Landscape, host diversity and functional invariants of Echinococcus multilocularis transmission: lessons from a study case
Résumé
The relative contribution of host communities combined with climate and landscape characteristics on non-vector-borne parasite transmission to humans has been a relatively neglected area of investigation. Based on a case study, we explore how landscape epidemiology and landscape ecology can contribute to better understand spatial and temporal processes of pathogen dynamics. Research carried out in different intermediate host communities of Western Europe and continental China indicate more intensive zoonotic transmission of the cestode E. multilocularis in homogeneous landscapes with larger areas of optimal habitats for one or some host species in low diversity small mammal communities, making multi-annual population outbreaks more likely. Retrospective analyses strongly suggest that increased transmission of E. multilocularis in the Jura massif, eastern France, and in China, even though habitats and species are different, originate from anthropogenic landscape alterations. Encouraged by the European agriculture common policy, farmers in the Doubs department, France, specialized in milk/cheese production in the 1960s and converted most tilled land into permanent grassland. With the destruction of hedges, this shifted the regional systems towards a more highly productive agriculture considering grass and triggered large scale small mammal outbreaks with a cascade of consequences in agriculture, biological conservation and public health. In China, similar effects came from deforestation and agriculture encroachments during the 1980s, extending areas favorable to small mammal intermediate host species prone to multiannual population outbreaks. This strongly suggests that functional invariants are at stake whatever the ecosystems, and that the impacts of landscape on community processes and population dynamics interfere with disease regulation and lead to more or less "healthy" landscapes. In such a context, disease transmission should be considered in a systems approach and taken into account together with other associated issues such as biodiversity, landscape management, small mammal pest control, conservation of protected species, game management, etc. Strong transdisciplinary research partnerships need to be forged to approach the research with the degree of creative thinking and comprehensiveness required by the nature of those system issues. Investigators must consider how they can integrate their findings into the social, economic, and political dialogue on both the ecosystems and health, on several scales.