Vector-borne diseases such as malaria, dengue, West Nile Virus, and Lyme Disease are spread by arthropods (mainly mosquitos, fleas, and ticks) that survive and thrive in environments typically found along the equator (hot, rainy, plenty of food). These infectious diseases make up a significant portion of the global burden of disease, with more than one billion people becoming infected and more than one million dying annually from illnesses like malaria, schistosomiasis, and African trypanosomiasis1. The distribution of these diseases disproportionately impacts the poor and lower class of any given society due to inadequate hygiene and water systems, less economic opportunity, and depleted access to healthcare and treatment2.
Insect vectors of disease survive and thrive in warm and wet conditions. As climate change continues to increase global temperatures and alter precipitation patterns, the range of these infectious diseases is spreading outward from the equator. Areas that once did not have to deal with diseases like malaria are now at risk for the vectors to find their way across borders. The maps below from the Stanford Institute for the Environment show the current range of the Aedes aegypti mosquito (which spreads dengue, Zika, and yellow fever), and then the range of the mosquito in 2080 if nothing is done to prevent the emission of greenhouse gases3.
Source: Sadie Ryan, Stanford Institute for the Environment
Changes in climate will bring about a change in vector-borne disease transmission and mortality. Some climate effects (such as drying) will have a protective effect while other (increased precipitation) will bring an increase in vector-borne disease morbidity. The World Meteorological Association and the World Health Organization created the diagram below to visualize the impact temperature and precipitation can have on one of these vector-borne diseases: dengue4.
Source: World Meterological Association/ World Health Organization
To properly address the looming threat of infectious disease exacerbation and spread due to climate change, research efforts need to be aligned with national priorities. Efforts do not necessarily need to be made to address the specific health risks that are directly related to climate change (which tend to be hard to parse out from other determinants of health), but instead can take a broad approach to decrease infectious disease rates in the present. This lays the basis for increasing basic public health interventions and disease-specific control measures, which are beneficial in the realm of infectious diseases but are also some of the most effective measures to protect against climate change5. Applied research programs that align with national priorities for vector-borne disease control would include:
- Assessments of the risks, including quantitative detection and attribution and scenario studies, but also more qualitative vulnerability and adaptation assessment that can explore a wider range of mechanisms6;
- Evaluation of the effectiveness of individual interventions, or control programmes, including the degree to which climate variability and change may influence their effectiveness7;
- Health impact assessment for climate adaptation and mitigation decisions that may affect vector-borne disease, such as irrigation schemes or changes in water-storage practice providing breeding sites for vectors;
- Surveillance, monitoring and associated decision-support tools, including the use of climate information as a resource to provide earlier warning of infectious disease epidemics and improve spatial targeting, for example, and connection to standard operating procedures, such as the International Health Regulations, to address public health emergencies of international concern8; and
- Assessment of financial and other resource requirements, such as the costs that would be necessary to extend vector-borne disease surveillance or control interventions to newly suitable locations or seasons.
A great example of a plan in action is the WHO Regional Office of Africa’s Adaptation to climate change in Africa: Plan of action for the health sector 2012–2016.
1. WHO. 2008. The global burden of disease: 2004 update. Geneva, Switzerland: World Health Organization.
2. Ottesen EA, Duke BO, Karam M, & Behbehani K. (1997). Strategies and tools for the control/elimination of lymphatic filariasis. World Health Organization Bulletin. 75(6):491-503.
3. Jordan, R. (2019). Stanford researchers explore the effects of climate change on disease. Stanford News. https://news.stanford.edu/2019/03/15/effect-climate-change-disease/
4. WMO/WHO. 2012. Atlas of health and climate. Geneva, Switzerland: World Meteorological Organization.
5. Campbell-Lendrum D, Manga L, Bagayoko M, Sommerfeld J. Climate change and vector-borne diseases: what are the implications for public health research and policy?. Philos Trans R Soc Lond B Biol Sci. 2015;370(1665):20130552. doi:10.1098/rstb.2013.0552
6. WHO. 2013. Protecting health from climate change: vulnerability and adaptation assessment. Geneva, Switzerland: World Health Organization
7. WHO/DFID. 2009. Vision 2030: the resilience of water supply and sanitation in the face of climate change summary and policy implications. Geneva, Switzerland: World Health Organization.
8. Thomson MC, Doblas-Reyes FJ, Mason SJ, Hagedorn R, Connor SJ, Phindela T, Morse AP, Palmer TN. Malaria early warnings based on seasonal climate forecasts from multi-model ensembles. Nature. 2006 Feb 2; 439(7076):576-9.