a retrospective study in Kumasi

OBJECTIVE

To establish the prevalence of hookworm infection among patients who reported at the parasitology laboratory of the Komfo Anokye Teaching Hospital for intestinal parasitic investigation.

METHOD

This retrospective study covered available data from January 2001 to December 2011. Records of patients referred to the parasitology laboratory of the hospital were manually reviewed for hookworm infection. Data on age, sex and status of hookworm infection (either present or absent) were retrieved and analyzed by using Microsoft Excel 2007 statistical package.

RESULTS

A total of 47 147 patients was reported at the laboratory for intestinal parasitic investigation. Among these patients, 158 patient were positive, representing an overall prevalence of 0.3% (158/47 147). Among the positive cases, the study revealed that the proportion of individuals in age groups <1, 1 to 9, 10 to 19, 20 to 29 and 30 to 39 years were 1.3% (2), 10.8% (17), 16.5% (26), 27.2% (43) and 23.4% (37) respectively. Furthermore, people in age group 40 to 49, 50 to 59 and ≥60 years were infected in the proportion of 8.7% (14), 5.7% (9) and 7.0% (11) respectively. Among the infected patients, the number of females was 62.7% (99) while that of males was 37.3% (59). The yearly prevalence rate dropped consistently from 0.84% in 2001 to 0.11% in 2005. However it increased marginally in 2006 (0.27%) and dropped to 0.00% in 2011.

CONCLUSION

Hookworm infestation was found to be generally high between April and August. However the overall prevalence was relatively low among the study population.