by Samantha Ricardo

Graphic design by Andrew Janeczek

The adverse effects of climate change can be readily observable. Sea level rise, shrinking glaciers, and abnormally intense wildfire seasons are only a few examples of how the changing climate is impacting our world today. Beyond its influence on weather conditions, natural habitats, and long-standing environmental monuments, climate change is also affecting human health, both directly and indirectly. One indirect health impact is the rise of infectious diseases and their transmission.  

Infections diseases are characterized by infections caused by various pathogens, including bacteria, viruses, fungi, parasites, and prions. These diseases can be transferred via a variety of modes including insect bites (vector-borne diseases), animal interaction (zoonotic diseases), and the consumption of contaminated water or food.  Pathogens require very specific conditions to survive, reproduce, and spread.¹ According to the Centers for Disease Control and Prevention (CDC), infectious diseases are on the rise. This includes diseases such as Lyme disease, West Nile disease, and Valley fever.² 

So, how exactly is climate change increasing the spread of infectious diseases? 

Migration 

Climate change is contributing to the destruction of animal habitats leading to the migration of animals and insects into regions that were previously unsuitable for these species. This is specifically relevant regarding urban environments where humans live. These migrating animals and insects often carry disease which can be transferred to humans through bites or contamination of food or water.¹ For instance, blacklegged ticks, once highly localized in the continental U.S. are migrating northwards, potentially leading to an increased occurrence of Lyme disease in Canada.³ Human climate-related migration is also a potential mechanism for infectious disease transmission. As individuals are being forced to leave their homes because of climate impacts, migration may push individuals into areas prone to infectious diseases and introduce infectious diseases to areas where diseases were previously absent. 

Enhanced survival and reproduction

Climate change in Canada has also led to longer summer seasons, milder winters, and changing rainfall patterns. Warmer temperatures can enhance the survival and reproduction of certain species of pathogens and vectors. This is particularly relevant in the context of waterborne diseases. Notably, warming oceans have provided a favorable habitat for the bacterium Vibrio cholera, which leads to cholera.¹

Increased Susceptibility

Lastly, climate change creates conditions which often leads to a scarcity of basic resources such as food, water, and suitable habitat. Individuals experiencing malnutrition or living in unsanitary environments due to these limitations are more vulnerable to contracting illnesses including infectious diseases.¹ 

While some pathogens have a lower survival rate under high temperatures and thrive in cold temperatures, the threat of disease by many other pathogens will be heighted as temperatures continue to rise and the local environments continue to change.¹ It is essential to acknowledge that the increase of infectious diseases both now and in the foreseeable future is not equally distributed across communities. Populations with fewer adaptive resources and measures in place will be more likely to experience health casualties. The spread of infectious diseases due to climate change is most pronounced in areas with inadequate sanitation, limited access to safe drinking water, and poor hygiene practices. 

So, what can be done? Traditionally, the public sphere has focused on mitigation and reversal through education, outreach, and initiatives. However, reports by the Intergovernmental Panel on Climate Change (IPCC) have confirmed that many of the climate effects caused by human activity are irreversible and unfortunately inevitable.⁴

As the effects of climate change are already being felt, health care systems have a critical responsibility to enhance support for individuals and populations at high risk for disease contraction. There are three key ways the healthcare system can play a role in adopting adaptive measures: remodeling public health infrastructure, incorporating a One Health approach within the medical system, and increasing funding for vaccine development and awareness.

Remodeling Public Health Infrastructure

Public health agencies play a crucial role in surveillance, education, and outreach. When it comes to the spread of infectious diseases, a strong emphasis should be placed on raising awareness among high-risk populations. To achieve this, education for public health agencies and professionals should have a directed focus on effective public outreach for vulnerable groups both locally and globally. 

Incorporating a One Health approach within the Medical System

The One Health approach recognizes the interconnection between human health, animal health, and environmental health.⁵ It is a multidisciplinary method to better recognize, analyze, and treat human symptoms in collaboration with different disciplines that are not localized to medicine. Regarding infectious diseases, adopting a One Health approach would involve medical professionals collaborating with health agencies responsible for monitoring infectious diseases, veterinarians, and ecologists. This collaboration would facilitate the effective dissemination of infectious disease information and a better understanding of how disease is spread among species and environments. By gaining deeper insights into the origins and transmission rates of a disease, medical professionals, clinics, and hospitals can be better equipped to treat patients and provide educational resources.  

Increasing funding for vaccine development and awareness

Vaccines are one of the most effective mechanisms for preventing infectious diseases. However, many of the infectious diseases believed to be impacted by climate change do not have vaccines associated with them or have vaccines which are in early trial stages.¹ Increased funding for vaccine research and development would be a positive step in combating an increase in infectious disease. In addition to existing infectious diseases, vaccine development should also be focused on emerging infectious diseases as climate change is likely to contribute to the expansion of new infectious diseases.⁶ For diseases in which a vaccine does exist, investment in educational and outreach programs for individuals lacking knowledge related to vaccination would be an additional positive step in preventing infectious disease occurrence.

Without proper medical preparation, intervention, and multi-disciplinary collaboration, the threat of climate change and the infectious diseases associated with it, are likely to overwhelm the health care system. Reflecting on infectious diseases which have overwhelmed the healthcare system in Canada and abroad in the past (namely COVID-19), it is crucial for the health system to respond proactively to the current challenges. By doing so, we can better serve vulnerable populations and support a functional, effective, and adaptive health system.  

References 

1. Wu, X., Lu, Y., Zhou, S., Chen, L. & Xu, B. Impact of climate change on human infectious diseases: Empirical evidence and human adaptation. Environ Int 86, 14–23 (2016).
2. Centers for Disease Control and Prevention. Climate Change and Infectious Diseases. (2022).
3. Canadian Public Health Association. Infectious Disease and Climate Change in Canada: Key informant interviews. (2021).
4. Edelson, P. J. et al. Climate Change and the Epidemiology of Infectious Diseases in the United States. Clinical Infectious Diseases 76, 950–956 (2023).
5. Mackenzie, J. S. & Jeggo, M. The One Health Approach—Why Is It So Important? Trop Med Infect Dis 4, 88 (2019).
6. Carignan, A., Valiquette, L. & Laupland, K. B. Impact of climate change on emerging infectious diseases: Implications for Canada. Official Journal of the Association of Medical Microbiology and Infectious Disease Canada 4, 55–59 (2019).