HUMANS & BITHYNIA SNAILS: A HABITAT CONNECTIVITY STUDY OF THE DEFINITIVE AND FIRST INTERMEDIATE HOST OF OPISTHORCHIS VIVERRINI IN NORTHEAST THAILAND

Abstract

Disease transmission is an inherently spatial process, requiring host habitats to be functionally connected by landscape elements favourable for the circulation of vectors and hosts. Opisthorchis viverrini is a parasitic disease endemic to Northeast Thailand whose life cycle is closely associated with the water landscape. The lack of sewage treatment facilities in villages allow human faeces, where O. viverrini eggs are deposited, to be easily washed into the habitats of the first intermediate host, Bithynia snails. As a connected landscape facilitates the spread of pests or pathogen species, there is a need to consider the degree to which disease hosts habitats are connected for effective disease management. This study aims to provide a different perspective towards understanding the role of the landscape in O. viverrini transmission. Firstly, using structural (Euclidean distance) and functional connectivity (topological distance) measures, habitat connectivity between humans and Bithynia snails were examined. Pearson’s correlation revealed a negative relationship between faecal content (an indicator for potential snail infection) in snail habitats and the distance from human habitats. The statistically significant result for the topological distance measure highlights the importance of water in functionally promoting O. viverrini transmission. Sanitation improvement is hence essential to the eradication of the disease. Secondly, a landscape graph was constructed to understand the role of the landscape in facilitating (limiting) O. viverrini transmission. Landscape connectivity was quantified using two graph measures: mean node indegree and landscape components. Mean node indegree highlighted the potential for snail infection in a iii landscape where snail patches have high numbers of incoming connections. Landscape components revealed how mutually connected snail patches in a landscape can limit the spread of the disease.