Climate change and vector borne diseases
By Lisa Bryde and Diana Yousef
Climate change continues to be a topic of interest and concern worldwide. Many people think climate change means warmer temperatures, but that is only part of the issue and a mischaracterization of the breadth of the challenge. Climate change also includes the changing of weather patterns, mainly due to the burning of fossil fuels like coal, oil, and gas. Burning fossil fuels generates greenhouse gas emissions that act like insulation around the Earth, trapping the sun’s heat and raising temperatures. As a result, the Earth is now about 1.1°C warmer than it was in the late 1800s, and droughts, water scarcity, wildfires, rising sea levels, flooding, and declining biodiversity are on the rise. Climate change could threaten our efforts to eliminate infectious diseases as we continue to realize the profound implications it has on the prevention and control of vector-borne diseases.
What are Vectors and Vector-borne Diseases?
A vector is an organism that can transmit an infectious pathogen between humans or from an animal to a human. Many of these vectors are bloodsucking insects, which ingest disease-producing microorganisms during a blood meal from an infected host (human or animal) and later transmits it into a new host, after the pathogen has replicated. Often, once a vector becomes infectious, they can transmit the pathogen for the rest of their lives during each subsequent bite/blood meal. Vectors are cold-blooded animals that thrive in warmer climates. A changing climate is likely to influence the distribution of vector-borne diseases.
The World Health Organization (WHO) identifies the major global vector-borne diseases as malaria, dengue, chikungunya, yellow fever, Zika virus disease, lymphatic filariasis, schistosomiasis, onchocerciasis, Chagas disease, leishmaniasis and Japanese encephalitis. Eight of these vector-borne diseases are considered to be neglected tropical diseases, including lymphatic filariasis and onchocerciasis. Tropical and subtropical low- and middle-income countries bear the highest burden of vector-borne diseases.
Climate change and Vector-borne Diseases
There is no doubt that a suitable climate is necessary for the emergence and persistence of a vector-borne disease. Changes in climate may affect the transmission dynamics and geographical spread of vector-borne diseases by affecting the pathogen, the vector, non-human hosts, and humans. Warmer temperatures increase the population of vectors as well as survival and feeding activity. The effects of precipitation, another component of climate change, on vector abundance is complex and context specific. Increased precipitation could provide more vector breeding sites; however, drought could also provide more breeding sites due to an increase in the use of containers for rainwater collection and storage which serves as a breeding site for certain types of vectors. Vector densities could also be influenced by ecosystem change driven by climate change, which could degrade or enhance vector habitats and species competition, or it could increase or reduce the abundance of vector predators or vector pathogens. 2
Global temperatures are likely to rise by more than 1.5° by 2100, which will accelerate rising sea levels and extreme weather events, and likely increase the incidence of vector-borne diseases, especially malaria.  Changes in temperature and humidity will likely affect the biology and ecology of the vectors and the intermediate hosts, increasing the chances of transmission of vector-borne diseases. Research conducted in Rwanda in 1994 shows one of the first pieces of evidence relating climatic warming to an increase in malaria incidence, showing that an increase in the mean minimum temperature explained 80% of the variance in the monthly malaria estimates in high altitude areas. The moving distribution of malaria vectors, as well as the variations in malaria incidence, are challenging vector control activities and impacting the achievement of malaria elimination targets in some countries.
An increase or change in the endemic range of vector-borne diseases as a result of climate change will have very serious repercussions. Endemic countries are starting to see the spread of vector-borne diseases to higher elevations or areas previously not affected, and in non-endemic areas, there is an increase in pathogens spread through travel, trade, or migration.
What needs to be done?
Climate change and the effects on vector borne diseases is a real and urgent issue affecting vector-borne disease transmission and spread, and its impacts are likely to worsen. In the face of ongoing climate change, we must intensify efforts to prevent and control vector-borne diseases.
To address the adverse impacts of climate change, there is a need for rapid reductions in greenhouse gas emissions, as well as adaptation to ongoing climate change through intensification of vector-borne disease prevention and control efforts. Attention needs to be given to new ways to control vectors, improve water and sanitation systems, and diagnose and treat vector-borne diseases. However, the responsibility does not lie solely with the public health sector. Climate action requires commitment and significant financial investments that limit global warming by reductions in greenhouse gas emissions. This will require new ways of thinking and innovations in energy, land, and transportation.
The impact of climate change on the incidence, transmission season duration, and geographic spread of vector-borne diseases presents a major threat globally, and changing weather patterns are introducing new challenges in efforts to effectively prevent, control, and eliminate vector-borne diseases. Published research points to the need for accurate forecasting and monitoring of climate change and its impact on vector-borne diseases to help accurately inform mitigation strategies.
Dr Lisa Bryde is a Senior Technical Advisor at GLIDE and has over fifteen years of experience in field epidemiology and training. She designed, developed, and delivered trainings for the Field Epidemiology Training Programs (FETPs) in the Middle East North African and Central Asia regions on behalf of the Centers for Disease Control and Prevention, USA (CDC) for nine years. She has lived and worked in the Middle East region for organizations such as the Eastern Mediterranean Public Health Network and Médecins Sans Frontières (Doctors Without Borders).
She holds a PhD in Instructional Technology and Educational Psychology, an MPH with a concentration in Epidemiology, and recently earned a PhD in Epidemiology.
Diana is a Technical Advisor at GLIDE and holds a Masters in Public Health with a focus on epidemiology from the University of Western Australia (UWA), where she previously worked as a researcher. Prior to joining GLIDE, Diana worked with the Eastern Mediterranean Public Health Network (EMPHNET), in the department of Global Health Security with a focus on rapid response teams where she had a technical role and contributed to the management and coordination of activities for all phases of projects implemented in the Eastern Mediterranean Region. Diana also worked with EMPHNET in the field of Training and Capacity Building where she also had a technical role towards building the capacity of a country’s public health workforce to detect and respond to public health threats through the establishment of Field Epidemiology Training Programs (FETPs) and other public health programs in the Middle East and North Africa region.
With her desire to continue to contribute to improving the health status of countries within the region and globally, Diana aims to advance knowledge and progress towards the elimination and eradication of Neglected Tropical Diseases (NTDs).