Fish sharing as a risk factor for Opisthorchis viverrini infection: evidence from two villages in north-eastern Thailand

Background: Foodborne trematodiasis (FBT) is a significant global health problem, with the liver flukes Opisthorchis viverrini, O. felineus, and Clonorchis sinensis contributing to half of the global burden of FBT. North-eastern Thailand where O. viverrini is endemic and un-cooked fish dishes remain an integral part of the food culture has the highest reported incidence of opisthorchiasis, including associated cholangiocarcinoma. Both food sharing and eating practices are potentially important factors in FTB, suggesting an important role for the social ecology of disease transmission in these rural communities. Methods: Two rural Thai-Lao villages that were part of a 12-village project in Northeastern Thailand were selected for detailed investigation of O. viverrini infection risk associated with sharing of raw fish dishes among households. The project included screening individuals for infection and cholangiocarcinoma, a household questionnaire, and offering treatment options for positive individuals. Social network mapping was used to construct raw fish dish-sharing networks and create a proxy variable capturing variability in the degree of food sharing (DFS), measured as the number of different households with which each household shared fish dishes. Measures of associations between DFS, O. viverrini infection, the frequency of raw fish consumption, and the number of raw fish dishes consumed were generated using binary logistic regression, proportional odds ordinal logistic regression, and Poisson regression. Results: The results showed that the probability that a household has members infected with O. viverrini increased by similar to 7% (P < 0.01) for each additional household included in its network. Moreover, the frequency and number of types of raw fish dishes consumed increased significantly as the DFS increased. Of the two villages, that with the highest infection prevalence (48% versus 34.6%) had significantly higher social connectivity overall (P < 0.001). Conclusions: Our findings suggest that the social ecology of human settlements may be key to understanding the transmission dynamics of some FBT. In the case of O. viverrini in Thai-Lao communities, for which food sharing is a traditional practice supporting social cohesion, food sharing network mapping should be incorporated into community-based interventions. These should encourage fish dish preparation methods that minimize infection risk by targeting households with high DFS values.