Climate change is influencing the transmission and burden of many infectious diseases worldwide. Rising temperatures, shifting rainfall patterns, and more frequent extreme weather events affect how pathogens, vectors and disease hosts interact. These changes are altering the geographic ranges and seasonal activity of disease-carrying organisms such as mosquitoes and ticks, and influence the growth and survival of bacteria and other pathogens in food and water systems.IPCC, 2022: Summary for Policymakers [H.-O. Pörtner, D.C. Roberts, E.S. Poloczanska, K. Mintenbeck, M. Tignor, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem (eds.)]. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 3–33, doi:10.1017/9781009325844.001.
Infectious diseases that are sensitive to climate can be grouped into: vector-borne diseases (transmitted via mosquitos, ticks etc.), waterborne diseases (transmitted through viruses or bacteria in water), and food-borne diseases (spread through pathogens in food).Cissé, G., R. McLeman, H. Adams, P. Aldunce, K. Bowen, D. Campbell-Lendrum, S. Clayton, K.L. Ebi, J. Hess, C. Huang, Q. Liu, G. McGregor, J. Semenza, and M.C. Tirado, 2022: Chapter 7: Health, Wellbeing, and the Changing Structure of Communities. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [H.-O. Pörtner, D.C. Roberts, M. Tignor, E.S. Poloczanska, K. Mintenbeck, A. Alegría, M. Craig, S. Langsdorf, S. Löschke, V. Möller, A. Okem, B. Rama (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 1041–1170, doi:10.1017/9781009325844.009. In 2022 scientists stated a clear observation that "the occurrence of climate-related food-borne and waterborne diseases has increased."
Vector-borne diseases like dengue fever, malaria, tick-borne diseases, leishmaniasis, zika fever, chikungunya and Ebola are especially sensitive to climatic conditions. Warmer and wetter conditions expand suitable habitats for vectors, enabling them to survive in areas that were previously too cold or dry. As temperatures rise at higher elevations and latitudes, transmission risks are expected to increase in parts of North America, Europe, and highland regions of Africa and Asia. For example, the range of ticks that transmit Lyme disease and tick-borne encephalitis has expanded, and further warming could lengthen their active seasons.
Climate change also affects waterborne and food-borne diseases by influencing water quality, sanitation, and microbial ecology. Warmer waters and increased flooding promote the growth and spread of bacteria such as Vibrio cholerae, which causes cholera, and other pathogens responsible for gastroenteritis and wound infections. Drought and poor access to clean water increase the risk of contamination and exposure to diarrheal diseases, typhoid, and hepatitis A.
The health impacts of these climate-related risks are unevenly distributed. Low-income countries and communities with high socio-economic constraints and limited healthcare, infrastructure and sanitation are the most vulnerable. Nearly one in three people globally lack access to safe drinking water, which amplifies exposure to waterborne pathogens and related illnesses. These conditions can also affect mental and social well-being and place additional strain on public health systems.
Without mitigation and adaptation measures, climate-related infectious disease risks will continue to rise. Limiting greenhouse gas emissions, strengthening disease surveillance, vector control, vaccination, water and sanitation services, and climate-resilient healthcare infrastructure is seen as essential to reducing these impacts.
Background The World Health Organization considers climate change as one of the greatest threats to human health. Text was copied from this source, which is available under a Creative Commons Attribution 4.0 International License Global warming, increased rainfall, flooding and drought are some of the consequences of climate change that are leading to the escalation of vector, food and water-borne diseases. Climate change can make it easier for infectious diseases to spread to new regions and surge in areas where they were previously under control. As a result, diseases that have never previously infected humans (Disease X) may 'spill over' from animals and become a threat to humans too. More than half (218 out of 375) of infectious diseases that affect humans worldwide have already been worsened by climate change.
Mechanisms and pathways
The successful emergence or reemergence of infectious diseases depend on people coming into contact with the pathogen (for example a virus) but also on the extent to which peoples' resistance is weakened, or the pathogen is strengthened, by changes in the environment.
Climate change can increase the spread of infectious diseases through multiple possible pathways, including:
climatic hazards (such as heatwaves, wildfires, or floods) bringing the disease closer to people (e.g. shifts in the geographical range of species), climatic hazards bringing people closer to the disease (e.g. heatwaves bringing more people to recreational water activities), disease strengthened by climatic hazards (e.g. "improved climate suitability for reproduction, acceleration of the life cycle, increasing seasons/length of likely exposure", for example ocean warming can lead to increased Vibriosis outbreaks), people impaired by climatic hazards (e.g. from malnutrition due to drought conditions) climatic hazards forcing people to leave their homes (climate migration) and live in unsanitary circumstances and dense living situations such as refugee camps, increased occupational exposure to climate and climate extremes (e.g. agricultural work, construction work, disaster response work).
