Climate Change & Increased Infectious Diseases

In March 2022, the Intergovernmental Panel on Climate Change (IPCC) issued a report which warned that without swift climate action there would be a global escalation of infectious diseases.  Climatic conditions are becoming increasingly suitable for the transmission of multiple human pathogenic diseases through both direct and indirect ways. Changing climate directly affects the biological features of pathogens by amplifying growth rates, antibiotic resistance, and creating conditions more hospitable for the survival of the pathogens in both new geographical regions and over longer periods of time. Climate change indirectly increases the suitable transmission of multiple human pathogenic diseases through rapid modifications of ecosystems and changes in human behaviour, such as humans moving into closer contact with animals and insects. The societal disruptions of widespread infectious disease, as revealed by COVID-19, remind us we live in an interconnected, interdependent, and environmentally constrained world.

Let’s look at some of the ways climate change contributes to increased infectious diseases in more detail.

Rising Temperatures

Global surface temperature increased at an unprecedented rate over the last 50 years and will continue to do so. New research finds that over half of all pathogenic diseases have been exacerbated by rising temperatures. Milder winters, warmer summers, and fewer days of frost make it easier for infectious diseases like Lyme Disease, West Nile Virus, and Malaria to reproduce and expand.

Malaria is a serious and sometimes fatal mosquito-borne disease. A study in the Sistan and Baluchistan provinces in Iran found that temperature and humidity over 60% resulted in a significant positive impact on the incidence of Malaria. An increase of 1-degree Celsius minimum temperature in a specific month caused a significant increase of nearly 25% in Malaria incidence in the next month respectively.

Lyme Disease vector surveillance in Canada has documented a geographic range expansion of the black-legged tick, the main vector of Lyme Disease. The example is associated with elevated temperatures, with the number of cases of Lyme disease projected to expand by 20% in a 2 degrees Celsius warming scenario.

Additionally, more favourable temperatures and increased rainfall by 2050 from climate change could increase the suitability for Dengue (the principal mosquito vector of many diseases such as Dengue, Chikungunya, Yellow Fever, and Zika Virus), in Southern and Western Africa, South-Eastern USA, Central Mexico, Northern Argentina, and inland areas of Australia. Potential transmission season is anticipated to lengthen by 4 months due to increased climate suitability.

Rising temperatures can also increase water and food-related diseases. For example, increased surface water temperature can lead to prolonged seasonal abundance of cholera bacteria, and higher environmental temperature can assist the survival and multiplication of salmonellosis increasing the risk of food-borne diseases.

Furthermore, global warming is causing polar ice caps and permafrost to melt, exposing humans to pathogens that have been ling frozen underground. In 2016, a 12-year-old boy died in Russia after becoming infected with Anthrax. The disease was traced back to an infected reindeer carcass that had been frozen underground but emerged and thawed due to temperatures in the Siberian tundra reaching up to 35 degrees Celsius that summer.

Most alarmingly, higher temperatures allow bacteria to divide and reproduce more quickly—as demonstrated with COVID-19—creating a higher risk of the bacteria developing antibiotic resistance. Antimicrobial resistance (AMR) occurs when bacteria, viruses, fungi, and parasites change over time and no longer respond to medicines making infections harder to treat and control.

Geographical Movement

Because of climate change, some parts of the world are becoming inhospitable to humans, forcing large populations to expand into new geographical areas. Additionally, through destructive practices linked to the global fossil fuel industry (such as deforestation), disease-carrying animals like rodents and bats are moving closer to human populations. The result is an increasingly larger amount of people are living in closer contact with wild animals which provides more opportunities for diseases to pass between animals and people. Contact issues are exacerbated by international travel and trade. As seen in with the COVID-19 pandemic, infectious diseases can spread rapidly across national boundaries.

