Conceived and designed the experiments: SS TKM JU PO. Performed the experiments: SS TKM MV OR KA. Analyzed the data: OR PV JU PO. Contributed reagents/materials/analysis tools: TKM. Wrote the paper: SS MV PV JU KA PO.
The authors have declared that no competing interests exist.
Detailed investigations of multiparasitism are scarce in the Mekong River basin. We assessed helminth (trematode, nematode, and cestode), and intestinal protozoa infections, and multiparasitism in random population samples from three different eco-epidemiological settings in Champasack province, southern Lao People's Democratic Republic (Lao PDR), and determined underlying risk factors.
Two stool samples were collected from 669 individuals aged ≥6 months over consecutive days and examined for helminth infections using the Kato-Katz method. Additionally, one stool sample per person was subjected to a formalin-ethyl acetate concentration technique for diagnosis of helminth and intestinal protozoa infections. Questionnaires were administered to obtain individual and household-level data pertaining to behavior, demography and socioeconomic status. Risk factors for hepato-biliary and intestinal parasitic infections and multiparasitism were determined using multiple logistic regressions analyses.
Multiple species intestinal parasite infections were common: 86.6% of the study participants harbored at least two and up to seven different parasites concurrently. Regarding nematode infections, hookworm was the most prevalent species (76.8%), followed by
There is a pressing need to intensify and sustain helminth control interventions in the southern part of Lao PDR. Given the high prevalence with nematode and trematode infections and the extent of multiparasitism, preventive chemotherapy is warranted. This intervention should be coupled with health education and improved access to clean water and adequate sanitation to consolidate morbidity control and enhance sustainability.
Multiparsitism is a general public health concern in tropical countries, and is of particular importance in the Mekong River basin of Southeast Asia. Here, we report results obtained from an in-depth study of hepato-biliary and intestinal multiparasitism and associated risk factors in three settings of the most southern province of Lao People's Democratic Republic. Multiple species intestinal parasite infections were very common: more than 80% of the study participants harbored at least two and up to seven different intestinal parasites concurrently. Of particular concerns are the high prevalence of the liver fluke
Lao People's Democratic Republic (Lao PDR) is a landlocked country situated in the Great Mekong sub-region of Southeast Asia, where socioeconomic and eco-epidemiological characteristics vary greatly according to location. In the northern part similar ecosystems are found as in southern People's Republic of China (P.R. China) with mountains and highlands dominating the landscapes. These topological features are natural barriers that might impede social and economic development, since transportation of commodities, communication and other exchanges are hampered. These issues exacerbate people's access to health care, clean water and adequate sanitation. Indeed, according to the results of the national population and housing census carried out in 2005, less than 20% and only about half of the population living in these areas had access to clean water and sanitation, respectively
The central and southern parts of Lao PDR are the low land along the Mekong River basin. In these regions, the socioeconomic conditions and means of communication and transport are more advanced than in northern Lao PDR. In recent years, through the formation of the ASEAN community, the economy of the Great Mekong sub-regions countries has been bolstered. Along with these changes and ecological transformations (e.g., deforestation and water resources developments), particularly in the lowlands of the Mekong River basin, patterns of parasitic infections are changing
The present study was carried out in different eco-epidemiological settings of Champasack province, southern Lao PDR. Using a cross-sectional design, the purpose was to assess the prevalence and intensity of hepato-biliary and intestinal parasitic infections and intestinal multiparasitism, and to identify underlying risk factors.
The study was carried out in three distinct eco-epidemiological settings of Champasack province (
Khong district (estimated population: 80,000)
The Mounlapamok district is also located in the southern part of the province (∼80 km from Pakse city) with an estimated population of 40,000
Paksong district is located on the Bolovan plateau (geographical coordinates: 14.58°–15.23° N and 105.55°–106.48° E) at an elevation of ∼1,000 m above sea level in the northeast of the province (∼50 km from Pakse city). It is a mountainous area with an estimated population of 65,000
The study was approved by the Ethics Committee in Basel, Switzerland (EKBB; reference no. 255/06) and the National Ethics Committee, Ministry of Health (MoH) in Vientiane, Lao PDR (reference no. 027/NECHR). Permission for field work was obtained from MoH, the Provincial Health Office (PHO) and the District Health Office (DHO). Village meetings were held and village authorities and villagers were given detailed explanations about the aims, procedures, potential risks and benefit of the study. An information sheet in the local language was read aloud to all household members and their questions answered. Individual oral consent was obtained from all adult household members (literacy is very low in this part of Lao PDR, and hence we opted for oral rather than written consent). However, written informed consent was obtained from all heads of households. A witness observing this procedure also signed the consent form.
