Spatial Distribution of, and Risk Factors for, Opisthorchis viverrini Infection in Southern Lao PDR

BackgroundOpisthorchis 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. MethodologyA 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 FindingsThe 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/SignificanceWe 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.

背景：麝猫后睾吸虫（Opisthorchis viverrini）是一种食源性吸虫，可引发胆道疾病乃至致命的胆管癌。在老挝人民民主共和国（Lao PDR），估计有250万人感染O. viverrini，但相关流行病学研究相对匮乏，感染的空间分布仍有待明确。本研究旨在绘制老挝南部地区O. viverrini的感染分布图谱，识别潜在危险因素，并预测未调查区域的感染流行率。

研究方法：2007年上半年，研究团队在占巴塞省的51个村庄开展了横断面寄生虫学与问卷调查。将人口统计学特征、社会经济状况、供水情况、卫生设施条件及行为相关数据与遥感环境数据相结合，导入地理信息系统（Geographical Information System, GIS）。采用贝叶斯地统计模型（Bayesian geostatistical models）识别感染危险因素，并探究O. viverrini感染的空间分布模式；利用贝叶斯克里金法（Bayesian kriging）预测未调查区域的感染风险。

主要研究结果：在3371名拥有完整数据记录的研究参与者中，O. viverrini的感染率为61.1%。地统计模型识别出年龄、老龙族（Lao Loum）族群、受教育程度、职业（即稻农、渔民与畜牧者）以及不安全饮用水源为感染危险因素；吡喹酮治疗史、卫生设施可及性以及与淡水水体的距离则为保护因素。O. viverrini的空间分布格局主要受环境因素调控，预测模型识别出两类不同的风险特征：山区感染风险较低，湄公河走廊（Mekong corridor）感染风险较高。

结论与意义：本研究首次绘制了占巴塞省O. viverrini感染的风险图谱，这对精准开展防控工作具有重要指导价值。O. viverrini感染似乎与第二中间宿主鱼类的接触、人类行为及文化密切相关，而卫生设施的缺失则维持了高传播水平。