Other Factors to Consider

            Increased droughts, declining pollinators, and extreme storms make it harder to grow food, and some crops are also becoming less nutritious because of atmospheric changes, making people more susceptible to malnutrition and disease. Air pollution, whether from industrial emissions or smoke from fires clearing forests, can lead to cardio-respiratory illnesses, limiting a person’s ability to recover from infectious diseases. Furthermore, the increasing intensity, frequency and duration of climate-related disasters may jeopardize disease control efforts—for example: navigating social distancing measures during a climate emergency becomes very challenging. An extreme weather event, such as a hurricane, can result in flooding or disrupted vector control programs because of infrastructure vulnerabilities. Contamination of floodwater with pathogens or high mosquito populations, caused by stagnant floodwater can cause population exposure to pathogens, triggering events such as water-borne or mosquito-borne outbreaks.

Reframing Global Health

Several interdisciplinary and intersectional concepts have been proposed to offer a proactive and holistic framework for tackling global health threats, such as: Eco Health, One Health, and Planetary health. These concepts share the notion that the health of humans, plants, animals, and the planet is inextricably linked. The One Health approach involves experts in human, animal, environmental health, and other relevant disciplines in monitoring and controlling public health threats and to learn more about how diseases spread among people, animals, plants, and the environment. Going forward, communication and coordination between all areas of expertise is essential.

The looming global health crisis requires significant cooperation across borders, with governments, NGOs, health agencies, scientists, ecologists, and international organizations working together in open, collaborative, and constructive ways. The COVID-19 pandemic revealed a lack of cooperation in global health in areas like vaccine distribution. Despite the creation of the COVAX initiative (a global vaccine distribution scheme), high-income countries turned their backs on the Global South, hoarding supplies to triple and quadruple dose their own populations instead of allowing at-risk nations to access their first rounds of vaccination. The failure of governments in the Global North to provide access to critical treatment for the Global South is extremely problematic in terms of global health equity because populations in the South already face disproportionate health risks from a variety of factors including inadequate health facilities, poor water, sanitation, and hygiene infrastructure; high rates of wage labor migration; and close living quarters. Substantial changes are required in the structures, policies, and practices of global health governance—towards measures that are long-term solution oriented and grounded in a framework of health justice and equity. In building this framework, we must take into consideration the oppressive forces and structural disadvantages that affect global health.

References

BMJ, Strengthening the Global Response to Climate Change and Infectious Disease Threats, 2020: https://www.bmj.com/content/371/bmj.m3081

CDC, Malaria 2021: https://www.cdc.gov/parasites/malaria/index.html

CDC, One Health Basics, 2022: https://www.cdc.gov/onehealth/basics/index.html

CDC, Our Risk for Infectious Diseases is Increasing Because of Climate Change, 2022: https://www.cdc.gov/ncezid/what-we-do/climate-change-and-infectious-diseases/index.html

IPCC March 2022 Report, https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_FullReport.pdf

Paz, Shlomit, Azeem Majeed, and George K Christophides. 2021. “Climate Change Impacts on Infectious Diseases in the Eastern Mediterranean and the Middle East (EMME)—risks and Recommendations.” Climatic Change 169 (3-4): 40–40. https://doi.org/10.1007/s10584-021-03300-z.

Semenza, Jan C., Joacim Rocklöv, and Kristie L. Ebi. 2022. “Climate Change and Cascading Risks from Infectious Disease.” Infectious Diseases and Therapy 11 (4): 1371–90. https://doi.org/10.1007/s40121-022-00647-3.

The Lancet Microbe, Climate Change: Fires, Floods and Infectious Diseases, 2021: https://www.thelancet.com/journals/lanmic/article/PIIS2666-5247(21)00220-2/fulltext

World Economic Forum, Climate Change is Making Infectious Diseases Worse, 2022: https://www.weforum.org/agenda/2022/08/climate-change-making-infectious-diseases-worse/ World Health Organization, AMR, 2022: https://www.who.int/health-topics/antimicrobial-resistance

Hope Elizabeth Tracey
No Thoughts on Climate Change & Increased Infectious Diseases

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