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

Infectious Diseases of Poverty volume 6, Article number: 131 (2017) Cite this article

Abstract

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.

Multilingual abstract

Please see Additional file 1 for translations of the abstract into the five official working languages of the United Nations.

Background

Helminthiases are neglected tropical diseases (NTDs) of major public health concern in many low- and middle-income countries (LMIC) in the tropics and sub-tropics, including in Lao People’s Democratic Republic (Lao PDR) [1,2,3,4]. Liver flukes (Opisthorchis viverrini), blood flukes (Schistosoma mekongi) and soil-transmitted helminths (STH) such as round worm (Ascaris lumbricoides), whipworm (Trichuris trichiura) and two-hookworm species (Ancylostoma duodenale, Necator americanus) are among the most prevalent infections in Lao PDR. O. viverrini is endemic nationwide but is most prevalent in the central and southern parts of the country. It occurs in the lowlands, along the Mekong River, where fish are abundant and local inhabitants prefer to consume traditional dishes prepared with raw fish [1, 4,5,6]. S. mekongi is only endemic in two districts of the most southern province, Champasack, bordering Cambodia [7,8,9,10]. STH are highly prevalent in the northern part of the country and in the mountainous areas along Lao-Vietnamese border [4, 11].

Infections with these helminths negatively affect human health and wellbeing. For example, untreated or chronic infection with O. viverrini may lead to severe hepatobiliary morbidity including cholangiocarcinoma (CCA), a fatal bile duct cancer [12, 13]. Chronic infection with S. mekongi may result in portal hypertension and is associated with peri-portal liver fibrosis [14,15,16,17]. In Champasack Province, O. viverrini and S. mekongi are co-endemic [5, 7, 18], further increasing the risk of hepatobiliary morbidity. Finally, anaemia and undernourishment are associated with long-lasting STH infections [19, 20].

Helminths have complex life cycles; O. viverrini, for example, involves two aquatic intermediate hosts, namely freshwater snails (of the genus Bithynia) and freshwater fish (of the Cyprinidae family). Humans and other mammals are infected by eating raw or undercooked fish [21]. The life cycle of S. mekongi involves humans and other mammals (such as dogs, pigs and possibly rats) [22, 23]. The Neotricula aperta snail, which lives in the crevices of submerged rocks in the Mekong River, serves as intermediate host. The cercariae emerge from the infected snails during the daytime and lie under the water surface [9, 24]. Humans and animals are infected with this parasite via skin penetration when they come into contact with infested waters [8]. Lao PDR adheres to the preventive chemotherapy control strategy promoted by WHO [3, 25, 26]. Over the last decade, considerable efforts were employed to implement this strategy through deworming programmes targeting school-children [27] and through mass-drug administration (MDA) alongside information, education and communication (IEC) campaigns in high risk provinces of the country [28]. Despite these efforts, the prevalence of helminth infections, including multiple infections, remains high in many places [4, 18, 26, 29,30,31]. Given the complexity of the transmission cycle of helminth infections and the risky behaviour of humans in endemic communities, it may be necessary to adapt the control strategy to improve the effectiveness of interventions.

Ecohealth research is an emerging field of research studying human health in close connectivity with the ecosystem [32]. It is increasingly conducted to strengthen the sustainability of infectious disease control programmes [33,34,35] and was widely introduced in Southeast Asia (SEA) by the Canadian International Development Research Centre (IDRC) in the late 2000s [36, 37]. Ecohealth has been defined as follows: i) “EcoHealth involves research and practice to promote sustainability of individuals, animals and biodiversity by linking complex interaction of ecosystem, socio-cultural and economic factors” and ii) “Ecohealth is a comprehensive approach to understanding health at its human, animal and environmental interface in a socio-ecological systems context”. Here, we employ an ecohealth approach to determine the prevalence and risk factors of O. viverrini, S. mekongi and STH infections in humans in the ecological environment of Khong district, where potential animal reservoir and intermediate hosts, like molluscs and fish, live in close connectivity.

Methods

Study area

Khong district is an island district located at the Southern border of Champasack Province, Lao PDR (Fig. 1a). It has an estimated population of 100,000 people and comprises a few dozen islands in the Mekong River (geographical coordinates: 13.57°-14.14°N latitude and 105.44°-106.08°E longitude). The district is a known endemic area for O. viverrini, S. mekongi and STH. Done Khon and Done Som are among the biggest islands and are popular tourist destinations. Done Khon has about 260 households with a total population of 1560 people, while Done Som has some 378 households with a total population of 2344 people.

Fig. 1
figure 1

Study map: a Khong District with main Mekong islands; b Selected western shore of Done Som with human settlements and ecological features. (Source: Google Map)

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Study design and population surveyed

Our cross-sectional study was carried out between October 2011 and August 2012 on Done Khon and Done Som islands. These study sites were selected based on a three-stage random sampling. First, we randomly selected two islands out of 10 known endemic islands for the targeted diseases. For each island, 323 study participants were required based on our sample calculation using a formula of simple random sampling, e.g., Z1- α/2 2 × p(1-p)/d2 with a 30% proportion and 5% precision. Based on previous experiences, about 40% of all study participants (129 persons) failed to submit complete stool samples when they were asked to submit multiple stool samples (i.e., at least two). With this in mind, at least 904 study participants from both islands were required for this study. Second, two villages were selected on each island. Finally, about 30 households in each village were randomly selected to meet the required sample size. All members of the selected households, aged 2 years and older and available on the survey day, were invited to participate in the study.

Potential animal reservoir hosts, i.e., dogs, cats, pigs and buffaloes, from selected households were also enrolled and examined for helminth infections. Due to the small numbers of these animals in the study villages (0.4 animals per household; from village record), we examined all of those present during the survey. Village health volunteers helped to identify the domestic animals and conduct follow-up examinations.

We collected intermediate hosts for O. viverrini (Bithynia spp. snails and Cyprinoid fish) and for S. mekongi (Neotricula aperta snails) from selected sites in the study villages and examined them for infection (Fig. 1b).

Snails of the genus Bithynia spp. were collected with a scoop [38] from water bodies near the study villages (e.g., ponds, canals, and rice fields). From each water body, 5–10 sites with an area of 1 × 1 m were identified as collecting points. All Bithynia snails collected from each site were counted, recorded and examined separately. Cyprinoid freshwater fish were captured from the same selected water bodies as well as from the Mekong using a fishing net. Each captured fish was measured for length and weight and were examined at the field station for the presence of O. viverrini metacercariae.

