• P.K. Peterson

How Climate Change Fuels Infectious Diseases

“In nature nothing exists alone.” - Rachel Carson, Silent Spring

“Corona crisis is a 100-meter race and the climate crisis is a marathon. We have to run both at the same time.” - Victor Galaz, Deputy Director, Stockholm Resilience Centre SEI

April 22 is designated Earth Day, an annual event supporting environmental protections for our planet. A central concern of the approximately 1 billion people who will participate in “Restore Our Earth,” the name given to this year’s celebration, is the profound havoc that climate change continues to exact on all life on our planet. Earth Day is also, however, a celebration of the remarkable leaders in the field of ecology like Rachel Carson, the American marine biologist, conservationist, and author, who recognized that in nature “everything is connected.” This Germ Gems post describes some of the connections between climate change and infectious diseases, including the COVID-19 pandemic.

Climate change: definition and causes. At the outset, it is important to distinguish between weather—the short-term conditions of the atmosphere and climate—the weather of a specific region over a long period of time. Weather can vary or change in just a few hours whereas climate takes hundreds or even millions of years to change. The National Aeronautics and Space Administration (NASA), a leading U.S. agency that monitors environmental changes, defines climate change as a change in Earth’s climate due to a change in Earth’s usual temperature or a change in where rain and snow usually fall on Earth.

Virtually all scientists agree that humans have changed the Earth’s climate by driving cars, flying in jet planes, heating and cooling their homes, and cooking food. All these things take energy. One way to produce energy is by burning coal, oil and gas. Burning these natural resources generates “greenhouse gases,” mainly CO2 and methane. Globally, electricity generation is the single largest source of these dangerous emissions that, in turn, fuel the warming of our planet resulting in melting glaciers, rising sea levels, and violent weather extremes.

The ten top warmest years on record globally have occurred since 2005. And most climate scientists consider this relatively recent acceleration of global warming an emergency that threatens the very existence of our species.

Climate change’s link to infectious diseases: a recap. The most important infections linked to climate change are those caused by insect vectors, namely ticks and mosquitoes, whose reproductive season and geographic range are extended by warming and moisture. I have considered these infections in previous Germ Gems posts namely: Tick Talk (April 14, 2021, covering Lyme disease and Rocky Mountain spotted fever); and The Mosquito: The Most Pestilent Pest (August 10, 2019, covering malaria, dengue fever, and Zika virus infection).

Climate change has also increased water-borne infections caused by microbes that flourish in warm water. By far the most important of these infections is cholera, the subject of two of my previous posts, Cholera: When Water Turns Deadly (December 1, 2019) and Water, Water Everywhere, but Is It Safe to Drink? (March 24, 2021). And, as I discussed in Cyanobacteria (‘Blue-Green Algae’): Gotta love ‘em, gotta hate ‘em (August 24, 2019), an increase in cyanobacteria, microbes that increasingly foul the Earth’s fresh and sea water, is related to global warming.

Climate change and the COVID-19 pandemic. In the article “The Climate Crisis and Covid-19—A Major Threat to the Pandemic Response,” in the July 2020 New England Journal of Medicine, researchers at Harvard University and the University of Miami put the connections between climate change and the pandemic into perspective. They found that the intensity and frequency of climate-related extreme events—including wildfires, hurricanes, heatwaves, and droughts—disproportionately harm the health of vulnerable and economically disadvantaged people and jeopardize SARS-CoV-2 infection control.

Of the many impacts of climate change on human health, including severe weather, heat, and infectious diseases, air pollution ranks highest in terms of associated mortality. Air pollution kills an estimated seven million people globally every year. And the main culprit is a miniscule particle referred to as PM 2.5, particulate matter, or particles that are less than or equal to 2.5 microns in diameter. These particles are small enough to traverse human airways and deposit themselves in the smallest reaches of the lungs where they provoke inflammation and tissue damage. Economically marginalized people are at higher risk than others of exposure to high levels of air pollution and associated chronic illnesses.

To reinforce the danger of PM 2.5 to human health, a December 2020 Epidemiology Perspective in Science, “Wildfire smoke, a potential infectious agent,” the authors suggest that wildfire is a source for bioaerosols that can carry microbes. It has now been established that COVID-19 is primarily an airborne infection that is transmitted by bioaerosols, particles that range in diameter from 0.02 to 100 microns. SARS-CoV-2 itself is a tiny enveloped virus about 0.1 micron in diameter. Finally, an article published in Nature in January 2021, “Particulate matter (PM 2.5) as a potential SARS-CoV-2 carrier,” tied these observations together, thereby nailing an important connection between climate change and COVID-19. By fostering air pollution and the generation of PM2.5, a “pathogen” in its own right, climate change provides a vehicle for the virus SARS-CoV2 to enter the lungs.

Earth Day 2021: a better place. This past year has been one of historic devastation due to COVID-19. Nonetheless, the world is in a much better place this Earth Day than it was a year ago both with regard to the COVID-19 pandemic and climate change.

Despite its devastating effects, this pandemic has spawned international cooperation between the private sector and governments with well-funded research leading to highly effective and safe vaccines against SARS-CoV-2. According to the Associated Press, as of this writing more than half of U.S. adults have received at least one COVID-19 vaccine dose.

Moreover, two of President Biden’s first actions upon taking office were to rejoin the World Health Organization and the International Treaty on Climate Change (known as the Paris Agreement). Also, NASA is back on track, as demonstrated by naming Gavin Schmidt as its first climate advisor. An expert in climate modeling, Schmidt will help ensure that the Biden administration has critical data on greenhouse gas emission goals.

In addition, we should all expect that at his “climate summit” tomorrow, April 22, 2021, President Biden will announce a recent step to “Restore our Earth” by establishing a collaboration between the world’s two biggest emitters of greenhouse gases, the U.S. and China. To quote Secretary General of the United Nations Antonio Guterres: “No country’s immune from the climate crisis.” Therefore, anything that halts climate change will help combat current climate-related infections and is likely to improve the odds of preventing the next pandemic.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.


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