Seeking the environmental source of Leptospirosis reveals durable bacterial viability in river soils

Abstract

BackgroundLeptospirosis is an important re-emerging infectious disease that affects humans worldwide. Infection occurs from indirect environment-mediated exposure to pathogenic leptospires through contaminated watered environments. The ability of pathogenic leptospires to persist in the aqueous environment is a key factor in transmission to new hosts. Hence, an effort was made to detect pathogenic leptospires in complex environmental samples, to genotype positive samples and to assess leptospiral viability over time.Methodology/Principal findingsWe focused our study on human leptospirosis cases infected with the New Caledonian Leptospira interrogans serovar Pyrogenes. Epidemiologically related to freshwater contaminations, this strain is responsible for ca. 25% of human cases in New Caledonia. We screened soil and water samples retrieved from suspected environmental infection sites for the pathogen-specific leptospiral gene lipL-32. Soil samples from all suspected infection sites tested showed detectable levels of pathogenic leptospiral DNA. More importantly, we demonstrated by viability qPCR that those pathogenic leptospires were viable and persisted in infection sites for several weeks after the index contamination event. Further, molecular phylogenetic analyses of the leptospiral lfb-1 gene successfully linked the identity of environmental Leptospira to the corresponding human-infecting strain.Conclusions/SignificanceAltogether, this study illustrates the potential of quantitative viability-PCR assay for the rapid detection of viable leptospires in environmental samples, which might open avenues to strategies aimed at assessing environmental risk.

A systematic review of Leptospira in water and soil environments

“…PCR methods have successfully been combined with the use of propidium monoazide to dramatically reduce the detection of dead or membrane-compromised cells. This technique, known as viability-PCR, provides indications about Leptospira viability in environmental samples [13,19]. Recently, some researchers have optimized procedures for the molecular detection of pathogenic leptospires from environmental waters [64], increasing possibilities for further studies on environmental leptospirosis and opening avenues for real One Health studies of this complex zoonosis.…”

“…Transmission can occur by contact between wounded skin or mucosae and contaminated soil or water. Leptospirosis had long been known as an environment-borne infection, even before its etiological agent could be identified [5] and the term of "environmental reservoir" of leptospirosis has been proposed for soils in endemic regions [5][6][7][8][9][10][11][12][13][14][15]. Consequently, studies have focused on source investigations and on environmental risk factors to understand interspecies contaminations [16].…”

A Live Attenuated Vaccine Model Confers Cross-Protective Immunity Against Different Species ofLeptospiraspp.

“…Currently the Leptospir a genus comprises 64 species with more than 300 serovars, with 17 of those species containing strains that can potentially cause severe disease in humans and animals 4,5 . A broad range of mammalian reservoirs harbor the spirochete in their renal tubules shedding the bacteria in their urine for long periods of time 6,7 . Leptospirosis is an environmentally-transmitted disease, for which the primary mode of transmission to humans is through contact with contaminated water or soil 8 .…”

“…Until recently, the inability to produce well-defined mutants has preempted efforts to identify a safe and efficacious attenuated vaccine. However, current advances in genomic tools and whole-genome sequencing data for Leptospira 1,6 have circumvented this limitation and some promising results have been shown 15,16 .…”

An Ecological Framework for Modeling the Geography of Disease Transmission

“…Parasite life cycles range from having free-living stages to being completely restricted within a host. Leptospira bacteria (the causative agent of leptospirosis) are capable of persisting in humid soils and waterlogged environments [57]. In this case, environmental variables such as precipitation or the presence of seasonal water bodies are more likely to have direct effects.…”