All individuals infected with
Our cross-sectional surveys were carried out between March and May 2006. In each setting, three villages were selected from the available village list in collaboration with the DHO, and 20–25 households were randomly selected in each village. All household members aged ≥6 months were invited to participate. The number of inhabitants per household was recorded. Unique identifiers were assigned to households and study participants.
In each village, a house (usually a school or a temple) was designated as an area of work for Kato-Katz (KK) thick smear preparation, microscopic examination of stool samples, etc. Two members of our research team (one interviewer and one general physician) went from house to house and interviewed first the head of household and then the remaining household members. Two questionnaires were administrated in each household. The household questionnaire (after pre-testing in a neighboring area) was administered to the heads of household. Data pertaining to household characteristics (e.g., building type and water supply), asset ownership (e.g., farm engine and bicycle) and ownership of animals (e.g., buffalo and cow) were collected. The geographical coordinates of each household were obtained by using a hand-held global positioning system (GPS) receiver (Garmin Ltd., Olathe, USA). Next, a pre-tested individual questionnaire was used and all household members were interviewed for demographic data (e.g., age, sex, educational attainment, and professional activity) and behavioral risks (e.g., food consumption habits and personal hygiene). Parents or legal caregivers answered for children.
Finally, stool containers were prepared for all members of each study household. Participants' names and unique identifiers were marked on the containers and distributed to the heads of household with detailed instructions of how to collect a fresh morning stool sample. All study participants were asked to provide a sufficiently large stool sample (at least 5 g) so that both KK and the formalin-ethyl acetate concentration technique (FECT) could be performed. After filled containers were collected, new empty containers were handed out with the goal to obtain three stool samples from each participant over consecutive days.
Stool samples were processed in the designated area of work in the study village within a maximum of 2 hours after collection by experienced laboratory technicians. A single KK thick smear was prepared from each stool sample, using a standard plastic template holding 41.7 mg of stool
Additionally, exactly 300 mg of stool taken from one sample was fixed in a tube containing 10 ml of sodium acetate acetic-acid formalin (SAF)
Data were double-entered and cross-checked using EpiData version 3.1 (Epidata Association; Odense, Denmark). Statistical analyses were performed with STATA version 10 (Stata Corporation; College Station, TX, USA). Only those individuals who had at least two KK thick smear readings and an additional FECT result, and complete questionnaire data were included in the final analyses.
People's socioeconomic status was estimated using a household-based asset approach and the population was stratified into wealth quintiles, namely (i) poorest, (ii) very poor, (iii) poor, (iv) less poor, and (v) least poor. Wealth quintiles were constructed using principal component analysis (PCA), as proposed by the Health Nutrition and Population/World Bank in 2000
Point prevalence of parasitic infections were determined and stratified by study area, sex, and age group. A chi-square (χ2) test was employed to investigate associations between categorical variables (e.g., between infection status and sex, age group, and study area). Study participants were subdivided into five age groups, namely (i) <5 years, (ii) 6–15 years, (iii) 16–30 years, (iv) 31–55 years, and (v) >55 years. The intensity of helminth egg counts was expressed as eggs per gram of stool (EPG). Intensity rate ratio (IRR) of EPG was calculated using negative binomial regression models and associated with sex and age groups. A predictor variable with level of significance below 0.15 in the bivariate logistic regression models was included in the multiple logistic regressions to investigate the associations between the parasitic infections and a particular risk factor. Random effect models were fitted into all regressions, taking into account the random effect of households.
From 1,213 enrolled participants, 1,051 were present during the cross-sectional survey and responded to our questionnaire (
Among this cohort, 212 individuals (31.7%) were from Paksong district, 232 (34.7%) from Mounlapamok district, and 225 (33.6%) from Khong district. Most study participants belonged to the Lao-loum ethnic groups (68.5%), whereas the Lao-theung minority accounted for the remaining 31.5%. There were slightly more females (n = 347, 51.9%). The median age was 15 years (range: 6 months to 87 years). Age structure was as follows: ≤5 years (17.3%), 6–15 years (32.9%), 16–30 years (16.4%), 31–55 years (24.9%) and >55 years (8.4%). Adults were primarily engaged in subsistence farming (52.1%), while there were only few government employees (1.4%). No professional activity accounted for 46.5% of the study participants. Of those, 17.3%, 20.4% and 8.8% were preschool-aged children, pupils or students and elderly persons, respectively.
