Spatial and temporal dynamics of pathogenic Leptospira in surface waters from the urban slum environment

Abstract

Leptospirosis has emerged as an important urban health problem as slum settlements have expanded worldwide. Yet the dynamics of the environmentally transmitted Leptospira pathogen has not been well characterized in these settings. We used a stratified dense sampling scheme to study the dynamics of Leptospira abundance in surface waters from a Brazilian urban slum community. We collected surface water samples during the dry, intermediate and rainy seasons within a seven-month period and quantified pathogenic Leptospira by quantitative PCR (qPCR). We used logistic and linear mixed models to identify factors that explained variation for the presence and concentration of Leptospira DNA. Among 335 sewage and 250 standing water samples, Leptospira DNA were detected in 36% and 34%, respectively. Among the 236 samples with positive results geometric mean Leptospira concentrations were 152 GEq/mL. The probability of finding Leptospira DNA was higher in sewage samples collected during the rainy season when increased leptospirosis incidence occurred, than during the dry season (47.2% vs 12.5%, respectively, p = 0.0002). There was a marked spatial and temporal heterogeneity in Leptospira DNA distribution, for which type of water, elevation, and time of day that samples were collected, in addition to season, were significant predictors. Together, these findings indicate that Leptospira are ubiquitous in the slum environment and that the water-related risk to which inhabitants are exposed is low. Seasonal increases in Leptospira presence may explain the timing of leptospirosis outbreaks. Effective prevention will need to consider the spatial and temporal dynamics of pathogenic Leptospira in surface waters to reduce the burden of the disease.

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

“…Previous experiments in mice showed that if the challenge dose is not able to cause death of the animals, a portion of the sublethal dose of leptospires is able to escape the blood defenses and colonize the kidneys 31 . Furthermore, the dose of infection necessary to cause disease in natural infection remains unclear, although recent research showed that the numbers of leptospires available in the environment are low on average 32,33 . Current animal model experiments focus on unrealistic high challenge doses, which can devaluate vaccine efficacy estimation.…”

A systematic review of Leptospira in water and soil environments

“…Other turbid water sources are represented by sewage water, historically linked with human contamination among sewage-workers [5,107,108]. A recent study in a Brazilian urban slum has shown that pathogenic Leptospira DNA was detected in 36% of sewage samples and even more frequently during the rainy season, with a mean concentration of 152 bacteria per mL [7].…”

“…Water vs soil (5% vs 18%) [75] Hawaii Water vs soil (54% vs 100%) [99] Leptospira concentration (log) has a significant positive correlation with turbidity (log) Hawaii Coastal stream water [15] Higher Leptospira concentration upon rainfall Brazil Surface waters [7] High concentration and genetic diversity of Leptospira spp. in soils, supporting the hypothesis of soils being a natural habitat of Leptospira spp.…”

“…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].…”

Mechanistic dose–response modelling of animal challenge data shows that intact skin is a crucial barrier to leptospiral infection

“…The spirochaete can infect most mammalian hosts, and can be shed chronically by asymptomatic carriers [8,11]. Humans become infected after exposure to water or soil contaminated by the urine of infected animals, and Norway rats (Rattus norvegicus, hereafter referred to as rats) are the primary reservoir species in many urban settings [12,13]. A colony of infected rats can shed of the order of one billion leptospires per day [14], but leptospires do not persist at high densities in soil and water [15].…”