Climate Change on Vector Borne Diseases

Updated: Jan 23


Global warming proves to be a persistent problem in our current world. The August U.N. climate change report stated that, optimistically, the climate will not stabilize until at least 20-30 years in the future. [1] When assessing the health hazards of climate change, direct effects of the temperature change such as heat stroke often come to mind. However, climate change will greatly affect disease spread in many ways, including reduction of access to clean water, overcrowding, and malnourishment. Out of the numerous factors, vector-borne diseases, diseases that are transmitted via other creatures, are one of the most consequential ways that the warming climate will change disease spread. The data shows that vector transmitted diseases will shift from tropical areas to more temperate areas, [2] with a variety of human-related factors that may both increase or decrease the spread of disease worldwide, such as immunity and healthcare access.


Temperature highly affects the ability for vectors to spread disease, due to how most disease vectors are cold blooded and how their survival is influenced by their environment. [3] Thus, the diseases they transmit are often limited to the latitudes that the vectors can develop in. [4] Mosquitoes, one of the most prominent disease vectors for humans, are confined to the tropical latitudes due to the thermal traits they possess. However, that optimal range of temperature is shifting into the temperate regions, between the Tropic of Cancer and the Arctic Circle and the Tropic of Capricorn and the Antarctic Circle, bringing diseases like malaria with it. [5] In addition to the shift in location, global warming is also increasing vector survivability by increasing the variability of climate and decreasing the variability of temperature. [6]


Due to the small range of temperatures that vectors tend to survive in, there will be the extinction of many disease vectors. However, this is likely not going to reduce disease spread enough to offset the increase in vector metabolism, since the most effective disease spreaders are also the vectors that tend to adapt and survive better under changes in the environment.


There are many confounding factors about people that makes it difficult to predict the extent of the harmfulness of disease migration. Factors such as population density, population immunization, and malnourishment indicate a higher level of disease. Temperate climates tend to have higher population densities, due to the larger number of cities, allowing disease vectors to infect an increased number of contacts, spreading disease much faster. Additionally, people who live in the original areas where the vectors live tend to have developed a higher level of herd immunity than the temperate areas, leading to a higher amount of disease spread when the vectors move to an area with little to no immunity. Due to changes in climate, foods that used to grow abundantly in temperate climates will no longer be able to survive, causing malnourishment, which hinders the ability to fight off disease. Although there are many factors that indicate that there will be more disease spread, there are a few key factors that indicate less.


The critical factor of healthcare quality and access makes it difficult to even conclude that disease spread would even increase, despite the multitude of factors that signal otherwise. Generally, temperate regions have better health infrastructures, allowing access to healthcare before the disease spreads too much.[3] Vector-borne diseases disproportionately hit lower-income individuals, due to lack of ability to do as comprehensive vector control. [7] However, despite these factors, there is a general consensus among epidemiologists that vector transmitted disease will increase as the climate warms. [3]


Regardless, global warming is drastically going to change how vector related disease spreads. The best case scenario of disease vectors staying contained to where they are normally is already an impossibility. While there are factors that can limit the spread of vector-borne diseases, they only will be able to do so with preparedness. Unless future disease control policies account for vector migration, unprepared hospitals will be expected to deal with outbreaks of diseases that were rare in the area, making severe outbreaks a near certainty. Additionally, policy makers should account for disease spread as an indirect risk of climate change, and factor it into their calculations about the extent to which they need to limit climate change.


References:

  1. Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou. (2021). IPCC, 2021: Climate Change 2021: The Physical Science Basis. Cambridge University Press

  2. Rocklöv, J., & Dubrow, R. (2020). Climate change: an enduring challenge for vector-borne disease prevention and control. Nat Immunol, 21, 479–483. https://doi.org/10.1038/s41590-020-0648-y

  3. Khasnis, A. A., & Nettleman, M. D. (2005). Global Warming and Infectious Disease. Archives of Medical Research, 36(6), 689-696. https://doi.org/10.1016/j.arcmed.2005.03.041

  4. Harvell, C. D., Mitchell, C. E., Ward J. R., Altizer, S., Dobson, A. P., Ostfeld, R. S., & Samuel, M. D. (2002). Climate Warming and Disease Risks for Terrestrial and Marine Biota. Science, 296(5576), 2158-2162. https://doi.org/10.1126/science.1063699

  5. Mordecai, E.A., Caldwell, J.M., Grossman, M.K., Lippi, C.A., Johnson, L.R., Neira, M., Rohr, J.R., Ryan, S.J., Savage, V., Shocket, M.S., Sippy, R., Stewart Ibarra, A.M., Thomas, M.B. & Villena, O. (2019). Thermal biology of mosquito-borne disease. Ecology Letters, 22, 1690-1708. https://doi.org/10.1111/ele.13335

  6. Rohr, J.R., & Cohen, J.M. (2020). Understanding how temperature shifts could impact infectious disease. PLOS Biology, 18(11), e3000938. https://doi.org/10.1371/journal.pbio.3000938

  7. Wilson, A. L., Courtenay, O., Kelly-Hope, L. A., Scott, T. W., Takken, W., Torr, S. J., & Lindsay, S. W. (2020). The importance of vector control for the control and elimination of vector-borne diseases. PLoS neglected tropical diseases, 14(1), e0007831. https://doi.org/10.1371/journal.pntd.0007831


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