With regard to wealth, we observed that most study participants from Paksong district belonged to the poorest group (53.5%), whereas none of them were classified into the group of the least poor. In Khong and Mounlapamok districts, the combined percentage of less poor and least poor was 40.4% and 29.3%, respectively. Only a few individuals (Mounlapamok: 3.0% and Khong: 2.2%) belonged to the poorest group (
Parasites | Prevalence (95% CI) | Study settings | Sex | Age groups (years) | |||||||
(n = 669) | Khong (n = 225) | Mounlapamok (n = 232) | Paksong (n = 212) | Female (n = 347) | Male (n = 322) | ≤5 (n = 116) | 6–15 (n = 220) | 16–30 (n = 110) | 31–55 (n = 167) | >55 (n = 56) | |
64.3 (60.6–67.9) | 92.0 | 90.9 | 5.7 |
65.1 | 63.4 | 44.0 | 64.6 | 69.1 | 70.1 | 78.6 | |
24.2 (21.0–27.5) | 68.0 | 3.9 | 0.0 |
24.2 | 24.2 | 9.9 | 30.0 | 15.4 | 22.2 | 32.1 | |
6.0 (4.2–7.8) | 12.9 | 4.7 | 0.0 |
6.1 | 5.9 | 3.5 | 4.6 | 4.6 | 5.4 | 5.4 | |
Hookworm | 76.8 (73.6–80.0) | 71.1 | 66.0 | 94.8 |
76.7 | 77.0 | 39.7 | 80.0 | 31.8 | 78.4 | 75.0 |
31.7 (28.2–35.2) | 7.1 | 6.0 | 85.9 |
31.7 | 31.7 | 39.7 | 31.8 | 31.8 | 29.9 | 23.2 | |
25.0 (21.7–28.3) | 13.3 | 8.2 | 55.7 |
23.6 | 26.4 | 19.0 | 26.4 | 26.4 | 25.2 | 14.3 | |
4.6 (3.0–6.0) | 9.8 | 3.9 | 0.0 |
14.9 | 4.4 | 4.3 | 1.8 | 1.8 | 7.8 | 5.4 | |
3.6 (2.2–5.0) | 3.1 | 4.4 | 3.3 | 5.2 | 1.9 |
2.6 | 2.7 | 3.6 | 3.6 | 8.9 | |
3.7 (2.3–5.2) | 1.8 | 4.3 | 5.2 | 3.1 | 4.7 | 0.9 | 2.7 | 3.6 | 6.0 | 7.1 | |
2.7 (1.5–3.9) | 0.0 | 0.0 | 8.5 |
2.9 | 2.5 | 1.7 | 2.3 | 2.7 | 3.6 | 3.6 | |
0.5 (<0.1–0.9) | 0.5 | 0.9 | 0.0 | 0.6 | 0.3 | 0.9 | 0.5 | 0.9 | 0.0 | 0.0 | |
13.6 (11.0–16.2) | 19.6 | 6.5 | 15.1 |
13.0 | 14.3 | 7.8 | 15.0 | 13.6 | 15.0 | 16.1 | |
7.2 (5.2–9.1) | 3.0 | 8.4 | 10.4 |
7.8 | 6.5 | 6.0 | 7.3 | 9.1 | 4.8 | 12.5 | |
4.9 (3.3–6.6) | 3.0 | 5.9 | 6.1 | 2.6 | 7.6 |
5.2 | 6.4 | 8.2 | 1.8 | 1.8 | |
0.6 (<0.1–1.2) | 0.6 | 0.4 | 0.5 | 0.3 | 0.9 | 0.9 | 0.9 | 0.0 | 0.6 | 0.0 |
CI, confidence interval.