N. aperta snails [39] live in the rocky area of the Mekong River. We identified 10 sites along the Mekong River, where water was frequently used by study villagers for their daily needs. Submerged stones were dredged and snails were hand-picked from them [38]. At each site, N. aperta snails were collected for 20 min by five malacologists. All collected snails were counted, placed in a plastic bag and carried to the field station for examination.

Field procedures and laboratory examinations

In each village, a house, school or temple was identified as a field study station. Two questionnaires were administered to all participating households. A household questionnaire was administered to the heads of households for collecting data on household characteristics (e.g., building type, toilette and water supply), asset ownership (e.g., farm engine, boat, car, motorbike, electricity, television, bicycle, telephone and agriculture land) and animal ownership (e.g., buffalo, cow, goat and pig). An individual questionnaire was used to interview all household members to collect demographic data (e.g., age, sex, educational attainment and professional activities and behavioural risks (e.g., food consumption habits, water contact, animal raising and personal hygiene). Parents or legal guardians answered for children under 10 years of age.

Eligible study participants were invited to submit two stool samples over consecutive days for parasitological analysis. The first stool container (pre-labelled with participant’s name, unique identity number, age and date of collection) was handed to the study participants on the registration day, along with a detailed explanation of stool collection. The second empty container was handed out after study participants returned the first filled container.

Two Kato-Katz (KK) thick smears [40] were prepared from each stool sample (i.e. four smears per person) and examined under light microscopes by an experienced technician within 1 h of sample preparation. Eggs were counted and recorded for each helminth species separately.

We collected faecal samples from potential domestic reservoir animals owed by study households, namely cats, dogs, pigs and water buffaloes. To collect fresh faecal samples [41] from small animals (cats, dogs and pigs), rectal enemas were performed using Sodium Chloride (NaCl) solution and petroleum jelly lubricant. Faecal samples from water buffaloes were collected by rectal swab. All faecal samples were immediately preserved in a 10% formalin solution and transported to the National Institute of Public Health (NIOPH), Vientiane, for processing using the formalin ether concentration technique (FECT) [42].

Bithynia spp. and N. aperta snails were examined for the presence of cercariae infection using the shedding test, previously described by Sri-Aroon and colleagues [43]. In summary, the fresh water snails were put into a transparent plastic container filled with Mekong water and exposed to artificial light. After 2 h, the container was examined under a stereoscope for the presence of cercariae. The infected snails were identified, counted and recorded separately.

The species identification of captured Cyprinoid fish was performed based on guidelines available at FishBase website [44, 45]. Fish digestion was performed using the pepsin enzyme digestion technique [25]. The residue was examined for the presence of O. viverrini metacercariae. The metacercariae were counted and recorded for each infected fish.

Data management and analysis

Information from questionnaires and data forms were double entered into EpiData, version 3.1 (EpiData Association; Odense, Denmark) and validated for their correctness and completeness. Statistical analyses were performed with STATA, version 13.1 (StataCorp., College Station, USA). Only study participants with at least two KK thick smear examinations and with complete questionnaires were retained in the final analysis. Participants were stratified into five age groups: (i) ≤ 9 years, (ii) 10–16 years, (iii) 17–36 years, (iv) 37–50 years, and (v) ≥ 51 years. Socioeconomic status (SES) of the household was calculated using an asset-based method. Indicator data were defined by principal component analysis (PCA). The procedure is widely used and details can be found elsewhere [5, 46, 47]. SES conditions in the household were categorized into one of five wealth quintiles, namely (i) most poor, (ii) very poor, (iii) poor, (iv) less poor, and (v) least poor according to their cumulative standardized asset scores. Details of this widely used approach have been presented elsewhere [5].

The intensity of helminth egg counts was expressed as eggs per gram of stool (EPG) obtained from Kato-Katz examination. Based on WHO recommendations, infection intensity was classified as light (O. viverrini: 1-999 EPG; S. mekongi: 1-100 EPG; hookworm: 1-1999 EPG; T. trichiura: 1-999 EPG; A. lumbricoides: 1-4999 EPG), moderate (O. viverrini: 1000-9999 EPG; S. mekongi: 101-400 EPG; hookworm: 2000-3999 EPG; T. trichiura: 1000-9999 EPG; A. lumbricoides: 5000-49,999 EPG), and heavy (O. viverrini: 1-999 EPG; S. mekongi: 1-100 EPG; hookworm: 1-1999 EPG; T. trichiura: 1-999 EPG; A. lumbricoides: 1-4999 EPG), respectively [25, 31, 48].

Prevalence of parasitic infections was determined and stratified by age, sex and study area (Done Khon versus Done Som). Chi-square test was used to examine the association among categorical variables. The geometric mean for helminth egg counts was calculated for infected individuals. Univariate random-effects logistic regression analysis was used to associate O. viverrini and S. mekongi infections (outcome) with potential risk factors (predictors). The crude odds ratio (cOR), 95% confidence interval (95% CI) and P-value were calculated. Explanatory variables with a P-value of <15% were included in the stepwise multivariate random-effects logistic regression model. Adjusted odds ratio (aOR) was calculated. Smoothed age distribution of O. viverrini, S. mekongi, hookworm and T. trichiura infections by gender was established. Statistical significance was defined as yielding a P-value smaller than 0.05.

Results

Characteristics of the study participants

A total of 994 study participants were included in this final analysis (Fig. 2). Of these, 475 (47.8%) were from Done Khon and 519 (52.2%) from Done Som. There were slightly more female than male participants (51.8% vs 48.2%). Age ranged from 2 to 88 years (median age 29.8 years). The schooling rates did not differ between the two study islands. Subsistent rice farming and fishing were the main professional activities (60.0%). Less than half of the study participants reported having access to a latrine at home (Done Khon 49.7%, Done Som 38.9%). People living in Done Som had a lower socioeconomic status than in Done Khon (Most poor, 25.8% vs 16.4%, respectively). The sociodemographic characteristics of study participants are summarized in Table 1.

