Health in a changing climate: the dynamic challenge of snake bite in South Asia

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Snakebite is a neglected tropical disease (NTD) and despite being less well publicised and studied, has a far greater impact than many other NTDs such as dengue or leishmaniasis. There are estimates of up to 120,000 deaths per year globally with considerable additional morbidity resulting, for example, from limb damage or renal failure. This burden of disease is relatively hidden as snakebite not only predominantly affects poorer countries in the tropics and subtropics, but it also mainly affects the rural poor, particularly agricultural workers and subsistence farmers in lower-middle income countries (LMICs). In many countries, snakebite is seasonal and is distributed unevenly across a country because of complex interactions between human behaviour, climate, varying geography and other factors affecting snake distributions. This means that there are substantial challenges in estimating the number of deaths and complications of snakebite. National surveys are rare because they are so difficult to carry out. The variation in numbers of snakebite across countries and over any one year means that it is difficult to estimate national and regional numbers from time-limited small local studies. This absence of accurate numbers for many countries and regions means that the problem does not get the international attention that it requires and makes it extremely difficult for local public health authorities to plan appropriate health services. Improved methodological approaches for mapping snakebite risk are therefore urgently needed, particularly when considering the potential for global environmental and climate change to exacerbate snakebite impacts. Examples such as the peak of snakebite deaths in India during the monsoon and in Bangladesh during floods illustrate the potential for environmental factors to influence disease. In Sri Lanka, bite and envenoming patterns also vary between climatic zones, with bite and envenoming incidence changing with altitude and rainfall. Climate change is thus likely to be an important yet currently unrecognised contributor to altering snakebite risk in affected areas, potentially impacting on snakebite incidence by altering snake abdundance, distributions and behaviour, altering human abundance and behaviour or both. This study aims to improve the ways in which the epidemiological burden of snakebite can be estimated and mapping risk using modelling of the interactions between snake and human distributions, behaviours and environmental factors and to investigate the extent to which climate and land-use change will impact upon this burden. The study will develop and validate methodologies using data from Sri Lanka and, in future, use these approaches to improve estimations of the snakebite burden and map risk over wider geographical areas in South Asia, and predict how they may change in the future. This approach will facilitate the diversion of appropriate resources towards addressing this major problem and will provide accurate information about the distribution of the snakebite burden at relevant scales to help health managers target resources appropriately and explore interventions that will help manage this risk and its associated socio-economic impacts in LMICs.