*
**
The overall infection prevalence of hookworm,
Cestode infections such as
Hookworm | ||||||||||
IRR (95% CI) | IRR (95% CI) | IRR (95% CI) | IRR (95% CI) | IRR (95% CI) | ||||||
Female | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | |||||
Male | 0.92 (0.76–1.11) | 0.404 | 1.18 (0.85–1.64) | 0.308 | 1.08 (0.93–1.25) | 0.321 | 0.96 (0.81–1.12) | 0.593 | 0.91 (0.72–1.16) | 0.437 |
≤ 5 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | |||||
6–15 | 2.95 (2.08–4.19) | 1.79 (1.01–3.18) | 1.49 (1.17–1.90) | 1.25 (0.98–1.61) | 1.10 (0.74––1.64) | |||||
16–30 | 5.37 (3.68–7.84) | 1.39 (0.72–2.68) | 1.30 (0.99–1.69) | 0.85 (0.63–1.13) | 0.98 (0.63–1.54) | |||||
31–55 | 7.18 (5.01–10.29) | 1.06 (0.57–1.96) | 1.16 (0.90–1.50) | 1.09 (0.84–1.42) | 0.88 (0.58–1.34) | |||||
>55 | 7.41 (4.82–11.42) | <0.001 | 1.30 (0.63–2.67) | 0.102 | 1.19 (0.85–1.67) | 0.008 | 0.81 (0.55–1.19) | 0.170 | 1.29 (0.66–2.53) | 0.605 |
CI, confidence interval; IRR, intensity rate ratio.
Only 13 (1.9%) individuals were free of intestinal parasites. Mono-infections were observed in 77 individuals (11.5%). Hence, most of the study participants had a multiple species intestinal parasite infection: 32.9% were infected with two different parasites, 53.5% harbored 3–6 parasite species concurrently, and in one individual seven different parasites were observed. Over a third of the study participants living in Paksong and Khong districts were infected with three different parasite species concurrently and almost half of the surveyed Mounlapamok residents were concurrently infected with at least two parasite species (
Association | OR (95% CI) | ||
5.09 (2.49–10.42) | <0.001 | ||
0.05 (0.03–0.07) | <0.001 | ||
0.34 (0.20–0.58) | <0.001 | ||
5.64 (2.75–11.56) | <0.001 | ||
3.19 (1.58–6.45) | 0.001 | ||
2.19 (1.26–3.79) | 0.005 | ||
2.20 (1.01–4.83) | 0.049 | ||
2.07 (1.55–11.03) | 0.005 | ||
Hookworm | 1.70 (1.04–2.79) | 0.034 | |
10.64 (4.29–26.36) | <0.001 | ||
5.68 (2.32–13.87) | <0.001 | ||
Hookworm | 3.52 (3.64–19.05) | <0.001 | |
3.51 (1.33–9.26) | 0.011 | ||
2.52 (1.45–4.39) | 0.001 | ||
0.05 (0.03–0.08) | <0.001 | ||
2.55 (1.50–4.34) | 0.001 | ||
Hookworm | 2.38 (2.17–12.76) | <0.001 | |
4.59 (1.24–16.99) | 0.022 | ||
4.09 (1.61–10.36) | 0.003 | ||
2.61 (1.11–6.15) | 0.028 | ||
0.08 (0.18–0.51) | <0.001 | ||
4.03 (1.24–13.02) | 0.020 | ||
8.60 (2.23–33.23) | 0.002 | ||
4.29 (1.15–15.90) | 0.030 | ||
3.40 (1.52–7.62) | 0.003 | ||
19.69 (2.59–149.61) | 0.004 | ||
2.19 (1.26–3.80) | 0.005 | ||
3.78 (1.93–7.38) | <0.001 | ||
0.59 (0.35–0.99) | 0.044 | ||
2.57 (1.23–5.37) | 0.012 | ||
3.91 (1.94–7.90) | <0.001 | ||
4.14 (1.26–13.61) | <0.019 | ||
4.03 (2.05–7.92) | <0.001 | ||
2.69 (1.21–6.00) | 0.016 |
More than half of our fully compliant study participants (n = 345, 51.6%) reported to have consumed at least once raw fish dishes within 7 days prior to the interview. The habit of raw fish consumption was particularly frequent among the Lao-loum ethnic group (85.7%), and significantly less common among the Lao-theung ethnic group (14.3%; LRT = 98.04, P <0.001). Consumption of raw meat dishes was reported by 12.3% of our study population. Of those, 80.7% belonged to the Lao-loum and 19.3% to the Lao-theung ethnic group.
