Climate Change and The Spread of Infectious Disease

By Benedette Cuffari, M.Sc.Aug 11 2017

The impact of the changes in the climate on infectious diseases has been a well-categorized phenomenon that has affected the daily lives of individuals throughout history. For example, during the nineteenth century, Romans would retreat to the hills during their hottest seasons to avoid malaria, whereas South Asians understood that the consumption of more heavily curried foods were less likely to cause them diarrhea during the high summer period.

While global awareness and concern of the way in which our choices affect the environment erupted during the 1970s, today’s society is more concerned than ever on the fate of our world as a result of the rapidly warming temperatures that are recorded each day. In a recent study conducted by the University of Liverpool’s Institute of Infection and Global Health, Researchers have been able to confirm the connection between climate change and infectious disease, while also providing further information on the diseases that will be most affected¹.

Global warming is attributed to the release of carbon dioxide (CO₂), greenhouse gases and other air pollutants into the environment, which would normally escape into space; these harmful gases are instead absorbed by the sunlight and solar radiation, which traps the heat that is causing the Earth to get hotter. The major consequences associated with global warming include a rise in seal levels around the world, famine, crop failure, changes in the rainfall patterns, affects to plant and animal populations, as well as a number of serious health ailments.

While the exact risk associated with the impact of climate on public health cannot be fully quantified, the interaction between the human population and the specific infectious agent is dependent upon several factors including local environmental decline, food scarcity, poverty and crowding in affected areas¹.

While it is estimated that 1.1 billion people around the world do not have access to clean water, global warming has been found to increase the already heavy burden of ensuring safe and adequate water supplies to all populations. As one of the most important basic necessities of life, water is a major component of all daily tasks such as cooking, dissolution and for basic required consumption. By further limiting the amount and quality of water to people, there will be a significant rise in deadly diseases such as cholera and typhoid, which are particularly prevalent in impoverished areas².

Climate change has also been determined to have a direct correlation with enhancing the transmission of vector-borne diseases, of which include malaria, dengue, plague and viruses that induce encephalitic syndromes to be some of the most affected by climate change. Vectors are organisms such as mosquitoes, ticks, flies and fleas, which are capable of transmitting infectious diseases between humans to animals, or vice versa³.

One of the most well known and pressing vector-borne diseases that are affected by climate change is malaria, which, in 2015, accounted for approximately 212 million documented cases and about 420,000 deaths. The infected mosquitos that carry the malaria virus can only survive in environments of high humidity and heat, therefore, the rise of the global average temperature can provide conducive environments for the further spread of malaria.

While it is apparent that several other studies have attempted to correlate both the indirect and direct factors that link climate change with the spread of certain diseases, the study conducted by the University of Liverpool Researchers depended upon the results taken from their newly developed bottom-up and quantitative risk assessment.

In their approach, the Researchers attempted to quantify the sensitivity of specific pathogens that are expected to have the largest impact on both human and domestic animal health, to the expected climate change. To determine this sensitivity marker, the Researchers compared primary and secondary climate drivers, such as moisture, rainfall, temperature, altitude, vegetation and climate change, to the number of pathogens that correlate with these factors.

Similarly, the Liverpool Researchers also compared the transmission routes for 157 pathogens, and how the frequency of the presence of certain climate drivers were closely related to the transmission route of the infectious disease⁴. For example, vector-borne and waterborne pathogens were found to have one or more climate drivers, as compared to sexually transmitted pathogens that are the least likely to be associated with a climate driver.

The study confirmed that zoonotic diseases that are capable of affecting both animals and humans, such as severe acute respiratory syndrome (SARS), HIV and Ebola were all more sensitive to climate change as compared to those that affect only human or animals.

While we are limited in our ability to halt the rapidly heating temperatures of the world that are associated with causing such devastating affects to both human and animal health, certain preventative measures can be taken to allow for the early detection of the presence of these infectious diseases.

Similarly, improving the way in which human populations are able to respond to the burden of such diseases, such as through the introduction of new water filtration systems, can have a dramatic affect on human and animal resilience to such ailments. As shown throughout history, and particularly in the results found in this study, the threat of climate change on human health remains substantial.

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References:

1. “Global Warming 101” – Natural Resources Defense Council
2. “Vector-borne diseases” – World Health Organization
3. “Global Warming and Infectious Disease” A. Khasnis, M. Nettleman. Archives of Medical Research. (2005). DOI: 10.1016/j.arcmed.2005.03.041.
4. “Systematic Assessment of the Climate Sensitivity of Important Human and Domestic Animals Pathogens in Europe” K. McIntyre, C. Setzkorn, et al. Scientific Reports. (2017). DOI: 10.1038/s41598-017-06948-9.

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