Fig. 2
figure 2

Study diagram

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Table 1 Socio-demographic characteristics of study participants from two study islands (Done Khon and Done Som, Khong District (n = 994)
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Helminth infections in humans

Helminth infections were very frequent on the two islands. O. viverrini, hookworm, S. mekongi, and T. trichiura were found in 60.7%, 44.1%, 22.2% and 4.1% of the participants, respectively. Very few participants were infected with A. lumbricoides (0.6%) and Taenia spp. (0.1%). The prevalence of O. viverrini was almost two-times higher in Done Som compared to Done Khon (77.3% vs. 42.5%, P < 0.001). S. mekongi prevalence was similar on both islands (P = 0.329). Multi-parasitism was diagnosed in 40.5% of the study participants. Details of the helminth infections are given in Table 2.

Table 2 Prevalence of Opisthorchis viverrini, Schistosoma mekongi, soil-transmitted helminth and other intestinal helminth infections among study participants from two islands (Done Khon and Done Som) of Khong District (n = 994)
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Figure 3 displays the smoothed age prevalence of helminth infections by gender. O. viverrini infection appears to be acquired at a young age, with prevalence increasing gradually (Fig. 3a). Hookworm infection is acquired at a very young age. For males, the prevalence peaked among adolescents aged 10–20 years and plateaued among older age groups. For females, prevalence peaked between 10 and 20 years old and again after 50 years old (Fig. 3b). For males, two prevalence peaks were observed; the first among children under 10 years old and the second among adults between 40 and 50 years old. For females, only one peak was seen among children under 10 years old. T. trichiura prevalence was distributed similarly among males and females independent of age (Fig. 3c). S. mekongi prevalence was differently distributed among males and females (Fig. 3d).

Fig. 3
figure 3

Age distribution of major helminth infections by gender on Done Khon and Done Som islands. The figures represent the smoothed age distribution of male (solid line) and female (dotted line) study participants for an infection with (a): Opisthorchis viverrini, (b): hookworm, (c): Trichuris trichiura and (d): Schistosoma mekongi

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Human helminth infection intensities are summarized in Table 3. Most helminth infections were categorized as light infections. Nevertheless, O. viverrini, S. mekongi and hookworm accounted for infections of heavy intensity in some cases (4.2%, 3.6% and 1.8%, respectively).

Table 3 Infection intensity of Opisthorchis viverrini, Schistosoma mekongi and soil-transmitted helminths among study participants from two islands (Done Khon and Done Som) of Khong District (n = 994)
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Prevalence of helminth infections in animal reservoirs and intermediate hosts

Table 4 summarizes the results of infections in animals, snails and Cyprinoid fish. Analysis of animal faeces showed that overall prevalence of O. viverrini infection in cats, dogs and pigs was 53.1%, 25.0% and 0.9%, respectively, while only dogs (14.7%) were found to be infected with S. mekongi. Examination of intermediate host snails for O. viverrini (Bithynia spp.,) and for S. mekongi (N. aperta) detected infection rates of 0.3% and 0.01%, respectively (Table 4). A similar rate of O. viverrini infection was found in Bithynia spp. from Done Khon and Done Som (0.1% vs. 0.5%, P = 0.045), while only the N. aperta snails from Done Khon (0.02%) were found to be infected with S. mekongi.

Table 4 Prevalence of Opisthorchis viverrini and Schistosoma mekongi infections in animals on Done Khon and Done Som islands
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Table 5 displays the prevalence of O. viverrini infection in the Cyprinoid fish collected from habitats in Done Khon and Done Som islands. In total, 628 fish representing 21 species were digested and examined. Of these, 622 represented 19 species of Cyprinoid fish, five fish were from the Osphronemidiae family and one fish from the Anabantidae family. Only Cyprinoidae fish species were infected with O. viverrini, with an overall prevalence of 26.9% and an average of 228.7 metacercariae per fish. The highest infection intensity was seen in Cyclocheilichthys apogon, with an average of 168.7 metacercariae per infected fish. Only one fish of the Anabas testudineus from Anabantidae family was examined. It was found positive for minute intestinal fluke metacercariae.

Table 5 Prevalence of Opisthorchis viverrini and minute intestinal flukes (MIF) metacercariae in cyprinoid fish from Done Khon and Done Som islands
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Risk factor analysis for O. viverrini and S. mekongi infections in human

Table 6 shows the association between risk factors of O. viverrini  and S. mekongi  infections. The stepwise multivariate analysis showed that illiteracy (illiteracy vs. preschool children: aOR = 6.0, 95% CI: 3.3–11.0), P = 0.028) and lower socioeconomic status were associated with an increased risk of being infected with O. viverrini (less poor vs least poor: aOR = 3.1, 95% CI: 1.7–7.5, P = 0.013), while school children in the age group 10–16 years (aOR = 0.1, 95% CI: < 0.1–0.4, P = 0.003) and those with a latrine at home (aOR = 0.2, 95% CI: 0.1–0.4), P = 0.001) were more likely to be protected against the infection. Furthermore, having household dogs and cats that eat raw fish was significantly and positively associated with O. viverrini infection of the household members (aOR = 1.9, 95% CI: 1.2–3.1, P = 0.007). The age group was the only factor significantly associated with S. mekongi infection. Children in the age group ≤9 years old were significantly exposed to this infection compared to older age groups (age group 10–16: aOR = 0.5, 95% CI: 0.2–0.9, P = 0.047, age group 17–36: aOR = 0.2, 95% CI: < 0.1–0.8, P = 0.022; age group 37–50: aOR = 0.2, 95% CI: < 0.1–0.8, P = 0.021 and age group ≥51: aOR = 0.2, 95% CI: < 0.1–0.8, P = 0.024). The model revealed that age group (10–16 year: aOR = 1.7, 95% CI: 1.1–2.7, P = 0.015), educational level (illiteracy: aOR = 7.4, 95% CI: 3.2–17.3, P < 0.001, and primary school: aOR = 4.8, 95% CI: 2.0–11.3, P < 0.001) and raising pigs at home (aOR = 1.3, 95% CI: 1.1–1.7, P = 0.047) were significant risk factors for STH infection, while being a women (aOR = 0.4, 95% CI: 0.3–0.6, P < 0.001) or having a latrine at home (aOR = 0.6, 95% CI: 0.4–0.8, P < 0.001) were protective factors.

