The challenge

Leptospirosis is a leading zoonotic disease (able to spread from animals to humans) in terms of morbidity (illness) and mortality (death) worldwide, with more than 1 million cases and 50,000 deaths each year. Many of these occur in the world’s most deprived areas.

High-income countries have tackled leptospirosis by reducing human contact with contaminated flood waters through improved drainage and rodent control. However, these measures are not generally implemented in low- and middle-income countries (LMICs) and currently there are no effective prevention and control measures for leptospirosis in resource-poor settings, and no safe and effective vaccines are available.

Leptospirosis has recently emerged as a major public health problem in impoverished urban settlements in tropical LMICs where transmission to humans takes place through contact with soil and water that are contaminated with Leptospira shed from the urine of the large rodent population. Poverty, poor housing, overpopulation, and lack of basic sanitation allow rat numbers to increase and create an environment in which the bacteria can survive for days to weeks. Urban transmission is characterised by annual seasonal epidemics during periods of increased rainfall and flooding events. As the global population living in urban disadvantaged and climate-vulnerable communities increases, the burden of leptospirosis is expected to increase.

What we're doing

In partnership with the University of Bahia in northeast Brazil, we are working to improve our understanding of the water-leptospirosis relationship as a way of better understanding how the disease is spread, and what controls are likely to be most effective to reduce transmission.

We will be developing a hydro-epidemiological model for the Leptospira environmental contamination process, which will be the first of its type for this organism. We will validate the model using data collected specifically for this study. We also aim to develop a quantitative microbial risk assessment (QMRA) model for Leptospira in the environment to identify where risks to public health are greatest and where interventions will be best focused. We will attempt to link this to models of future climate to create a dynamic risk assessment. Finally, we will look at the environmental engineering interventions that are best suited to the control of Leptospira presence and movement in the environment.

How it helps

By better understanding how Leptospira moves through the environment, we will be able to improve guidance on how to reduce transmission and to guide investment in interventions.

The hydro-epidemiological model will help in predicting Leptospira concentration and linking this to the QMRA model will allow us to better predict human infection risk using data. The work on environmental engineering interventions will allow us to improve recommended responses to settings with high loads of Leptospira. In the long-term this will help progress guidance more widely on Leptospira control and in the immediate term it will help inform an ongoing Wellcome Trust funded research project in Bahia, and in particular the design of shallow sewer interventions to control Leptospira.

Lead researcher

Professor Guy Howard

Investigators

University of Bristol 

• Dr Rodolfo Bezerra Nobrega

• Dr Zoe Ward

• Professor Guy Howard

University of Bahia 

• Professor Federico Costa

• Dr Max Eyre

Funders

Funding for this project has kindly been provided by the University of Bristol US Foundation.