Genetic Evidence for a Potential Environmental Pathway to Spillover Infection of Rat-Borne Leptospirosis.

In this study, we genotyped samples from environmental reservoirs (surface water and soil), colonized rat specimens, and cases of human severe leptospirosis from an endemic urban slum in Brazil, to determine the molecular epidemiology of pathogenic Leptospira and identify pathways of leptospirosis infection. We identified a well-established population of Leptospira interrogans serovar Copenhageni common to human leptospirosis cases, and animal and environmental reservoirs. This finding provides genetic evidence for a potential environmental spillover pathway for rat-borne leptospirosis through the environment in this urban community and highlights the importance of environmental and social interventions to reduce spillover infections.

Quantification of pathogenic Leptospira in the soils of a Brazilian urban slum.

BACKGROUND: Leptospirosis is an important zoonotic disease that causes considerable morbidity and mortality globally, primarily in residents of urban slums. While contact with contaminated water plays a critical role in the transmission of leptospirosis, little is known about the distribution and abundance of pathogenic Leptospira spp. in soil and the potential contribution of this source to human infection. METHODS/PRINCIPAL FINDINGS: We collected soil samples (n = 70) from three sites within an urban slum community endemic for leptospirosis in Salvador, Brazil. Using qPCR of Leptospira genes lipl32 and 16S rRNA, we quantified the pathogenic Leptospira load in each soil sample. lipl32 qPCR detected pathogenic Leptospira in 22 (31%) of 70 samples, though the median concentration among positive samples was low (median = 6 GEq/g; range: 4-4.31×102 GEq/g). We also observed heterogeneity in the distribution of pathogenic Leptospira at the fine spatial scale. However, when using 16S rRNA qPCR, we detected a higher proportion of Leptospira-positive samples (86%) and higher bacterial concentrations (median: 4.16×102 GEq/g; range: 4-2.58×104 GEq/g). Sequencing of the qPCR amplicons and qPCR analysis with all type Leptospira species revealed that the 16S rRNA qPCR detected not only pathogenic Leptospira but also intermediate species, although both methods excluded saprophytic Leptospira. No significant associations were identified between the presence of pathogenic Leptospira DNA and environmental characteristics (vegetation, rat activity, distance to an open sewer or a house, or soil clay content), though samples with higher soil moisture content showed higher prevalences. CONCLUSION/SIGNIFICANCE: This is the first study to successfully quantify the burden of pathogenic Leptospira in soil from an endemic region. Our results support the hypothesis that soil may be an under-recognized environmental reservoir contributing to transmission of pathogenic Leptospira in urban slums. Consequently, the role of soil should be considered when planning interventions aimed to reduce the burden of leptospirosis in these communities.

Impact of direct greenhouse gas emissions on the carbon footprint of water reclamation processes employing nitrification-denitrification.

Water reclamation has the potential to reduce water supply demands from aquifers and more energy-intensive water production methods (e.g., seawater desalination). However, water reclamation via biological nitrification-denitrification is also associated with the direct emission of the greenhouse gases (GHGs) CO2, N2O, and CH4. We quantified these direct emissions from the nitrification-denitrification reactors of a water reclamation plant in Southern California, and measured the (14)C content of the CO2 to distinguish between short- and long-lived carbon. The total emissions were 1.5 (±0.2) g-fossil CO2 m(-3) of wastewater treated, 0.5 (±0.1) g-CO2-eq of CH4 m(-3), and 1.8 (±0.5) g-CO2-eq of N2O m(-3), for a total of 3.9 (±0.5) g-CO2-eqm(-3). This demonstrated that water reclamation can be a source of GHGs from long lived carbon, and thus a candidate for GHG reduction credit. From the (14)C measurements, we found that between 11.4% and 15.1% of the CO2 directly emitted was derived from fossil sources, which challenges past assumptions that the direct CO2 emissions from water reclamation contain only modern carbon. A comparison of our direct emission measurements with estimates of indirect emissions from several water production methods, however, showed that the direct emissions from water reclamation constitute only a small fraction of the plant's total GHG footprint.