Climate Change and the Neglected Tropical Diseases

Abstract

Climate change is expected to impact across every domain of society, including health. The majority of the world's population is susceptible to pathological, infectious disease whose life cycles are sensitive to environmental factors across different physical phases including air, water and soil. Nearly all so-called neglected tropical diseases (NTDs) fall into this category, meaning that future geographic patterns of transmission of dozens of infections are likely to be affected by climate change over the short (seasonal), medium (annual) and long (decadal) term. This review offers an introduction into the terms and processes deployed in modelling climate change and reviews the state of the art in terms of research into how climate change may affect future transmission of NTDs. The 34 infections included in this chapter are drawn from the WHO NTD list and the WHO blueprint list of priority diseases. For the majority of infections, some evidence is available of which environmental factors contribute to the population biology of parasites, vectors and zoonotic hosts. There is a general paucity of published research on the potential effects of decadal climate change, with some exceptions, mainly in vector-borne diseases.

Keywords: Bacteria; Climate change; Helminths; NTDs; Protozoans; Vectors; Viruses; Zoonoses.

Fig. 1

The role of greenhouses in terms of climate change is to affect the balance between surface and atmospheric energy absorption and emission (the energy budget). Increasing the back radiation will affect global temperature changes, the carbon and water cycles and have both direct and indirect effects at various scales across multiple domains of organisation as illustrated in Fig. 2.

Fig. 2

Illustration of the range of scales within ecological, biogeographical, social and geographical domains of organisation that will be affected directly or indirectly by climate change. The terms ‘macro’ and ‘micro’ are relative to each domain.

Fig. 3

Known population movements attributable to climate-based issues including drought and natural disasters. Points of departure and destination are country level and based on table 2 of Obokata et al. (2014).

Fig. 4

A core concept of the IPCC (2014) report on vulnerability and adaptations is that risks to populations are formed by interactions between sources of hazard, vulnerability and exposure. In the context of NTDs, natural and anthropogenic inputs—including interventions such as WASH and vector control—combine to affect the life cycles of climate-sensitive stages (the hazard). Simultaneously a wide variety of societal inputs can affect vulnerability and exposure levels, and can lead to mitigations that modify emissions and habitats to affect the NTD-associated hazard. A lack of adaptive inputs is likely to lead to higher exposure, vulnerability, hazards and risk.

Fig. 5

Historical and potential future CO₂ emission scenarios to the year 2100, with four representative concentration pathways (RCP2.6, RCP4.5, RCP6 and RCP8.5).

Fig. 6

Generalised framework of how increases in global temperatures and regional changes to precipitation patterns may lead to increased, translocated or decreased transmission of NTDs. Central column describes particular temperature and precipitation changes associated with climate change. Left column describes intermediary steps that might be expected to increase or translocate transmission. Right column describes intermediary steps that could lead to reduced transmission.

Fig. 7

Illustration of the steps taken to map future transmission potential of S. mansoni in East Africa, combining functional trait knowledge on the relationship between temperature and Biomphalaria fecundity with dynamic agent-based models, downscaled climate projections and ecological niche modelling. The results of combining the outputs of these models and experiments resulted in a high-resolution hazard map which was then used to underpin a risk map that incorporated a vulnerability layer as observable in the Healthy Futures Atlas.