Spatial distribution of, and risk factors for, Opisthorchis viverrini infection in southern Lao PDR

Abstract

Background: Opisthorchis viverrini is a food-borne trematode species that might give rise to biliary diseases and the fatal cholangiocarcinoma. In Lao PDR, an estimated 2.5 million individuals are infected with O. viverrini, but epidemiological studies are scarce and the spatial distribution of infection remains to be determined. Our aim was to map the distribution of O. viverrini in southern Lao PDR, identify underlying risk factors, and predict the prevalence of O. viverrini at non-surveyed locations.

Methodology: A cross-sectional parasitological and questionnaire survey was carried out in 51 villages in Champasack province in the first half of 2007. Data on demography, socioeconomic status, water supply, sanitation, and behavior were combined with remotely sensed environmental data and fed into a geographical information system. Bayesian geostatistical models were employed to identify risk factors and to investigate the spatial pattern of O. viverrini infection. Bayesian kriging was utilized to predict infection risk at non-surveyed locations.

Principal findings: The prevalence of O. viverrini among 3,371 study participants with complete data records was 61.1%. Geostatistical models identified age, Lao Loum ethnic group, educational attainment, occupation (i.e., rice farmer, fisherman, and animal breeder), and unsafe drinking water source as risk factors for infection. History of praziquantel treatment, access to sanitation, and distance to freshwater bodies were found to be protective factors. Spatial patterns of O. viverrini were mainly governed by environmental factors with predictive modeling identifying two different risk profiles: low risk of O. viverrini in the mountains and high risk in the Mekong corridor.

Conclusions/significance: We present the first risk map of O. viverrini infection in Champasack province, which is important for spatial targeting of control efforts. Infection with O. viverrini appears to be strongly associated with exposure to the second intermediate host fish, human behavior and culture, whereas high transmission is sustained by the lack of sanitation.

Figure 1. Prevalence of O. viverrini infection in Champasack province, southern Lao PDR, stratified by age group.

Data were obtained from cross-sectional surveys carried out in 51 villages of Champasack province between January and May 2007.

Figure 2. Map of the predicted prevalence (median) of O. viverrini infection in Champasack province, southern Lao PDR.

Figure 3. Error coefficient of the predicted O. viverrini prevalence (a) and location-specific random effects (b).

The error coefficient is the ratio of the predicted prevalence median over its standard deviation (SD). Darker zones indicate higher uncertainty of the predictive model.

Figure 4. Lower (a) and upper estimates (b) of the predicted prevalence of O. viverrini infection in Champasack province, southern Lao PDR.

The lower and upper estimates pertain to the 2.5% and 97.5% confidence interval (CI), respectively.