Table 6 Stepwise multivariate logistic regression (backward elimination) analyses the association between underlying risk factors and O. viverrini, S. mekongi and STH infections among study participants on both islands (Done Khon and Done Som islands (n = 994)
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Discussion

The Khong District, with its dozens of islands in the Mekong, has a distinct ecological setting (Fig. 1). Human settlements line the island shores, while the rest of the island is used for agricultural activities, particularly rice farming. The Mekong River as well as the diverse water bodies on the islands represent a rich ecosystem for fish and mollusc populations. On two Mekong islands, highly endemic for multiple species of helminth infections, we studied the transmission of O. viverrini, S. mekongi and STH using an ecohealth approach [32, 37] to better assess the relation of human infection status to environmentally present reservoir and intermediate hosts. Heavy infections and multi-parasitism were prevalent among the human population and age-gender distributions revealed parasite-specific patterns. Examination of potential animal reservoir hosts from the study participants’ households (cats, dogs, pigs and buffaloes) yielded ten different helminth species, with many of them having zoonotic capacity. Infection rates of intermediate snail hosts Bithynia sp. and N. aperta were low but reflect on-going transmission. In addition, infection rates of locally caught cyprinoid fish with O. viverrini and minute intestinal fluke (MIF) metacercariae were very high, pointing to a high risk of infection when they are consumed raw or undercooked.

In this study, we document high infection rates of O. viverrini, S. mekongi and selected species of STH, namely hookworm infections. The high infection rates are a surprise given that MDA campaigns were conducted annually between 2008 and 2013 [26], in which praziquantel (40 mg/kg BW single dose) and albendazole (400 mg single dose) were provided to the entire population (older than 4 years). In addition, biannual deworming (with mebendazole) takes place in all Lao primary schools [27]. Local health authorities confirmed that all Mekong islands were targeted, but we could not find coherent information on the number of treatment rounds conducted on our study islands. Nevertheless, our results indicate that the impact of the intervention is insufficient.

The Ministry of Health’s objective is to eliminate S. mekongi as a public health problem in Lao PDR by 2016. On our study islands, S. mekongi cannot be considered eliminated given the high infection rates. Our data indicate that S. mekongi infection in dogs may fuel the transmission by constantly infecting Neotricula populations in the Mekong. Of similar importance are cats and dogs for the transmission of O. viverrini. Hence, animal reservoirs in households should also be a target of integrated parasite control on the Mekong islands, and throughout Lao PDR.

Several factors might account for the persisting high O. viverrini infection rates among humans on the Mekong islands. One such factor is the high infection prevalence among cyprinoid fish. More than 80 species of the Cyprinidae family and at least 13 species of other families can serve as a secondary intermediate host [25]. In our study, O. viverrini metacercariae were identified in 11 cyprinoid fish species, while some had particularly high O. viverrini metacercariae infection rates, e.g. in 87.1% of Hampala dispa. All the cyprinoid species in which we detected an infection are known to be good O. viverrini transmitting species [49,50,51,52]. They were identified in all water bodies examined in this study. Fish are mostly likely infected while small and living in rice fields, canals and ponds. The metacercariae remain alive as the fish grow and move into the Mekong.

Cyprinoid fish accumulate the metacercariae over a long time. Low infection rates in Bithynia snails may be sufficient for transmission [53]. We found a low infection rate of 0.3% in Bithynia sp. snails. Other studies have detected infection rates between 0.3–8.3% [54]. But infection rates may vary considerably, depending on sampling locality and season [54, 55]. It is important to note that even low infection prevalence rates are sufficient for maintaining transmission.

We observed low S. mekongi infection rates in N. aperta (0.02%) compared to other reports. The presence of infected molluscs gives evidence that S. mekongi transmission is currently on-going. Therefore, abandoning control activities would inevitably lead to an increase in infection rates among humans. There are many more S. mekongi endemic Mekong islands, which might display a different N. aperta population distribution and infection pattern [9, 10].

A major finding from our study is the dramatically high helminth infection rates among domestic cats, dogs, pigs and buffaloes. Ten different parasite species were detected in these animal hosts residing in the households of our study participants. By using FECT, we could distinguish O. viverrini eggs in dogs and cats from other small trematode eggs. Our results showed higher rates than Aunpromma et al. (2012) found in neighbouring Thailand, where 0.37% and 35.5% of the dogs and cats were infected, respectively [56]. The infection rate among dogs, in particular, was 20 times higher than that found in the study of Aunpromma et al. (2012). Through observation and from interviewing animal owners in both communities, it appears that most of the dogs and cats were free-roaming and usually accompanied their owners to the rice field where they caught and ate fish directly from the canals or rice fields. Moreover, raw and undercooked fish were often fed to these animals. These phenomena, in combination with the high infection rates of dogs and cats, likely maintain the transmission of O. viverrini and other fish-borne trematode infections in the communities.

Only dogs were diagnosed with S. mekongi in this study, which is consistent with other study findings [9, 22]. We did not find any S. mekongi eggs in pigs or water buffaloes, though both animals were found to be infected in earlier investigations [57]. However, they are not of importance for transmission on our study islands. On other Mekong islands where these animals are more free-roaming, their infection status could be higher and, thus, their contribution to transmission of greater importance.

The results of our risk factor analysis for O. viverrini infection differed from many previous studies [5, 30, 49]. More than half of our risk factors dropped out after multivariate analysis, whereas the initial univariate analysis showed significant associations between infection and age group, occupation, socioeconomic status, latrine availability, history of open defecation this year, and eating raw and/or undercooked fish (Table 6). The association between O. viverrini and socioeconomic status was not clear for our study population. The study area was geographically very small. Therefore, the variation in socioeconomic status and living conditions might not have varied enough to results in risk differentiation. Furthermore, control activities such as the annual treatments between 2008 and 2013, have had an impact on infection status, which in turn might have blurred important associations. For example, eating raw/undercooked fish was not significantly associated with O. viverrini infection, although deeply rooted habits of eating raw or improperly cooked fish is a well-known factor in sustaining helminth infections in humans and difficult to control [30, 53, 58].

In our multivariable analysis, we did not find any association between S. mekongi infection and risk factors, except for age. Children under 9 years old had a higher risk of infection than older study participants. This result is likely due to MDA over the years having reduced infection rates among older villagers. Therefore, controls targeting lower age groups could further contribute to eliminating S. mekongi on the Mekong islands.

Our study suffers from some limitations. Our diagnostic procedure most likely underestimated the true infection burden. Although examining a duplicate Kato-Katz thick smear per faecal sample has a considerably higher sensitivity than a single smear, the egg detection rate remains far below that of a multiple stool sample diagnostic procedure [5, 18]. Furthermore, the Kato-Katz technique cannot differentiate small trematode eggs [59]. It is therefore possible that some of the infections in humans were counted as O. viverrini infections instead of MIF.

