The World Health Organization (WHO) reports that “climate change poses a major, and largely unfamiliar, challenge” to public health organizations. Many tropical nations have been grappling with infectious disease for some time. However, disease spread to more temperate regions of the world is occurring with increasing frequency due to changes in regional warming patterns. This shift can lead to increases in parasitic, vector-borne, waterborne, and foodborne disease in regions that have yet to experience such outbreaks.1-3 Pathways of transmission may also evolve, allowing for previously animal-restricted diseases to be passed on to humans, as is thought to be the case with COVID-19.4 This is compounded by the increasing globalization of modern society, which can allow novel diseases to travel rapidly. A 2019 report by Doctor S. Tong, of the Shanghai Children’s Medical Centre, Shanghai Jiao Tong University School of Medicine, China and Professor Kristie Ebi of the Center for Health and the Global Environment, University of Washington, Seattle, stated that, “The health risks of a changing climate will become increasingly urgent as climate change affects the quantity and quality of food and water, increases air pollution, alters the distribution of vectors/pathogens and disease transmission dynamics, and reduces eco-physical buffering against extreme weather and climate events.”2
In addition to novel outbreaks, many existing diseases are expected to worsen and spread as a result of climate change due to shifts in the proliferation and spread of the vectors such as insects, rodents, and birds, which are known to transmit diseases to humans.1,3 In particular, the incidence of tropical diseases caused by mosquitoes is increasing since the life cycles and viral replication rates of these insects are closely tied to warmer temperatures and rainfall amounts.4 Some of the more prominent transmissable diseases are listed in the table below.
Table. More Prominent Transmissible Diseases
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| Disease | Vector/Area |
| Babesiosis | Parasite carried by Ixodidae ticks; most common in northeastern and upper midwestern United States |
| Dengue Fever | Aedes aegypti and Aedes albopictus mosquitoes, covering broad areas of Africa and Asia; easily spread by travelers to other areas of the world |
| Malaria | Transmitted by the Anopheles minimus mosquito, whichcarries a drug-resistant malaria parasite, Plasmodium falciparum; most common to Africa, south of the Sahara and parts of Oceania such as Papua New Guinea but widely prevalent in more than 100 nations |
| Yellow Fever | Aedes spp and Aedes aegypti mosquitos; transmitted primarily in tropical and subtropical areas of South America and Africa |
| Zika Virus | A aegypti mosquito; found in warm, humid areas in Central and South America, Mexico, and the southeastern United States. |
The incidence of dengue fever in Latin American countries has also increased 30-fold over the past 50 years, a shift that primarily attributed to climate change. In addition, it has been postulated that the number of ticks in North America capable of transmitting disease has increased in recent years, and their typical ranges have expanded greatly due to generally warmer temperatures in the northern United States and parts of Canada.3,6 As a result, the Centers for Disease Control and Prevention has reported an overall increase in the incidence of Lyme and other tick-borne diseases.7
Other diseases including anthrax, bird flu, encephalitis, and Hantavirus have all been reported with greater frequency in recent years due to global warming. Outbreaks of the Ebola virus in Central Africa have also been shown to follow unusual extremes of temperatures, rainfall or droughts.8
Changes in climate have contributed to public health policy, although recent outbreaks of disease have shown that more attention may be needed at government and global agency levels. Despite this, public awareness and prevention are also driven at the individual level by healthcare providers. In a 2017 review, Antonella Rossati, MD, of the department of infectious diseases, University Hospital Maggiore della Carità, Novara, Italy, wrote that because climate change has already had a major adverse impact on the health of human populations, “health professionals everywhere have a responsibility to put health at the heart of climate change negotiations.”
References
1. World Health Organization: Climate change and human health. www.who.int/globalchange/summary/en/index6.html. Accessed February 10, 2020.
2. Tong S, Ebi K. Preventing and mitigating health risks of climate change[hs1] [hs2] . Environ Res. 2019;174:9-13. doi:10.1016/j.envres.2019.04.012
3. Ogden NH, Gachon P. Climate change and infectious diseases: What can we expect? Can Commun Dis Rep. 2019;45:76-80.
4. Andersen KG, Rambaut A, Lipkin WI, etal. The proximal origin of SARS-CoV-2 [pubished online March 17, 2020]. Nat Med. doi:https://doi.org/10.1038/s41591-020-0820-9
5. Hamlet A, Jean K, Perea W, et al. The seasonal influence of climate and environment on yellow fever transmission across Africa . PLoS Negl Trop Dis. 2018:12(3);e0006284.
6. Ebi KL, Nealon J. Dengue in a changing climate. Environ Res. 2016;151:115-123. doi:10.1016/j.envres.2016.07.026
7. Centers for Disease Control and Prevention (CDC): Lyme and other tickborne diseases increasing. www.cdc.gov/media/dpk/diseases-and-conditions/lyme-disease/index.html Accessed February 10, 2020.
8. Christensen J. Climate crisis raises risk of more Ebola outbreaks. CNN.com www.cnn.com/2019/10/15/health/climate-crisis-ebola-risks/index.html. Accessed February 10, 2020.
9. Rossati A. Global warming and its health impact. Int J Occup Environ Med 2017;8(1):7-20.
