Linking rattiness, geography and environmental degradation to spillover Leptospira infections in marginalised urban settings: An eco-epidemiological community-based cohort study in Brazil

Abstract

Background: Zoonotic spillover from animal reservoirs is responsible for a significant global public health burden, but the processes that promote spillover events are poorly understood in complex urban settings. Endemic transmission of Leptospira, the agent of leptospirosis, in marginalised urban communities occurs through human exposure to an environment contaminated by bacteria shed in the urine of the rat reservoir. However, it is unclear to what extent transmission is driven by variation in the distribution of rats or by the dispersal of bacteria in rainwater runoff and overflow from open sewer systems.Methods: We conducted an eco-epidemiological study in a high-risk community in Salvador, Brazil, by prospectively following a cohort of 1,401 residents to ascertain serological evidence for leptospiral infections. A concurrent rat ecology study was used to collect information on the fine-scale spatial distribution of ‘rattiness’, our proxy for rat abundance and exposure of interest. We developed and applied a novel geostatistical framework for joint spatial modelling of multiple indices of disease reservoir abundance and human infection risk.Results: The estimated infection rate was 51.4 (95%CI 40.4, 64.2) infections per 1,000 follow-up events. Infection risk increased with age until 30 years of age and was 37 associated with male gender. Rattiness was positively associated with infection risk for residents across the entire study area, but this effect was stronger in higher elevation areas (OR 3.27 95%CI 1.68, 19.07) than in lower elevation areas (OR 1.14 95%CI 1.05, 1.53).Conclusions: These findings suggest that, while frequent flooding events may disperse bacteria in regions of low elevation, environmental risk in higher elevation areas is more localised and directly driven by the distribution of local rat populations. The modelling framework developed may have broad applications in delineating complex animal-environment-human interactions during zoonotic spillover and identifying opportunities for public health intervention.Funding: This work was supported by the Oswaldo Cruz Foundation and Secretariat of Health Surveillance, Brazilian Ministry of Health, the National Institutes of Health of the United States (grant numbers F31 AI114245, R01 AI052473, U01 AI088752, R01 TW009504 and R25 TW009338); the Wellcome Trust (102330/Z/13/Z), and by the Fundação de Amparo à Pesquisa do Estado da Bahia (FAPESB/JCB0020/2016). MTE was supported by a Medical Research UK doctorate studentship. FBS participated in this study under a FAPESB doctorate scholarship.

Topography and environmental deficiencies are associated with chikungunya virus exposure in urban informal settlements in Brazil

“…This pattern could also be seen in the maps of household locations with seropositivity marked in Figure 1. In this urban informal setting, living closer to the bottom of the valley is indicative of greater social marginalisation, with households located in these areas found to have lower socioeconomic status [30], poorer WASH infrastructure provision, low-quality housing, inadequate trash disposal and a greater risk of exposure to contaminated floodwater [31]. One explanation for why this may be protective for CHIKV exposure, may be that these low elevation areas are also the least urbanised, consisting of vegetation and soil land cover rather than concrete paving and with a lower population density than higher elevation areas, and are at high-risk of severe and regular flooding with highly contaminated water (due to open sewers and other sources of environmental contamination).…”

Gender differences in the perception of leptospirosis severity, behaviours, andLeptospiraexposure risk in urban Brazil: a cross-sectional study

“…Data was collected during mornings from Monday – Sunday in attempt to include both employed and unemployed participants and mitigate selection bias. Trained phlebotomists visited participant homes, collected blood samples, and conducted a modified version of a standardised that has been validated previously (4,19). Houses were revisited up to five times in participants were not present at the time of the previous visit.…”

“…Data were cleaned and analysed in R version 4.3.1 (41). Various R packages were used including ‘lme4’, ‘splines’, and ‘qgam’ (19,42–46).…”

“…Leptospirosis is more prevalent in men, who suffer from a higher estimated global health burden and are reported as being at greater risk of Leptospira infection across a wide range of geographical contexts (13). This is the case in climate-vulnerable urban informal settlements in Brazil where men are reported to have over twice the risk of Leptospira infection than women (4,8,18,19). While the mechanisms driving this gender difference in infection rates are poorly understood (4,14,17,18), they have largely been attributed to exposures that are more prevalent in men, and there is no evidence to suggest that they are caused by physiological differences between sexes (8).…”

“…The persistence of leptospires makes the environment an important reservoir and source of infection for humans through contact with soil, mud, and water. Flooding exacerbates this problem by dispersing leptospires across the environment and bringing humans directly into contact with contaminated flood water, increasing the risk of spillover transmission at the human-animal-environment interface (4,8,15–17).…”