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Spatial ecology and transmission of a zoonotic helminth in Tibetan pastoralist communities
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Human alveolar echinococcosis (AE) is a rare but potentially fatal zoonotic disease across the northern hemisphere, caused by hepatic infection with the larval stage of the fox tapeworm Echinococcus multilocularis. It is endemic in areas of western China and our collaborative studies showed major human disease foci in south Gansu, south Ningxia and in Tibetan areas of northwest Sichuan, with ultrasound prevalences from <1->14%. Risk factors included dog ownership and proximity of deforested scrub/grass landscape habitats for susceptible small mammal reservoir host populations (microtines, ochotonids). In Tibetan pastoral communities semi-domestic parasite transmission involving dogs was described and modelled. Spatial variation in village AE rates was also linked to occurrence of optimal habitats for small mammals in overgrazed and fenced pastures. Anthropogenic induced heterogeneity in landscapes at local scales provided a metastable focus for sustainable transmission at regional scales across the eastern Tibetan Plateau. A spatial-deterministic model was developed that linked infection pressure to dogs (β) (based on purge, coproELISA and coproPCR) with the ratio of optimal/marginal habitats (ROMPA) of key small mammal species (based on spatial analyses of trapping data and activity indices). The model explains transmission heterogeneity in recent and past (archived satellite data) endemic landscapes, and is being applied across the Plateau to predict potential zones of transmission outside the current study sites
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