Infectious diseases that are sensitive to climate can be grouped into:
water-borne diseases (transmitted via viruses or bacteria, e.g.: E. Coli), vector-borne diseases (transmitted via mosquitos, ticks etc.), and food-borne diseases (e.g. Salmonella bacteria, causing Salmonellosis).
Climate change is affecting the distribution of these diseases due to the expanding geographic range and seasonality of these diseases and their vectors.
Though many infectious diseases are affected by changes in climate, vector-borne diseases, such as malaria, dengue fever and leishmaniasis, present the strongest causal relationship. One reason for that is that temperature and rainfall play a key role in the distribution, magnitude, and viral capacity of mosquitoes, who are primary vectors for many vectors borne diseases. Observation and research detect a shift of pests and pathogens in the distribution away from the equator and towards Earth's poles.
Changes to vector distribution
Climate change affects vector-borne diseases by affecting the survival, distribution and behavior of vectors such as mosquitoes, ticks and rodents. The viruses, bacteria and protozoa are carried by these vectors transferring them from one carrier to another. Vectors and pathogens can adapt to the climate fluctuations by shifting and expanding their geographic ranges, which alter the rate of new cases of disease depending on vector-host interaction, host immunity and pathogen evolution. This means that climate change affects infectious diseases by changing the length of the transmission season and their geographical range.
Climate change is leading to latitudinal and altitudinal temperature increases. Global warming projections indicate that surface air warming for a "high scenario" is 4 C, with a likely range of 2.4–6.4 C by 2100. A temperature increase of this size would alter the biology and the ecology of many mosquito vectors and the dynamics of the diseases they transmit such as malaria.
Changes in climate and global warming have significant influences on the biology and distribution of vector-borne diseases, parasites, fungi, and their associated illnesses. Regional changes resulting from changing weather conditions and patterns within temperate climates will stimulate the reproduction of certain insect species that are vectors for disease.
The vectors of transmission are the major reason for the increased ranges and infection of these diseases. If the vector has a range shift, so do the associated diseases; if the vector increases in activity due to changes in climate, then there is an effect on the transmission of disease. However it will be hard to classify exactly why the range shifts or an increase in infection rates occurs as there are many other factors to consider besides climate change, such as human migration, poverty, infrastructure quality, and land usage; but climate change is still potentially a key factor.
Mosquitoes
One major disease-spreading insect is the mosquito, which can transmit diseases like malaria, West Nile virus, and dengue fever. With regional temperatures changing due to climate change, the range of mosquitos will change as well. The range of mosquitoes and disease transmission will move farther north and south, and places will have a longer period of mosquito habitability than at present, leading to an increase in the mosquito population in these areas. This range shift has already been seen in highland Africa. Since 1970, the incidence of malaria in high-elevation areas in East Africa has increased greatly. This has been proven to be caused by the warming of regional climates.
Many major cities in Africa (e.g.: Nairobi, Harare) were sited above the mosquito breeding-transmission altitude, but due to increasing temperatures mosquitos are now more likely to thrive in these areas as well. In Europe, Dengue cases were transmitted by populations of mosquitoes established in France and Italy.
Environmental changes, climate variability, and climate change are factors that could affect biology and disease ecology of Anopheles mosquitoes and their disease transmission potential. When the temperature rises, the larvae take a shorter time to mature and, consequently, a greater capacity to produce more offspring. In turn this leads to an increase in malaria transmission to humans.
Environmental changes such as deforestation could also increase local temperatures in the highlands thus could enhance the vector capacity of the anopheles. Anopheles mosquitoes are responsible for the transmission of a number of diseases in the world, such as, malaria, lymphatic filariasis and viral fevers such as the O'nyong'nyong virus.
Environmental change and zoonotic disease emergence
Climate change is considered a significant driver of zoonotic disease emergence due to its effects on ecosystems, wildlife distribution, and patterns of human–animal interaction. Increases in global temperature, changes in precipitation, and the growing frequency of extreme weather events can disrupt ecological systems and contribute to shifts in species ranges. Such changes may increase contact between wildlife, livestock, and human populations, thereby elevating the risk of cross-species pathogen transmission.