Conclusions

We conclude that human intestinal helminth infections, namely O. viverrini, S. mekongi and hookworms are still highly endemic on the Mekong islands in Khong District. The low prevalence of O. viverrini and S. mekongi infection in intermediate snail hosts point at on-going transmission. Animal reservoir hosts, particularly cats and dogs, have high O. viverrini infection rates, while only dogs are infected with S. mekongi. An appropriate integrated control approach involving interventions targeting human behaviour, animal reservoirs, and environmental modification might improve the effectiveness of interventions and lead to the elimination of infections.

Abbreviations

95% CI :

95% confidence interval

A. duodenale :

Ancylostoma duodenale

A. lumbricoides :

Ascaris lumbricoides

aOR :

Adjusted odds ratio

BW:

Body weight

CCA:

Cholangiocarcinoma

cOR:

Crude odds ratio

EPG:

Eggs per gram of stool

FECT:

Formalin ether concentration technique

IEC:

Information, education and communication

KAPP:

Knowledge, attitude, practice and perception

Lao PDR:

Lao People’s Democratic Republic

LMIC:

Low and middle income countries

MDA:

Mass drug administration

MIF:

Minute intestinal flukes

N. americanus :

Necator americanus

N. aperta :

Neotricula aperta

NaCl:

Sodium chloride

NIOPH:

National Institute of Public Health

NTDs:

Neglected tropical diseases

O. viverrini :

Opisthorchis viverrini

PCA:

Principle Component Analysis

S. mekongi :

Schistosoma mekongi

S. stercoralis :

Strongyloides stercoralis

STH:

Soil transmitted helminth

T. trichiura :

Trichuris trichiura

WHO:

World Health Organization

References

  1. Sripa B, Kaewkes S, Intapan PM, Maleewong W, Brindley PJ. Food-borne trematodiases in Southeast Asia epidemiology, pathology, clinical manifestation and control. Adv Parasitol 2010;72:305-50.

  2. Utzinger J, Bergquist R, Olveda R, Zhou XN. Important helminth infections in Southeast Asia diversity, potential for control and prospects for elimination. Adv Parasitol. 2010;72:1–30.

    Article  PubMed  Google Scholar 

  3. WHO. Prevention and control of schistosomiasis and soil-transmitted helminthiasis: first report of the joint WHO expert committees. Geneva: World Health Organization Technical Report Series No 912; 2002. p. 912.

    Google Scholar 

  4. Rim HJ, Chai JY, Min DY, Cho SY, Eom KS, Hong SJ, Sohn WM, Yong TS, Deodato G, Standgaard H, et al. Prevalence of intestinal parasite infections on a national scale among primary schoolchildren in Laos. Parasitol Res. 2003;91(4):267–72.

    Article  PubMed  Google Scholar 

  5. Sayasone S, Mak TK, Vanmany M, Rasphone O, Vounatsou P, Utzinger J, Akkhavong K, Odermatt P. Helminth and intestinal protozoa infections, multiparasitism and risk factors in Champasack province, Lao People's Democratic Republic. PLoS Negl Trop Dis. 2011;5(4):e1037.

    Article  PubMed  PubMed Central  Google Scholar 

  6. Xayaseng V, Phongluxa K, van Eeuwijk P, Akkhavong K, Odermatt P. Raw fish consumption in liver fluke endemic areas in rural southern Laos. Acta Trop. 2013;127(2):105–11. doi: 110.1016/j.actatropica.2013.1003.1016. Epub 2013 Apr 1016

    Article  PubMed  Google Scholar 

  7. Sayasone S, Rasphone O, Vanmany M, Vounatsou P, Utzinger J, Tanner M, Akkhavong K, Hatz C, Odermatt P. Severe morbidity due to Opisthorchis Viverrini and Schistosoma Mekongi infection in Lao People's Democratic Republic. Clin Infect Dis. 2012;55(6):e54–7.

    Article  PubMed  Google Scholar 

  8. WHO. The control of schistosomiasis. Second report of the WHO expert committee. World Health Organ Tech Rep Ser. 1993;830:1–86.

    Google Scholar 

  9. Urbani C, Sinoun M, Socheat D, Pholsena K, Strandgaard H, Odermatt P, Hatz C. Epidemiology and control of mekongi schistosomiasis. Acta Trop. 2002;82(2):157–68.

    Article  CAS  PubMed  Google Scholar 

  10. Muth S, Sayasone S, Odermatt-Biays S, Phompida S, Duong S, Odermatt P. Schistosoma Mekongi in Cambodia and Lao People's Democratic Republic. Adv Parasitol. 2010;72:179–203.

    Article  PubMed  Google Scholar 

  11. Laymanivong S, Hangvanthong B, Keokhamphavanh B, Phommasansak M, Phinmaland B, Sanpool O, Maleewong W, Intapan PM. Current status of human hookworm infections, ascariasis, trichuriasis, schistosomiasis mekongi and other trematodiases in Lao People's Democratic Republic. Am J Trop Med Hyg. 2014;90(4):667–9.

    Article  PubMed  PubMed Central  Google Scholar 

  12. Sripa B, Bethony JM, Sithithaworn P, Kaewkes S, Mairiang E, Loukas A, Mulvenna J, Laha T, Hotez PJ, Brindley PJ. Opisthorchiasis and Opisthorchis-associated cholangiocarcinoma in Thailand and Laos. Acta Trop. 2011;120(Suppl 1):S158–68.

    Article  PubMed  Google Scholar 

  13. Sripa B. Pathobiology of opisthorchiasis: an update. Acta Trop. 2003;88(3):209–20.

    Article  CAS  PubMed  Google Scholar 

  14. Richter J, Azoulay D, Dong Y, Holtfreter MC, Akpata R, Calderaro J, El-Scheich T, Breuer M, Neumayr A, Hatz C, et al. Ultrasonography of gallbladder abnormalities due to schistosomiasis. Parasitol Res. 2016;115(8):2917–24.

    Article  PubMed  Google Scholar 

  15. Keang H, Odermatt P, Odermatt-Biays S, Cheam S, Degremont A, Hatz C. Liver morbidity due to Schistosoma Mekongi in Cambodia after seven rounds of mass drug administration. Trans R Soc Trop Med Hyg. 2007;101(8):759–65.

