Leptospirosis in Rio Grande do Sul, Brazil: An Ecosystem Approach in the Animal-Human Interface

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Abstract
Leptospirosis is an epidemic-prone neglected disease that affects humans and animals, mostly in vulnerable populations. The One Health approach is a recommended strategy to identify drivers of the disease and plan for its prevention and control. In that context, the aim of this study was to analyze the distribution of human cases of leptospirosis in the State of Rio Grande do Sul, Brazil, and to explore possible drivers. Additionally, it sought to provide further evidence to support interventions and to identify hypotheses for new research at the human-animal-ecosystem interface. The risk for human infection was described in relation to environmental, socioeconomic, and livestock variables. This ecological study used aggregated data by municipality (all 496). Data were extracted from secondary, publicly available sources. Thematic maps were constructed and univariate analysis performed for all variables. Negative binomial regression was used for multivariable statistical analysis of leptospirosis cases. An annual average of 428 human cases of leptospirosis was reported in the state from 2008 to 2012. The cumulative incidence in rural populations was eight times higher than in urban populations. Variables significantly associated with leptospirosis cases in the final model were: Parana/Paraiba ecoregion (RR: 2.25; CI95%: 2.03–2.49); Neossolo Litolítico soil (RR: 1.93; CI95%: 1.26–2.96); and, to a lesser extent, the production of tobacco (RR: 1.10; CI95%: 1.09–1.11) and rice (RR: 1.003; CI95%: 1.002–1.04). Urban cases were concentrated in the capital and rural cases in a specific ecoregion. The major drivers identified in this study were related to environmental and production processes that are permanent features of the state. This study contributes to the basic knowledge on leptospirosis distribution and drivers in the state and encourages a comprehensive approach to address the disease in the animal-human-ecosystem interface. Leptospirosis is a bacterial disease affecting humans and several animal species, which serve as reservoirs for infection. Contamination happens through exposure to urine of infected animals in water and soil. A better understanding of the factors that affect the transmission of the disease, incorporating the relationship between humans, animals, and ecosystems within the One Health approach, would allow for tailored prevention and control measures at the local level. The aims of this study were to analyze the distribution of leptospirosis human cases and the possible factors that influence the transmission of the disease in the state of Rio Grande do Sul, as well as provide evidence to support the development of interventions and guide new studies in the region. Leptospirosis cases and possible environmental, socioeconomic, and livestock factors were analyzed. The study used data by municipality (all 496) obtained via an open access database. Georeferenced maps were constructed and statistical analysis performed for 26 variables. A multivariable regression analysis was carried out. An annual average of 428 human cases of leptospirosis was reported in the state from 2008 to 2012. The cumulative incidence in rural populations was eight times higher than in urban populations. Variables significantly associated with leptospirosis cases in the final model were: ecoregion, type of soil and to a lesser extent tobacco and rice production. Results showed that leptospirosis cases were concentrated in the state capital and in specific ecoregions. Environmental and agricultural production processes were identified as possible risk factors and these conditions are probably permanent characteristics of the state. This study contributes to the knowledge on leptospirosis distribution and risk factors in the state, and also highlights the importance of a holistic view and intersectoral approach in preventing the disease.

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