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.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.

Prevalence and Risk Factors for Opisthorchis viverrini Infections in Upper Northeast Thailand

“…People who lived near canal, lake or river were 1.5 times more at risk of Opisthorchis infection than those who lived several kilometers away; due to disease vectors such as snails, their metacercania and the cyprinoid fish that they infect (Forrer et al, 2012). By contrast, Tesana et al (1991) discovered that even villages relatively from a river had higher infection(52.2%) than those nearer (24.7) (p<0.005).…”

Risk Factors for Opisthorchis viverrini and Minute Intestinal Fluke Infections in Lao PDR, 2009–2011

“…The Mekong River is a transboundary river in southeast Asia, and the estimated length is 4,350 km. 2 From the Tibetan Plateau, this river runs through China's Yunnan province, Burma (Myanmar), Lao PDR, Thailand, Cambodia, and Vietnam ( Figure 1). According to the 2005 census, the total population of Lao PDR was 5.62 million, of which 2.82 million were females and 2.80 million were males.…”

“…1 Specifically, O. viverrini and other fluke infections (i.e., minute intestinal flukes [MIFs] and the blood fluke Schistosoma mekongi) and soil-transmitted helminths are endemic. 2 The adult worm of O. viverrini inhabits the intra-and extrahepatic biliary system. The embryonated eggs containing a miracidium released from the gravid worm are discharged with the bile and eventually passed into environment in the fecal stream.…”

Global status of fish-borne zoonotic trematodiasis in humans

“…snails are normally present in water bodies. The absence of latrines and disposal of untreated faeces into the environment around villages constitutes an important factor responsible for the propagation of the parasite (Forrer et al 2012;Nithikethkul et al 2004;Sayasone et al 2007). The habit of people defecating on the ground in the bush not far from their houses, many of which are situated around the lakes, ponds, streams, etc., results in contamination of the water by the faeces containing O. viverrini eggs during the rainy season (Mas-Coma and Bargues 1997).…”