Indicators | Crude OR (95%CI) | Adjusted OR (95% CI) | ||
Age group (in year) | ||||
< 5 | 1.00 | - --- | 1.00 | - --- |
6–15 | 5.64 (2.10–15.13) | 3.99 (1.93–8.24) | ||
16–30 | 19.49 (5.53–68.67) | 17.5 (5.70–53.68) | ||
31–55 | 19.93 (5.97–66.51) | 12.30 (4.68–32.29) | ||
>55 | 49.74 (8.00–309.04) | <0.001 | 13.96 (3.32–58.75) | <0.001 |
Ethnic groups | ||||
Not Laoloum | 1.00 | 1.00 | - --- | |
Laoloum | 154.9 (81.20–295.70) | <0.001 | 303.45 (134.20–686.63) | <0.001 |
Daily bathing in Mekhong River | ||||
No | 1.00 | 1.00 | - --- | |
Yes | 19.50 (8.87–42.87) | <0.001 | 3.20 (1.84–5.83) | <0.001 |
Age group (in year) | ||||
< 5 | 1.00 | - --- | 1.00 | - --- |
6–15 | 2.32 (1.24–4.34) | 2.21 (1.28–3.80) | ||
16–30 | 2.51 (1.23–5.14) | 2.22 (1.16–4.23) | ||
31–55 | 2.39 (1.24–4.62) | 2.10 (1.18–3.72) | 0.011 | |
>55 | 2.26 (1.01–5.50) | 0.040 | N.A. | N.S. |
Ethnic groups | ||||
Not Laoloum | 1.00 | - --- | 1.00 | - --- |
Laoloum | 0.11 (0.05–0.23) | <0.001 | 0.12 (0.07–0.23) | <0.001 |
Socio-economic status | ||||
Least poor | 1.00 | - --- | 1.00 | - --- |
Less poor | 0.35 (0.06–2.10) | N.A. | ||
Poor | 1.27 (0.26–6.11) | N.A. | ||
Very poor | 50.14 (10.39–241.97) | N.A. | ||
Most poor | 226.73 (41.64–434.43) | <0.001 | 3.53 (1.47–8.47) | 0.010 |
Report of eating any raw foodstuffs a week prior to survey (e.g., meat, fish, and vegetables) | ||||
No | 1.00 | 1.00 | - --- | |
Yes | 2.12 (1.15–3.90) | 0.021 | 2.74 (1.44–5.20) | 0.002 |
CI, confidence interval; N.S., not significant; N.A., not applicable; OR, odds ratio.
Helminth infections are widespread in Lao PDR and the Great Mekong sub-region in general.
Our data confirm that multiple species intestinal parasite infections are the norm rather than the exception; indeed more than 4 out of 5 study participants with complete data records harbored at least two different species concurrently, and several intestinal parasite species were found at high prevalence rates. Worryingly,
Limitations of our study are as follows. First, although we employed a rigorous diagnostic approach, the ‘true’ extent of multiparasitism is still underestimated. The diagnostic techniques used in our study only have a low sensitivity for the detection of certain parasite species (e.g.,
Highest infection intensities of
The high prevalence of
Our findings underscore that intestinal multiparasitism is common throughout Champasack province. The same observations have been made in other parts of Lao PDR
From a clinical point of view, co-infection of
Another interesting finding of our study was the significant association observed between
Soil-transmitted helminths were also found to be highly prevalent in the present study, particularly among those living in the highlands of Paksong district. An infection with soil-transmitted helminths can lead to nutritional deficiencies and may impair growth and cognitive development in children
Epidemiologic studies have shown that prevalence and intensity of several parasitic infections are governed by behavioral, socioeconomic, and environmental characteristics
Finally, we found a low prevalence of intestinal protozoa in our study cohort. These findings support the previous observations, which have shown low prevalence of pathogenic intestinal protozoa in Southeast Asia
We conclude that multiparasitism is the rule in different eco-epidemiological settings of Champasack province, and most likely elsewhere in Lao PDR. The extent of multiparasitism and the high infection prevalence and intensity with a host of intestinal parasites, most importantly
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We are grateful for the active participation of the people in the Khong, Mounlapamok, and Paksong districts, and the support of the curative and preventive health authorities of the various locations. We acknowledge the support of Professor Marcel Tanner, Director of the Swiss Tropical and Public Health Institute and Mrs. Isabelle Grilli who helped with the stool sample examinations.