    Article  CAS  PubMed  Google Scholar 

  16. Dumurgier C, Tay KH, Surith TN, Rathat C, Buisson Y, Monchy D, Sinuon M, Socheat D, Urbani C, Chaem S, et al. Place of surgery in the prevention of recurrences of digestive haemorrhages at the patients presenting a portal hypertension due to Schistosoma Mekongi. Bulletin de la Societe de pathologie exotique (1990). 2006;99(5):365–71.

    CAS  Google Scholar 

  17. Monchy D, Dumurgier C, Heng TK, Hong K, Khun H, Hou SV, Sok KE, Huerre MR. Histology of liver lesions due to Schistosoma Mekongi. About six cases with severe portal hypertension operated in Cambodia. Bulletin de la Societe de pathologie exotique (1990). 2006;99(5):359–64.

    CAS  Google Scholar 

  18. Vonghachack Y, Sayasone S, Bouakhasith D, Taisayavong K, Akkavong K, Odermatt P. Epidemiology of Strongyloides stercoralis on Mekong islands in southern Laos. Acta Trop. 2015;141PB:289–94. doi:10.1016/j.actatropica.2014.1009.1016. Epub 2014 Oct 1015

    Article  Google Scholar 

  19. Matangila JR, Doua JY, Linsuke S, Madinga J. Inocencio da Luz R, van Geertruyden JP, Lutumba P: malaria, schistosomiasis and soil transmitted helminth burden and their correlation with anemia in children attending primary schools in Kinshasa. Democratic Republic of Congo PLoS One. 2014;9(11):e110789.

    PubMed  Google Scholar 

  20. Soares Magalhaes RJ, Langa A, Pedro JM, Sousa-Figueiredo JC, Clements AC, Vaz Nery S. Role of malnutrition and parasite infections in the spatial variation in children's anaemia risk in northern Angola. Geospat Health. 2013;7(2):341–54.

    Article  PubMed  Google Scholar 

  21. Kaewkes S. Taxonomy and biology of liver flukes. Acta Trop. 2003;88(3):177–86.

    Article  PubMed  Google Scholar 

  22. Strandgaard H, Johansen MV, Pholsena K, Teixayavong K, Christensen NO. The pig as a host for Schistosoma mekongi in Laos. J Parasitol. 2001;87(3):708–9.

    Article  CAS  PubMed  Google Scholar 

  23. Kitikoon V, Schneider CR, Sornmani S, Harinasuta C, Lanza GR. Mekong schistosomiasis. 2. Evidence of the natural transmission of Schistosoma japonicum, Mekong strain, at Khong Island, Laos. Southeast Asian J Trop Med Public Health. 1973;4(3):350–8.

    CAS  PubMed  Google Scholar 

  24. Shimada M, Kato-Hayashi N, Chigusa Y, Nakamura S, Ohmae H, Sinuon M, Socheat D, Kitikoon V, Matsuda H. High susceptibility of Neotricula aperta gamma-strain from Krakor and Sdau in Cambodia to Schistosoma Mekongi from Khong Island in Laos. Parasitol Int. 2007;56(2):157–60.

    Article  PubMed  Google Scholar 

  25. WHO. Control of foodborne trematode infections. Report of a WHO study group. World Health Organ Tech Rep Ser. 1995;849:1–157.

    Google Scholar 

  26. WHO: Report of the WHO expert consultation on Foodborne Trematode infections and Taeniasis/Cysticercosis. World health organ tech rep ser 2011, WHO/HTM/NTD/PCT/20113 2011.

    Google Scholar 

  27. Phommasack B, Saklokham K, Chanthavisouk C, Nakhonesid-Fish V, Strandgaard H, Montresor A, Shuey DA, Ehrenberg J. Coverage and costs of a school deworming programme in 2007 targeting all primary schools in Lao PDR. Trans R Soc Trop Med Hyg. 2008;102(12):1201–6.

    Article  PubMed  Google Scholar 

  28. Phongluxa K, van Eeuwijk P, Soukhathammavong PA, Akkhavong K, Odermatt P. Perceived illness drives participation in mass deworming campaigns in Laos. Acta Trop. 2015;141(Pt B):281–8. doi: 210.1016/j.actatropica.2014.1003.1022. Epub 2014 Apr 1015

    Article  PubMed  Google Scholar 

  29. Aye Soukhathammavong P, Rajpho V, Phongluxa K, Vonghachack Y, Hattendorf J, Hongvanthong B, Rasaphon O, Sripa B, Akkhavong K, Hatz C, et al. Subtle to severe hepatobiliary morbidity in Opisthorchis Viverrini endemic settings in southern Laos. Acta Trop. 2015;141(Pt B):303–9. doi: 310.1016/j.actatropica.2014.1009.1014. Epub 2014 Sep 1029

    Article  PubMed  Google Scholar 

  30. Forrer A, Sayasone S, Vounatsou P, Vonghachack Y, Bouakhasith D, Vogt S, Glaser R, Utzinger J, Akkhavong K, Odermatt P. Spatial distribution of, and risk factors for, Opisthorchis Viverrini infection in southern Lao PDR. PLoS Negl Trop Dis. 2012;6(2):e1481.

    Article  PubMed  PubMed Central  Google Scholar 

  31. Sayasone S, Vonghajack Y, Vanmany M, Rasphone O, Tesana S, Utzinger J, Akkhavong K, Odermatt P. Diversity of human intestinal helminthiasis in Lao PDR. Trans R Soc Trop Med Hyg. 2009;103(3):247–54.

    Article  PubMed  Google Scholar 

  32. Leung Z, Middleton D, Morrison K. One health and EcoHealth in Ontario: a qualitative study exploring how holistic and integrative approaches are shaping public health practice in Ontario. BMC Public Health. 2012;12:358.

    Article  PubMed  PubMed Central  Google Scholar 

  33. Asakura T, Mallee H, Tomokawa S, Moji K, Kobayashi J. The ecosystem approach to health is a promising strategy in international development: lessons from Japan and Laos. Glob Health. 2015;11:3.

    Article  Google Scholar 

  34. Furie GL, Balbus J. Global environmental health and sustainable development: the role at Rio+20. Cien Saude Colet. 2012;17(6):1427–32.

