By Gary Evans, Medical Writer
Global warming and climate change favor the continuing rise of pandemic viruses and multidrug-resistant bacteria, said Robert Bonomo, MD, distinguished professor at Case Western Reserve University in Cleveland.
“Why are we facing this? I’m going to throw out a hypothesis,” he said at the recent IDWeek 2022 Conference. “I think we are not appreciating the impact of climate change. I believe viral cross-transmission to humans is being accelerated by climate change. In bacteria, the consequence of increased temperature is increasing resistance.”
In making his case for a rise in infectious diseases as the climate warms, Bonomo cited a 2020 paper that concluded, “Human defenses against microbial diseases rely on advanced immunity that includes innate and adaptive arms and endothermy [warm-blooded], which creates a thermal restriction zone for many microbes. Given that microbes can adapt to higher temperatures, there is concern that global warming will select for microbes with higher heat tolerance that can defeat our endothermy defenses and bring new infectious disease.”1
In particular, multidrug-resistant Candida auris, a fungi that can cause invasive infections in humans, emerged rapidly in 2009 and has spread globally.
“The nearly simultaneous emergence of Candida auris on three continents, an event proposed to result from global warming, has raised the specter that increased warmth by itself will trigger adaptations on certain microbes to make them pathogenic for humans,” the authors reported.
C. auris already is established as a hospital-associated infection (HAI) and rose 60% during 2020 along with many drug-resistant bacteria that caused inpatient infections in the pandemic’s initial year, the Centers for Disease Control and Prevention reports.2
Regarding bacteria and climate change, Bonomo noted a study that argues warmer temperatures have a compounding effect on antibiotic resistance. There is a strong link between thermal stress and the evolution and maintenance of antibiotic resistance mutations, the authors noted, meaning “global changes in temperature are associated with increases in antibiotic resistance and its spread.”3
Similarly, zoonotic viruses jumping to humans via bats through an intermediate host can be expected to increase with global warming, he said. Concerningly, “at least 10,000 virus species have the ability to infect humans but, at present, the vast majority are circulating silently in wild mammals,” researchers report.4 “However, changes in climate and land use will lead to opportunities for viral sharing among previously geographically isolated species of wildlife.”
Expansion of Mosquito Range
Another IDWeek 2022 speaker warned of vector-borne diseases related to climate change, showing maps of the expanded range over time of mosquito-borne arboviruses typically seen in the Southern Hemisphere.
For example, the mosquito-borne Zika virus struck the United States in 2016 via travelers and then local transmission in Texas and Florida. The virus can cause the horrific birth defect of microcephaly if pregnant women are infected. Zika rarely has been reported in the United States, but global warming could expand the habitats of mosquitos that carry the arbovirus.
“We also notice with vector-borne diseases that, when they are exposed to populations that have never seen these diseases, we tend to see very rapid outbreaks with more severe disease,” said Sadie Ryan, PhD, associate professor of medical geography at the University of Florida.
This information should be used to plan countermeasures, warning against reverting to the typical “scare tactics” used to draw attention to climate change, she said.
“Essentially, when we talk about global warming, we are talking about radiation that comes in from space and doesn’t bounce back out,” Ryan said. “We have a huge anthropogenic component of this, and our choice is whether to slow that or help to mitigate it for the future. I am not going to tell you what to do today. I’m just going to tell you what happens whether we do or not.”
Global warming, regardless of etiology, is a scientific fact — certainly for the last 40 years. The National Oceanic and Atmospheric Administration (NOAA) reported in 2021 that “the combined land and ocean temperature has increased at an average rate of 0.14°F per decade since 1880; however, the average rate of increase since 1981 (0.32°F) has been more than twice that rate.”5
As a result, in part, to politicization of climate change and the accompanying dissemination of misinformation, the public generally has been slow to embrace global warming, and more specifically that it is largely driven by human activity. However, recent polls are finding that a clear majority believe climate change is happening, but whether and to what extent it is caused by human activity is more divided.
In contrast, science has drawn a clear conclusion. A recently published analysis of the peer-reviewed scientific papers on this question published since 2012 concluded “with high statistical confidence that the scientific consensus on human-caused contemporary climate change — expressed as a proportion of the total publications — exceeds 99% in the peer-reviewed scientific literature.”6
Co-author Benjamin Houlton, PhD, a professor of ecology and evolutionary biology at Cornell University, said in a statement: “It’s critical to acknowledge the principal role of greenhouse gas emissions so that we can rapidly mobilize new solutions.”
How Long Has This Been Going On?
Pandemics and outbreaks since the 1918 H1N1 influenza A pandemic primarily have been viral pathogens of zoonotic origin, with escape from animal reservoirs leading to human immunodeficiency virus, severe acute respiratory syndrome (SARS), Middle East respiratory syndrome, Ebola, and COVID-19, Bonomo said.
“All the cost of life that has occurred because of these viral vectors, these zoonotic pathogens finding their ways into the human host,” he said. “I ask you, was the 1918 flu pandemic a consequence of the industrial revolution? Carbon dioxide, methane, all those toxic gases started going up precipitously around the 1900s — it could be related to what we were doing to our planet. We are learning that changing Mother Earth has its consequences. The viral world is making its way across species barriers.”
Taking the logical next step, some have questioned whether SARS-CoV-2, which currently plagues the globe, is a product of climate change.
“The rise in industrialization-related human activities has created a marked imbalance in the homeostasis of environmental factors, such as temperature and other weather, and these might even have imposed conditions for the emergence of future coronavirus cycles,” researchers theorize.7 With anthropocentric stresses, such as deforestation, industrialization, and pollution, new coronavirus pandemics can be anticipated, they propose.
“Historically and until the SARS epidemic in 2003, which originated in late 2002 in China, bats were not known to carry coronaviruses,” the authors noted. “However, since that time, several species of bats have been shown to harbor multiple coronaviruses including, SARS-CoV-1.”
The only flying mammal, bats have evolved immune defenses that make them impervious to many viruses, even those deadly to human populations.
REFERENCES
- Casadevall A. Climate change brings the specter of new infectious diseases. J Clin Invest 2020;130:553-555.
- Centers for Disease Control and Prevention. COVID-19: U.S. Impact on Antimicrobial Resistance, Special Report 2022. U.S. Department of Health and Human Services, CDC; 2022. https://www.cdc.gov/drugresistance/pdf/covid19-impact-report-508.pdf
- Rodríguez-Verdugo A, Lozano-Huntelman N, Cruz-Loya M, et al. Compounding effects of climate warming and antibiotic resistance. iScience 2020;23:101024.
- Carlson CJ, Albery GF, Merow C, et al. Climate change increases cross-species viral transmission risk. Nature 2022;607:555–562.
- NOAA National Centers for Environmental Information. Monthly Global Climate Report for Annual 2021. Published January 2022. https://www.ncei.noaa.gov/access/monitoring/monthly-report/global/202113
- Lynas M, Houlton BZ, Perry S. Greater than 99% consensus on human caused climate change in the peer-reviewed scientific literature. Environ Res Lett 2021;16:114005. doi: 10.1088/1748-9326/ac2966.
- Gupta S, Rouse BT, Sarangi PP. Did climate change influence the emergence, transmission, and expression of the COVID-19 pandemic? Front Med (Lausanne) 2021;8:769208.
Professor: Global warming and climate change favor the continuing rise of pandemic viruses and multidrug-resistant bacteria.
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