Soils, rainfall and leptospirosis – SPIraL

Leptospirosis is a severe bacterial disease with highest impact in the Tropics. Recent data show a growing incidence in Europe (France, Belgium, Croatia, the Netherlands). Leptospirosis affects 1 million humans yearly, killing 58,900, but remains neglected and attracts insufficient attention. One century ago, Noguchi outlined its epidemiology and pointed the role of the survival of leptospires “in nature”. Leptospires chronically colonize the kidneys of mammals and are shed in the environment, where humans get infected. Animal-environment-human interactions determine patterns of disease; thus understanding the ecology of leptospires in ecosystems is critical. Yet, leptospirosis has mostly been studied as a zoonosis; environmental determinants of transmission have not been an active field of research. Early work identified conditions for Leptospira survival; however, recent work show that assumptions need be revisited. It is assumed that pathogens only survive in soil or freshwater; yet no resistance form was ever evidenced. The ability of the environment to support the survival of leptospires is a cornerstone of leptospirosis epidemiology.
SpIRAL aims at filling the gaps in knowledge of Leptospira habitat outside a host. SpIRAL goals are to (1) identify the environmental abiotic factors that impact Leptospira survival in soils and freshwater, (2) characterize the microbiota that shelter Leptospira in the environment (3) model the dynamics of Leptospira dispersion upon rainfall and (4) generate a spatial map of leptospirosis risk integrating environmental, ecological and climatic parameters. This holistic approach of the environmental component of leptospirosis will yield new knowledge and avenues for a better control of the disease, also making the case for other environment-borne infections.
SpIRAL will take benefit of the expertise developed in New Caledonia in the fields of leptospirosis and soil sciences. A full knowledge of Leptospira environmental habitats will be acquired, requiring a substantial amount of information on the ecosystems allowing or oppositely impairing their viability. First a collection of georeferenced soils and sediments will be collected and characterized (physical and chemical soil analysis, presence of virulent leptospires in situ, prokaryotic and eukaryotic microbiota). Their ability to support the survival of Leptospira will be assessed in vitro using microcosms. The interaction of pathogenic leptospires with soil particles, with Free-Living Ameoba or in natural biofilms will also be studied, providing further insight into their environmental lifestyle. Taking benefit of a site fully equipped for hydrology, we will also study and model the dispersion of Leptospira during rainfalls, known triggers of leptospirosis outbreaks. The model will be established in the pilot watershed then evaluated in other areas of high incidence. The information gained on Leptospira dynamics in water under the influence of rain will prove for prevention. Data of SpIRAL together with known leptospirosis risk factors will be analyzed spatially to establish and evaluate a spatial map of disease risk. This model will be used to study the relative weights of risk factors and to translate research findings into health benefits.
SpIRAL aims to provide a comprehensive understanding of the ecosystem in the persistence of- and dynamics of exposure to- leptospirosis. It will address knowledge gaps on basic aspects of Leptospira lifestyle outside a host, key determinants of human disease, and will provide an integrated, data-rich and comprehensive and generalizable picture of Leptospira environmental habitat. Shifting the paradigm of leptospirosis epidemiology from a zoonosis to an environment-borne infection, SpIRAL aims to better understand epidemiology and infer risk management strategies for a better control of the disease.