    Article  PubMed  Google Scholar 

  35. Nguyen V, Nguyen-Viet H, Pham-Duc P, Stephen C, McEwen SA. Identifying the impediments and enablers of ecohealth for a case study on health and environmental sanitation in Ha Nam. Vietnam Infect Dis Poverty. 2014;3(1):36. doi:10.1186/2049-9957-1183-1136. eCollection 2014

    Article  PubMed  Google Scholar 

  36. Nguyen-Viet H, Doria S, Tung DX, Mallee H, Wilcox BA, Grace D. Ecohealth research in Southeast Asia: past, present and the way forward. Infect Dis Poverty. 2015;4:5. doi:10.1186/2049-9957-1184-1185. eCollection 2015

    Article  PubMed  PubMed Central  Google Scholar 

  37. Kingsley J, Patrick R, Horwitz P, Parkes M, Jenkins A, Massy C, Henderson-Wilson C, Arabena K. Exploring ecosystems and health by shifting to a regional focus: perspectives from the Oceania EcoHealth chapter. Int J Environ Res Public Health. 2015;12(10):12706–22.

    Article  PubMed  PubMed Central  Google Scholar 

  38. Kitikoon V, Sornmani S, Schneider CR. Studies on Tricula aperta and related taxa, the snail intermediate hosts of Schistosoma Mekongi. I. Geographical distribution and habitats. Malacol Rev. 1981;14(1):1.

    Google Scholar 

  39. Davis GM, Kitikoon V, Temcharoen P. Monograph on "Lithoglyphopsis" aperta, the snail host of Mekong River schistosomiasis. Malacologia. 1976;15(2):241–87.

    CAS  PubMed  Google Scholar 

  40. Katz N, Chaves A, Pellegrino J. A simple device for quantitative stool thick-smear technique in Schistosomiasis mansoni. Rev Inst Med Trop Sao Paulo. 1972;14(6):397–400.

    CAS  PubMed  Google Scholar 

  41. Enes JE, Wages AJ, Malone JB, Tesana S. Prevalence of Opisthorchis viverrini infection in the canine and feline hosts in three villages, Khon Kaen Province, northeastern Thailand. Southeast Asian J Trop Med Public Health. 2010;41(1):36–42.

    PubMed  PubMed Central  Google Scholar 

  42. Ebrahim A, El-Morshedy H, Omer E, El-Daly S, Barakat R. Evaluation of the Kato-Katz thick smear and formol ether sedimentation techniques for quantitative diagnosis of Schistosoma mansoni infection. Am J Trop Med Hyg. 1997;57(6):706–8.

    Article  CAS  PubMed  Google Scholar 

  43. Sri-Aroon P, Butraporn P, Limsoomboon J, Kaewpoolsri M, Chusongsang Y, Charoenjai P, Chusongsang P, Numnuan S, Kiatsiri S. Freshwater mollusks at designated areas in eleven provinces of Thailand according to the water resource development projects. Southeast Asian J Trop Med Public Health. 2007;38(2):294–301.

    PubMed  Google Scholar 

  44. Search FishBase: http://www.fishbase.org/search.php.

  45. http://fish.mongabay.com/data/Laos.htm.

  46. Steinmann P, Zhou XN, Li YL, Li HJ, Chen SR, Yang Z, Fan W, Jia TW, Li LH, Vounatsou P, et al. Helminth infections and risk factor analysis among residents in Eryuan county, Yunnan province. China Acta Trop. 2007;104(1):38–51.

    Article  PubMed  Google Scholar 

  47. Raso G, Utzinger J, Silue KD, Ouattara M, Yapi A, Toty A, Matthys B, Vounatsou P, Tanner M, N'Goran EK. Disparities in parasitic infections, perceived ill health and access to health care among poorer and less poor schoolchildren of rural cote d'Ivoire. Tropical Med Int Health. 2005;10(1):42–57.

    Article  Google Scholar 

  48. Maleewong W, Intapan P, Wongwajana S, Sitthithaworn P, Pipitgool V, Wongkham C, Daenseegaew W. Prevalence and intensity of Opisthorchis Viverrini in rural community near the Mekong River on the Thai-Laos border in northeast Thailand. J Med Assoc Thail. 1992;75(4):231–5.

    CAS  Google Scholar 

  49. Sayasone S, Odermatt P, Phoumindr N, Vongsaravane X, Sensombath V, Phetsouvanh R, Choulamany X, Strobel M. Epidemiology of Opisthorchis viverrini in a rural district of southern Lao PDR. Trans R Soc Trop Med Hyg. 2007;101(1):40–7.

    Article  PubMed  Google Scholar 

  50. Rim HJ, Sohn WM, Yong TS, Eom KS, Chai JY, Min DY, Lee SH, Hoang EH, Phommasack B, Insisengmay S: Fishborne trematode metacercariae detected in freshwater fish from Vientiane municipality and Savannakhet Province, Lao PDR. Korean J Parasitol 2008, 46(4):253-260. doi: 210.3347/kjp.2008.3346.3344.3253. Epub 2008 Dec 3320.

  51. Manivong K, Komalamisra C, Waikagul J, Radomyos P: Opisthorchis viverrini Metacercariae in Cyprinoid fish from three rivers in Khammouane Province, Lao PDR. J Trop Med Parasitol 2009, 32 (1):23-29.

  52. Rim HJ, Sohn WM, Yong TS, Eom KS, Chai JY, Min DY, Lee SH, Hoang EH, Phommasack B, Insisiengmay S. Fishborne trematode metacercariae in Luang Prabang, Khammouane, and Saravane Province, Lao PDR. Korean J Parasitol. 2013;51(1):107–14. 110.3347/kjp.2013.3351.3341.3107. Epub 2013 Feb 3318

    Article  PubMed  PubMed Central  Google Scholar 

  53. Chai JY, Darwin Murrell K, Lymbery AJ. Fish-borne parasitic zoonoses: status and issues. Int J Parasitol. 2005;35(11–12):1233–54.

    Article  PubMed  Google Scholar 

  54. Kiatsopit N, Sithithaworn P, Saijuntha W, Boonmars T, Tesana S, Sithithaworn J, Petney TN, Andrews RH. Exceptionally high prevalence of infection of Bithynia Siamensis goniomphalos with Opisthorchis viverrini cercariae in different wetlands in Thailand and Lao PDR. Am J Trop Med Hyg. 2012;86(3):464–9.

    Article  PubMed  PubMed Central  Google Scholar 

  55. Kiatsopit N, Sithithaworn P, Kopolrat K, Andrews RH, Petney TN. Seasonal cercarial emergence patterns of Opisthorchis viverrini infecting Bithynia Siamensis goniomphalos from Vientiane Province. Lao PDR Parasit Vectors. 2014;7(1):551.

    Article  PubMed  Google Scholar 

  56. Aunpromma S, Tangkawattana P, Papirom P, Kanjampa P, Tesana S, Sripa B, Tangkawattana S. High prevalence of Opisthorchis viverrini infection in reservoir hosts in four districts of Khon Kaen Province, an opisthorchiasis endemic area of Thailand. Parasitol Int. 2012;61(1):60–4. doi:10.1016/j.parint.2011.1008.1004. Epub 2011 Aug 1016

    Article  PubMed  Google Scholar 

  57. Kitikoon V, Schneider CR, Bhaibulaya M, Sittilerd S, Thirachantra S. Mekong schistosomiasis. 4. A parasitological survey of wild rodents, domestic pigs and cattle on Khong Island, Laos. Southeast Asian J Trop Med Public Health. 1975;6(2):223–9.

    CAS  PubMed  Google Scholar 

  58. Phongluxa K, Xayaseng V, Vonghachack Y, Akkhavong K, van Eeuwijk P, Odermatt P. Helminth infection in southern Laos: high prevalence and low awareness. Parasit Vectors. 2013;6(1):328. doi: 310.1186/1756-3305-1186-1328

    Article  PubMed  PubMed Central  Google Scholar 

  59. Lovis L, Mak TK, Phongluxa K, Aye Soukhathammavong P, Vonghachack Y, Keiser J, Vounatsou P, Tanner M, Hatz C, Utzinger J, et al. Efficacy of praziquantel against Schistosoma Mekongi and Opisthorchis Viverrini: a randomized, single-blinded dose-comparison trial. PLoS Negl Trop Dis. 2012;6(7):e1726.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  60. MoH. L: infectious and parasitic diseases, In: diagnosis and treatment in district hospitals, Ministry of Health Lao PDR. 2nd ed; 2004. p. 109–81.

    Google Scholar 

  61. Satoh M, Kokaze A. Treatment strategies in controlling strongyloidiasis. Expert Opin Pharmacother. 2004;5(11):2293–301.

    Article  CAS  PubMed  Google Scholar 

  62. Bisoffi Z, Buonfrate D, Angheben A, Boscolo M, Anselmi M, Marocco S, Monteiro G, Gobbo M, Bisoffi G, Gobbi F. Randomized clinical trial on Ivermectin versus Thiabendazole for the treatment of Strongyloidiasis. PLoS Negl Trop Dis. 2011;5(7):e1e254.

    Article  Google Scholar 

  63. Suputtamongkol Y, Premasathian N, Bhumimuang K, Waywa D, Nilganuwong S, Karuphong E, Anekthananon T, Wanachiwanawin D, Silpasakorn S. Efficacy and safety of single and double doses of ivermectin versus 7-day high dose albendazole for chronic strongyloidiasis. PLoS Negl Trop Dis. 2011;5(5):e1044.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

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Acknowledgements

We sincerely thank the population of the study villages and the authorities at the village, district and provincial departments for their active participation and their interest in the study. Furthermore, the support of the Centre of Malariology, Parasitology, and Entomology in Vientiane and in the province and districts is highly appreciated. We thank Mrs. Amena Briet for her efficient English editing.

Funding

We are grateful to the International Development Research Centre; Foreign Affairs, Trade and Development Canada (through the Global Health Research Initiative); and the Australian Agency for International Development for funding support.

Availability of data and materials

All datasets analysed during the current study are available from the corresponding author upon reasonable request.

Author information

Authors and Affiliations

  1. Swiss Tropical and Public Health Institute, Basel, Switzerland

    Youthanavanh Vonghachack & Peter Odermatt

  2. University of Basel, Basel, Switzerland

    Youthanavanh Vonghachack & Peter Odermatt

  3. Faculty of Basic Sciences, University of Health Sciences, Vientiane Capital, Lao PDR

    Youthanavanh Vonghachack

  4. Malariology, Parasitology and Entomology Station, Champasack province, Lao PDR

    Keoka Taisayyavong

  5. Provincial Health Department, Champasack province, Lao PDR

    Souphanh Phounsavath

  6. National Institute of Public Health, Ministry of Health, Vientiane Capital, Lao PDR

    Kongsap Akkhavong & Somphou Sayasone

Authors
  1. Youthanavanh Vonghachack
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  3. Keoka Taisayyavong
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  4. Souphanh Phounsavath
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  5. Kongsap Akkhavong
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  6. Somphou Sayasone
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Contributions

YV, PO, KA and SS designed the study; SS, YV, SP, KT implemented the study; YV, PO and SS analyzed and interpreted the data; YV wrote the first draft of the manuscript; PO and SS revised the manuscript. All authors read and approved the final version of the manuscript.

Corresponding author

Correspondence to Somphou Sayasone.

Ethics declarations

Ethics approval and consent to participate

This study was approved by the National Ethics Committee for Health Research, Ministry of Health (MOH), Vientiane, Lao PDR (reference no.043/NECR). Field activities were approved by the MOH steering committee. An inception meeting was organized at the study site prior to starting field work. Village and local health authorities and villagers were invited to participate in this meeting. Study participants were informed of the study aims and procedures, the benefits and risks of participating, as well as of their right to withdraw from the study at any time. Before enrolment, written informed consent was obtained from all study participants. For study participants under the age of 18, written informed consent was obtained from the parents or legal guardians. In addition, oral consent was obtained from each child participant between 12 and 17 years old. Permission to collect faecal samples from animals was obtained from their owners. All diagnosed infections were treated free of charge according to the Lao National guidelines [60]. Soil-transmitted helminths (STH) and/or trematode infections were treated with a single oral dose of 400 mg albendazole and praziquantel (40 mg/kg BW), respectively [60,61,62,63].

Consent for publication

A written, informed consent to share and disseminate data was obtained from all study participants before enrolment. For children aged below 18 years, the consent was obtained from their parent or legal guardian.

Competing interests

The authors declare that they have no competing interests.

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Vonghachack, Y., Odermatt, P., Taisayyavong, K. et al. Transmission of Opisthorchis viverrini, Schistosoma mekongi and soil-transmitted helminthes on the Mekong Islands, Southern Lao PDR. Infect Dis Poverty 6, 131 (2017). https://doi.org/10.1186/s40249-017-0343-x

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Keywords

Infectious Diseases of Poverty

ISSN: 2049-9957

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